GB1596074A

GB1596074A - Acoustic translation of quadraphonic signals for two- and four-speaker sound reproduction

Info

Publication number: GB1596074A
Application number: GB1651678A
Authority: GB
Original assignee: Victor Company of Japan Ltd; Nippon Victor KK
Current assignee: Victor Company of Japan Ltd; Nippon Victor KK
Priority date: 1977-04-28
Filing date: 1978-04-26
Publication date: 1981-08-19
Also published as: DE2818951C2; DE2818951A1

Description

(54) ACOUSTIC TRANSLATION OF QUADRAPHONIC SIGNALS FOR TWO- AND FOUR-SPEAKER SOUND REPRODUCTION (71) We, NIPPON VICTOR KABUSHIKI KAISHA, a corporation organized under the laws of Japan, of No 3-12, Moriyacho, Kanagawa-ku, Yokohama City, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates generally to stereophonic sound recording and reproduction systems, and more particularly to acoustic translators which permit localization of sonic images so as to provide a set of four-channel signals which is compatible to both two-channel and fourchannel reproduction systems.

In conventional quadraphonic sound recording, the microphones are so arranged with respect to each other and the recorded signals are so synthesized as to create a desired acousto-psychological effect in a specific arrangement of four speakers. It is often desired to reproduce the quadraphonic recorded material on twospeaker systems, which is usually effected by combining the components of the quadraphonic signals to produce a pair of output signals to be delivered to the speakers. However, the two-speaker reproduction of the quadraphonic signals results in localization of sonic images at different positions from those as originally intended in the four-speaker reproduction.

According to the present invention, in one aspect, there is provided an apparatus for modifying four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising: first binaural localization network means receptive of signals from a first signal source for developing a first binaural representation of said first signal, said first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of signals from a second signal source for developing a second binaural representation of said second signal, said second binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a second location;; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will - produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to provide a first additive output signal; second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to provide a second additive output signal;; first algebraically combining means to provide summation of said first additive output signal and signals from a third signal source; and second algebraically combining means to provide summation of said second additive output signal and signals from a fourth signal source.

In another aspect the present invention provides an apparatus for modifying fourchannel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising: first binaural localization network means receptive of signals from a first signal source for developing a first binaural representation of said first signal, said first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of signals from a second signal source for developing a second binaural representation of said second signal, said second binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a second location;; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means and signals from a third signal source to develop a first additive output signal; and second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means and signals from a fourth signal source to develop a second additive output signal.

The invention, in another aspect, provides a method for processing fourchannel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising the steps of: modifying signals from a first signal source to develop a first pair of first and second binaurally correlated signals which render said first signal to appear to originate from a first location; modifying signals from a second signal source to develop a second pair of first and second binaurally correlated signals which render said second signal to appear to originate from a second location;; modifying said first pair of first and second binaurally correlated signals to develop a first pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said first pair of first and second binaurally correlated signals were directly used to produce sounds; modifying said second pair of first and second binaurally correlated signals to develop a second pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said second pair of first and second binaurally correlated signals were directly used to produce sounds; providing summation of said third signals of said first and second pairs to produce a first additive output signal; ; providing summation of said fourth signals of said first and second pairs to produce a second additive output signal; providing summation of said first additive output signal and signals from a third signal source to produce a first localized output signal; and providing summation of said second additive output signal and signals from a fourth signal source to produce a second localized output signal.

In a further aspect the invention provides a method for processing four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising the steps of: modifying signals from a first signal source to develop a first pair of first and second binaurally correlated signals which render said first source signal to appear to originate from a first location:: modifying signals from a second signal source to develop a second pair of first and second binaurally correlated signals which render said second source signal to appear to originate from a second location; modifying said first pair of first and second binaurally correlated signals to develop a first pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said first pair of first and second binaurally correlated signals were directly used to produce sounds;; modifying said second pair of first and second binaurally correlated signals to develop a second pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said second pair of first and second binaurally correlated signals were directly used to produce sounds; providing summation of said third binaurally correlated signals and signals from a third signal source to develop a first additive output signal; and providing summation of said fourth binaurally correlated signals and signals from a fourth signal source to develop a second additive output signal.

These aspects of the invention permit quadraphonic signals to be made to appear to origin ate from desired positions so as to simulate a pseudo-quadraphonic effect in two-speaker arrangements.

The invention is also applicable to the modification and reproduction of fourchannel stereophonic signals using four loudspeakers. According to this aspect of the invention there is provided apparatus for reproducing four-channel stereophonic signals including a first summation signal (Rf+Rb), a second summation signal (Lf+Lb), a first difference signal (Rf-Rb) and a second difference signal (Lf-Lb) using a set of four loudspeakers arranged in spaced relation to each other, comprising:: means for converting said first and second summation signals and said first and second difference signals to develop a set of signals Rf, Lf, Rb and Lb; first binaural localization network means receptive of said signal Rf (or Rb) for developing a first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of said signal Lf (or Lb) for developing a second binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a second location;; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to provide a first additive output signal for energization of a first loudspeaker; second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to provide a second additive output signal for energization of a second loudspeaker;; means for applying said signals Rb (or Rf) and Lb (or Lf) to third and fourth loudspeakers, respectively.

In all aspects the present invention involves the use of a plurality of cascaded or tandem connections of a binaural localization network and a crosstalk cancellation network and a plurality of additive networks which are associated with the crosstalk cancellation networks. Each of the binaural localization networks is in receipt of a respective one of the original quadraphonic signals to generate a set of first and second binaurally correlated signals which are coupled to the associated crosstalk cancellation network to produce a set of third and fourth signals. The localization network is so basically designed that the first and second signals may create the impression of sound coming from a desired angle to the centre line of a listener's position, on the assumption that these signals were directly sensed by the listener's respective ears.The crosstalk cancellation network modifies the first and second signals so as to eliminate crosstalk which might be perceived by the listener when seated at distances from the speakers if the first and second signals were used to directly energize the speakers. In the case of two speaker reproduction the binaurally correlated, crosstalk-free signals are then combined in adders to give a pair of output signals to be delivered to the two speakers in front of the listener. In the case of four speaker reproduction, the converted signals Rb and Lb can be applied to third and fourth speakers directly or via third and fourth binaural localization network means and crosstalk cancellation means.By suitably selecting the frequency and delay parameters of the localization networks, the output signals from the adders, which would normally in two speaker arrangements be made to appear to originate from the two loudspeaker positions or from positions between them, may be made to appear to originate from anywhere in a 180 degree plane.

The invention will be more clearly understood from the following description which is given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is an illustration of the basic functional blocks of all aspects of the apparatus of the invention including a cascaded connection of a binaural localization network and a crosstalk cancellation network shown connected to a pair of loudspeakers; Fig. 2 is a pictorial diagram illustrating the relation to one another of sound pressure waves radiated from two loudspeakers in producing an arbitrarily located sonic image in accordance with the localization network of Fig. 1; Figs. 3-5 are suitable frequency characteristics of the binaural localization network;; Fig. 6 is a schematic block diagram of a first embodiment of the invention which permits reproduction of a pseudoquadraphonic effect in a two-speaker arrangement; Fig. 7 is a schematic diagram of a preferred modification of the embodiment of Fig. 6; Figs. 8-9 are schematic diagrams of modifications of the embodiment of Fig. 6; Fig. 10 is a schematic diagram of a second embodiment of the present invention which permits reproduction of a quadraphonic effect in a four-speaker arrangement based upon the localized output signals of the embodiment of Fig. 6; Figs. 11--12 are schematic diagrams of modifications of the embodiment of Fig. 10;; Fig. 13 is a schematic diagram of a third embodiment of the invention which permits reproduction of a pseudo-quadraphonic effect in a two-speaker arrangement based upon the non-localized quadraphonic signals; Figs. 1416 are schematic diagrams of modifications of the embodiment of Fig. 13; Fig. 17 is a schematic diagram of a fourth embodiment of the invention which permits reproduction of a quadraphonic effect in a four-speaker arrangement based upon the localized output signals of the embodiment of Fig. 13; Fig. 18 is a schematic diagram of a modification of the embodiment of Fig. 17; and Fig. 19 is a pictorial diagram of an arrangement of four speakers utilized in the embodiment of Fig. 17.

Fig. 1 illustrates the basic functional blocks of the invention. An input audio signal, which carries no information as to the localization of the source of the audio signal, such as monaural signal or a respective channel signal of stereophony, is applied to an input terminal 10 of a binaural localization network 12. The localization network 12 is to localize the origin of acoustic energy at any desired location with respect to a listener as depicted in Fig. 2.

Assume that in Fig. 2 the listener 15 has an impression that he hears sound coming from a virtual sound source 16 which is located at a position at an angle o from the center line of his position. If a signal with an intensity level S is radiated from the sound source 16, the signal will be transmitted over acoustic paths having transfer function represented by Sf and Sn to the listener 15 to produce sound pressures Le' and Re' at the respective ears of the listener. The sound wave pressures are expressed by the following matrix representation:

Equation 1 can be rewritten as follows:

The binuaral localization network 12 includes a filter circuit 20 having a particular frequency response characteristic as illustrated in Fig. 3 to simulate the transfer function Sn, and a filter-and-delay circuit 21 having amplitude-difference and delay characteristics as a function of frequency as illustrated in Figs. 4 and 5 to simulate the transfer function Sf/Sn. As shown in Fig. 3, the network 20 has resonant peaks at frequencies in the audible frequency spectrum. The resonant peaks occur at particular frequencies associated with the displacement angle 0 from the center line of the listener 15.For example, a resonant peak occurs at approximately 4 kHz for a displacement angle of zero degree while it occurs at approximately 5 kHz for a 90-degree displacement with an attendant small resonant peak or hump at 0.5 kHz.

For a 180-degree displacement, a primary resonant peak occurs at approximately 4 kllz and a small resonant peak at approximately 10 kHz with an anti-resonant peak at approximately 9 kHz. The frequency response characteristics Sn with a displacement angle 0 as a parameter is determined by plotting as a function of frequency the output from a microphone mounted in the position of the right ear of an artificial or dummy head oriented with respect to a sound source at a desired angle of displacement.

Fig. 4 depicts the amplitude-differential component of the transfer function Sf/Sn which is determined by a measurement of the difference between sound pressures Re' and Le' and plotting it as a function of frequency for a given displacement angle 0.

The sound pressure Re' is available from the output of the microphone mounted in the right ear of the dummy head referred to above, while the sound pressure Le' is obtained from the output of another microphone mounted in the corresponding position of the left ear of the dummy head.

As illustrated in Fig. 4, the amplitude difference increases with frequency in a range from approximately 0.2 kHz to 10 kHz and varies appreciably between different displacement angles. Fig. 5 shows the delay component of the transfer function Sf/Sn which is obtained from a plot of the difference in transmission time between signals corresponding to sound pressures Re' and Le' as a function of frequency for a given displacement angle 0.

As illustrated, the delay component decreases with frequency with different tendencies between displacement angles.

It is to be understood from the above discussion that the binaural localization network 12 develops a binaural or headreferenced representation of an input monaural signal so that its output is binaurally correlated signals which localize a binaural or head-referenced sonic image at a desired location with respect to a listener.

Referring again to Fig. 1, the filter-anddelay circuit 21 is connected to receive the output from the filter circuit 20 to deliver an output signal Ls. The output signal from the filter circuit 20 is a signal Rs which together with the signal Ls would produce the same sound pressures Re' and Le' if the loudspeakers that are fed with these signals individually are located very close to the respective ears of a listener. However, under normal sound reproduction, the listener is seated at distances from the speakers so that he would hear unwanted sound in addition to wanted sound, a phenomenon known as acoustical crosstalk, if the signals Ls and Rs are directly fed to the speakers.

The crosstalk cancellation circuit 14 is to eliminate such crosstalk phenomenon by modifying the input signals Ls and Rs into crosstalk-free signals Lsp and Rsp which, when fed to left and right speakers L and R, respectively, would produce a cancelling effect on the crosstalk components of the sound waves arriving at the listener's ears.

This is done by equating the resultant sound pressures Le and Re at the left and right ears of a listener 18 seated at equal distances from the speakers L and R to the sound pressures Le' and Re' described in connection with Fig. 2. Therefore, the following relation should hold:

where A is the transfer characteristic of the paths between speakers L and R and the listener's left and right ears, respectively, and B is the transfer characteristic of the crossover paths between the speakers L and R and the listener's right and left ears, respectively.

The signals Lsp and Rsp are thus given as follows:

where, T is a delay time which must be included for practical purposes and K-l is an inverse matrix of K. By rearranging Equation 4 the following relations are obtained: 1/A B Lsp=-(Ls- Rs) T 1-(B/A)2 A 1/A B Rsp=-(Rs- -Ls) T 1-(B/A)2 A To implement Equations 4a and 4b, the crosstalk cancellation network 14 is comprised by a subtractor 23 connected to receive the signal Rs and a subtractive signal (B/A) Ls through a filter-and-delay network 27 having a transfer function represented by B/A.The algebraically combined output signal from the subtractor 23 is fed to a filter-and-delay network 28 having a transfer function represented by T/A l-(B/A)2 Since the output signal from the subtractor 23 is Rs-(B/A)Ls, the resultant signal Rsp at the output of the network 28 is identical to that obtained by Equation 4b. In a similar manner, a subtractor 25 is provided to receive the signal Ls and a subtractive signal (B/A)Rs through a filter-and-delay network 26 having a transfer function represented by B/A to deliver an algebraically combined output signal Ls-(B/A)Rs to a filter-anddelay network 29 having an identical transfer function to that of network 28, all of which networks are arranged symmetrically with respect to the networks which produce signal Rsp so as to derive signal Lsp.

Referring to Fig. 6 a first embodiment of the invention is illustrated incorporating the basic functional blocks as described previously. A set of right-forward (RF), leftforward (LF), right-backward (RB) and leftbackward (lib) signals are applied respectively to the inputs to binaural localization networks 12-1, 12-2, 12-3 and 12-4 and thence to crosstalk cancellation networks 141, 142, 143 and 144, respectively.The right and left signals of each forward and backward pair are stereophonic correlated signals which may be derived from respective microphones or a program source such as a four-channel sound tape, and each of these signals is itself a monaural signal. After processing through each cascaded connection of the localization and crosstalk cancellation networks, each monaural signal is converted into a pair of binaurally correlated right and left signals.A set of adders 31, 32, 33 and 34 is provided: the adder 31 providing summation of the right components RFr and Lb of the outputs of the cancellation networks 141 and 1P-2 to deliver a summation output signal RFa and the adder 32 providing summation of the left components RFL and LFl of the outputs of the cancellation networks 141 and 142 to deliver a summation output signal LF < =. Similarly, adders 33 and 34 deliver summation output signals RBA and LB, which are respectively the summation of Rnr and LBr and the summation of RBI and Lob1, respectively. The summation outputs Ref" and RB, are algebraically combined in an adder 41, which results in a right-channel output signal Ra for delivery through amplifier 51 to the right speaker R, while the summation outputs La and LB(l are algebraically combined in an adder 42 to generate a left-channel output signal La for delivery through amplifier 52 to the left speaker L.

It will be understood that since each of the localization networks is designed to provide localization of a sonic image at any desired location upon reproduction, it is possible to localize virtual or phantom sources anywhere within a range of 180degree plane in front of a listener 53.

Since it is desirable to permit a fourchannel record to be reproduced on fourspeaker systems as well as on two-speaker systems, the use of a matrix circuit 40 shown in Fig. 7 is preferred, which circuit provide summation outputs Ra and La and difference signals Rd and Ld for rear speakers (not shown) in the case of fourchannel reproduction. The matrix 40 includes, in addition to adders 41 and 42, subtractors 43 and 44, the subtractor 43 providing subtraction of output signal R from output signal RFa to provide difference signal Rd and the subtractor 44 providing subtraction of output signal L,, from output signal LF' to provide difference signal Ld.

All of the summation and difference signals may be recorded on two physically separated tracks of a record disk using the conventional four-channel recording technique such as CD--4. It is also possible to provide broadcasting of the four-channel signals by feeding the summation and difference signals Ra, La, Rd and Ld to a four-channel broadcasting system known as Dorren system.

Modifications of the embodiment of Fig.

6 are illustrated in Figs. 8 and 9. The modification shown in Fig. 8 is generally similar to the Fig. 6 embodiment except that the right- and left-forward signals RF and LF are directly applied to the adders 41 and 42, respectively, so that signal Rp is algebraically combined with the signal R,, from adder 33 to drive the right speaker R with the combined output. Likewise, the signal LF is algebraically combined with the signal LBA from adder 34 to drive the left speaker L with the combined output. The nonprocessed, direct signal components RF and LF' when applied to the respective speakers, contribute to the creation of sonic images at the location of the respective speakers. The localization networks 12-3 and 124 are so adjusted that the original rear sound signals RB and LB are made to appear to origin ate from anywhere rightwardly of the right speaker R as at R' and from anywhere leftwardly of the left speaker L as at L', respectively.

The modification shown in Fig. 9 is also generally similar to the Fig. 6 embodiment except that the right and left-backward signals RB and LB are directly applied to the adders 41 and 42, respectively, so that signal RB is algebraically combined with the signal RFa from adder 31 to drive the right speaker R with the combined output. Likewise, the signal LB is algebraically combined with the signal LF,= to drive the left speaker L. In contrast with the embodiment of Fig. 8, the directly applied rearward signals RB and LB are used to localize their sonic images at the position of the respective speakers.The localization networks 12-1 and 12-2 are so adjusted that the forward signals RF and LF are made to appear to originate from anywhere between the speakers R and L as at R' and L'.

In the previous embodiments, two speakers are used for reproduction of a set of the processed or modified signals. In cases where it is desired to use four speakers for reproduction of the modified signals as processed in accordance with the previous embodiments, the listener would have an acousto-psychological impression different from what is originally intended to create using the non-modified stereophonic signals. Therefore, it is desirable to provide compatibility between two-speaker and four-speaker reproduction so that the modified stereophonic signals may also be reproduced through four speakers without creating the impression of a difference from what is originally intended by designers or program producers.

Figs. 10, 11 and 12 are illustrations of second embodiments of the invention which are intended for use in four-speaker reproduction of the stereophonic signals modified in accordance with the embodiments of Figs. 6, 8 and 9, respectively, and in which like parts are identified with like numerals throughout.

In Fig. 10, the system is divided into a recording section which is identical with the embodiment of Fig. 6 with the exception that matrix circuit 40 of Fig. 7 is employed, and a reproducing section which includes a matrix circuit 60 to convert the output signals from the recording section into the original Rpa, LFcr, RBa and LBcr As illustrated, the matrix circuit 60 includes an adder 61 to provide summation of the additive signal Ra (=RF, +RB ) and the difference signal Rd (=RF RB, ) to deliver a signal 2RFcr which is attenuated by attenuator 71 to one half of its input level so that signal RFa is derived.In the same fashion, a series circuit including adder 62 and attenuator 72 delivers a signal LF,. The signals For and LF" are applied to binaural localization networks 12-5 and 12-6, respectively, where the input signals are individually processed and then applied to crosstalk cancellation circuits 145 -- and 146, respectively. The output circuits of the cancellation networks 14--5 and 146 are connected to adders 81 and 82 in the same configuration as the output circuits of the cancellation networks 144 and 14 are connected to the adders 31 and 32.The binaural localization networks 12-5 and 12-6 are so designed that the output signals from the adders .81 and 82 respectively correspond to the original forward stereophonic signals RF and LF. The outputs from the adders 81 and 82 are amplified at 91 and 92, respectively, and fed to a rightforward speaker 101 and a left-forward speaker 102, respectively. The matrix circuit 60 further includes a pair of subtractors 63 and 64, the subtractor 63 providing subtraction of the difference signal Rd from the summation signal Ra to derive a signal 2RBer which is attenuated to one half of its magnitude by attenuator 73.

Likewise, the subtractor 64 provides subtraction of the difference signal Ld from the summation signal La to derive 2LBA which is attenuated to one half of its magnitude by attenuator 74. The signals RB and LB < r are applied to binaural localization networks 12-7 and 12-8 and thence to crosstalk cancellation networks 147 7 and 14--8, respectively. The output signals from the cancellation networks 121 7 and 14 8 are connected to adders 83 and 84 in the same manner as described above.The binaural localization networks 12-7 and 12-8 are so designed that the output signals of adders 83 and 84 correspond to original backward stereophonic signals RB and L,, respectively. The outputs from the adders 83 and 84 are applied through amplifiers 93 and 94 to a right-sideway speaker 103 and a left-sideway speaker 104, respectively. It is thus appreciated that the speakers 101 through 104 are fed with individual signals which correspond to the original signals so that sonic images are created in the same locations as would be created if the original signals were directly applied to the speakers.

Consider now a situation in which twochanneled stereophonic signals are reproduced using the reproduction section of the embodiment of Fig. 10. In this case, a right signal R is applied to input terminal 53 instead of signals Ra and Rd and a left signal L is applied to input terminal 54 instead of signals La and Ld. It will be appreciated that the output signals from the attenuators 71, 72, 73 and 74 correspond respectively to signals R/2, L/2, R/2, L/2.

Therefore, the stereophonic signals R and L from attenuators 71 and 72 are modified by the later stages in the same manner as described above to energize the front speakers 101 and 102, respectively.

Likewise, the other set of stereophonic signals from attenuators 73 and 74 are modified by the networks 12-7, 12-8 and 14-7, 14-8 to energize the sideway speakers 103 and 104.

Assume that the front-right and front-left speakers 101 and 102 are located at 20 degrees to the right and left of the centre line of the listener, respectively, and that the right and left sideway speakers 103 and 104 are located at 60 degrees to the right and left of the centre line, respectively, the sonic image of the signal RFα;, can be located at a 30-degree point to the right of the centre line by the speakers 101 and 102 by appropriately selecting the parameters of the networks 12-5 and l#5 and the sonic image of the signal LFA can be located at a 30-degree point to the left of the centre line by the same speakers 101 and 102 by appropriately selecting the parameters of the networks 12--6 and 146. Similarly, by suitable selecting of the parameters of the networks 12-7, 12-8, 147 and 14--8, the locations of the sonic images of signals RB < , and I, can be made to coincide with the locations of the sonic image attributable to signals RFa and LFa, respectively, by the right and left sideway speakers 103 and 104.

Since RFa and LFCr are equal to R/2 and Rna and LBC, are equal to L/2, the right and left channel signals are made to appear to origin ate respectively from the same locations as one would hear in a twochannel reproduction system.

In the embodiment of Fig. 11, forwardright and left signals RF and LF are directly applied to the matrix circuit 40, while the backward-right and left signals RB and LB are modified by the binaural localization networks 12-3 and 12-4 and the crosstalk cancellation networks 14--3 and 144, respectively, to derive outputs which are combined in adders 33 and 34 to derive signals RBα and LB, in the same manner as previously described with reference to the embodiment of Fig. 8.It is seen that the output signals from adders 41 and 42 of the matrix. 40 are a summation of RF and RBα and a summation of LF and LBa, respectively, and that the output signals from subtractors 43 and 44 are a difference between Rp and RB, and a difference between LF and Lna, respectively.

In the reproducing section of ths system, the matrix 60 performs the conversion of the input signals applied from the matrix 40 of the recording section into a set of signals corresponding to the input signals of the matrix 40, so that right- and left-forward speakers 101 and 102 are fed with signals RF and LF respectively. On the other hand, the signals RBα and LBEV from the matrix 60 are processed by binaural localization networks 12-7, 12-8 and crosstalk cancellation networks 14-7, 14--8 and through adders 83, 84 to derive signal R and LB, respectively, for energization of right- and left-backward speakers 103 and 104.

Fig. 12 is an alternative embodiment of the invention in which the right- and leftbackward signals RB and LB are directly applied to the matrix 40, while the right- and left-backward signals RF and LF are modified in the recording section in the same manner as described in connection with the embodiment of Fig. 9. In the reproducing section, the matrix 60 delivers signals Rfα and LF to binaural localization networks 12-5, 12-6 and crosstalk cancellation networks 14--5, 146, and through adders 81, 82 to derive signals corresponding to RF and LF at the output of adders 81 and 82, respectively, for application to the speakers 101 and 102.The matrix 60 also delivers signals corresponding to RB and LB for application to speakers 103 and 104.

Fig. 13 is an illustration of a third embodiment of the invention incorporating the basic functional blocks as previously described to permit two loudspeakers to reproduce four-channelled stereophonic signals. Original right- and left-forward signals RF and LF are applied to binaural localization networks 12-1 and 12-2, respectively, and thence to crosstalk cancellation circuits 141 and 142, respectively, as in the first embodiment, to derive a pair of signals RFr and RFI from the network 14I and a pair of signals L and LFI from the network 142. Similarly, the original right- and left-backward signals RB and LB are applied to binaural localization networks 12-3 and 12--4 respectively and thence to crosstalk cancellation networks 14--3 and 14--4 to deliver a pair of signals RBr and RBI from the network 14--3 and a pair of signals LBr and LBI from the network 144. An adder 111 is provided which receives the rightward components of the outputs from the networks 14--1 to 144 to accomplish summation of signals RFr, LFr, RBr and LBr. Likewise, an adder 112 is provided to accomplish summation of signals RFI, LFl, RBI and LBl. The summation outputs from the adders 111 and 112 are applied through amplifiers 121 and 122 to right and left speakers R and L, respectively. As described previously, the summation outputs may be recorded into a suitable recording medium or transmitted over a suitable transmission medium such as radio broadcasting channel.

Assume that the speakers R and L are respectively located at 30 degrees to the right and left of the centre line of a listener, the signal RF is made to appear to originate from a 20-degree point to the right of the centre line by the speakers R and L by appropriately selecting the parameters of the networks 12-1 and 1v1 and the signal LF is made to appear to originate from a 20degree point to the left of the centre line by the speakers R and L by appropriately selecting the parameters of the networks 12-2 and 142. Likewise, the signals RB and LB can be made to appear to originate from 60-degree points to the right and left of the centre line, respectively, by suitably selecting the parameters of the networks 12-3, 12-4, and 14-3 and 14-4.

Therefore, the same acoustic sensation can be obtained as one would experience when the quadraphonic signals are reproduced by the use of four speakers.

The embodiment of Fig. 13 can be modified in various ways as illustrated in Figs. 14--16 which are generally similar to the Fig. 13 embodiment with the exception that one or more of the cascaded circuits of the binaural localization network and crosstalk cancellation network is omitted to permit direct connection of one or more of the original stereophonic signals to an adder circuit. In Fig. 14, binaural localization network 12-1 and crosstalk cancellation network 14I are omitted to permit direct connection of the right-forward signal RF to the adder 111. With this arrangement, the right-forward signal is made to localize its sonic image at the position of the right speaker R and the other signals are made to localize their sonic images at positions other than the positions of the speakers R and L.

In Fig. 15, the right- and left-forward signals RF and LF are directly applied to adders 111 and 112, respectively, to localize sonic images at the positions of the speakers R and L, while the right- and left-backward signals RB and It, are modified to localize sonic images at any desired positions. The modification of Fig. 16 is to localize the right- and left-backward signals RB and LB in the positions of the speakers and the right- and left-forward signals RF and LF are used to localize at any desired positions.

Fig. 17 is an illustration of a fourth embodiment of the invention in which the two-channelled signal output of the embodiment of Fig. 13 is used to operate four speakers to reproduce the original four-channel stereophonic signals. The output from the adder 111 of Fig. 13 is applied to binaural localization networks 12-5 and 12-7 and the output from the adder 112 of Fig. 13 is applied to binaural localization networks 126 and 12-8. As mentioned in the previous embodiments, these signals are processed through the associated crosstalk cancellation networks.

Adders 81 to 84 provides summation of the outputs for the cancellation networks in the same manner as described previously to energize speakers 101 through 104, respectively. The localization networks 12-5, 126, 12-7 and 12-8 are so designed that there result in the outputs of the adders 81 through 84 signals which correspond to the original signals R L RB and LB. The circuit arrangement shown in Fig. 17 can also be used to reproduce the conventional two-channels stereophonic signals by suitably adjusting the binaural networks 12-5 through 12-8 so as to localize sonic images at any desired to positions.For example, by arranging the speakers 101 through 104 as illustrated in Fig. 19, the sonic image associated with the right signal can be created anywhere between the speakers 101 and 103 and the sonic image associated with the left signal can be created anywhere between the speakers 102 and 104.

Fig. 18 is a modification of the embodiment of Fig. 17, in which the two channelled signal output of the embodiment of Fig. 15 is used to operate four speakers.

The output from the adder 111 of the Fig. 15 embodiment is applied on the one hand directly to speaker 101 via amplifier 91 and on the other hand to binaural localization network 12-7 and thence to crosstalk cancellation network 144. The output from the adder 112 of the Fig. 15 embodiment is applied on the one hand to speaker 102 via amplifier 92 and on the other hand to binaural localization network 12-8 and thence to crosstalk cancellation network 146. Adders 83 and 84 provide summation of the outputs of the cancellation networks 14 7 and 14--8 as in the previous manner to drive speakers 103 and 104 respectively via amplifiers 93 and 94.In this circuit arrangement, the sonic images associated with the right and left original signals RF and It, are respectively localized at the position of the right and left speakers 101 and 102, while the other localized signals are made to appear to originate from any desired positions.

WHAT WE CLAIM IS: 1. Apparatus for modifying four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising: first binaural localization network means receptive of signals from a first signal source for developing a first binaural representation of said first signal, said first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of signals from a second signal source for developing a second binaural representation of said second signal, said second binaural representation consisting of first and second binaurally

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the networks 12-1 and 1v1 and the signal LF is made to appear to originate from a 20degree point to the left of the centre line by the speakers R and L by appropriately selecting the parameters of the networks 12-2 and 142. Likewise, the signals RB and LB can be made to appear to originate from 60-degree points to the right and left of the centre line, respectively, by suitably selecting the parameters of the networks 12-3, 12-4, and 14-3 and 14-4. Therefore, the same acoustic sensation can be obtained as one would experience when the quadraphonic signals are reproduced by the use of four speakers. The embodiment of Fig. 13 can be modified in various ways as illustrated in Figs. 14--16 which are generally similar to the Fig. 13 embodiment with the exception that one or more of the cascaded circuits of the binaural localization network and crosstalk cancellation network is omitted to permit direct connection of one or more of the original stereophonic signals to an adder circuit. In Fig. 14, binaural localization network 12-1 and crosstalk cancellation network 14I are omitted to permit direct connection of the right-forward signal RF to the adder 111. With this arrangement, the right-forward signal is made to localize its sonic image at the position of the right speaker R and the other signals are made to localize their sonic images at positions other than the positions of the speakers R and L. In Fig. 15, the right- and left-forward signals RF and LF are directly applied to adders 111 and 112, respectively, to localize sonic images at the positions of the speakers R and L, while the right- and left-backward signals RB and It, are modified to localize sonic images at any desired positions. The modification of Fig. 16 is to localize the right- and left-backward signals RB and LB in the positions of the speakers and the right- and left-forward signals RF and LF are used to localize at any desired positions. Fig. 17 is an illustration of a fourth embodiment of the invention in which the two-channelled signal output of the embodiment of Fig. 13 is used to operate four speakers to reproduce the original four-channel stereophonic signals. The output from the adder 111 of Fig. 13 is applied to binaural localization networks 12-5 and 12-7 and the output from the adder 112 of Fig. 13 is applied to binaural localization networks 126 and 12-8. As mentioned in the previous embodiments, these signals are processed through the associated crosstalk cancellation networks. Adders 81 to 84 provides summation of the outputs for the cancellation networks in the same manner as described previously to energize speakers 101 through 104, respectively. The localization networks 12-5, 126, 12-7 and 12-8 are so designed that there result in the outputs of the adders 81 through 84 signals which correspond to the original signals R L RB and LB. The circuit arrangement shown in Fig. 17 can also be used to reproduce the conventional two-channels stereophonic signals by suitably adjusting the binaural networks 12-5 through 12-8 so as to localize sonic images at any desired to positions.For example, by arranging the speakers 101 through 104 as illustrated in Fig. 19, the sonic image associated with the right signal can be created anywhere between the speakers 101 and 103 and the sonic image associated with the left signal can be created anywhere between the speakers 102 and 104. Fig. 18 is a modification of the embodiment of Fig. 17, in which the two channelled signal output of the embodiment of Fig. 15 is used to operate four speakers. The output from the adder 111 of the Fig. 15 embodiment is applied on the one hand directly to speaker 101 via amplifier 91 and on the other hand to binaural localization network 12-7 and thence to crosstalk cancellation network 144. The output from the adder 112 of the Fig. 15 embodiment is applied on the one hand to speaker 102 via amplifier 92 and on the other hand to binaural localization network 12-8 and thence to crosstalk cancellation network 146. Adders 83 and 84 provide summation of the outputs of the cancellation networks 14 7 and 14--8 as in the previous manner to drive speakers 103 and 104 respectively via amplifiers 93 and 94.In this circuit arrangement, the sonic images associated with the right and left original signals RF and It, are respectively localized at the position of the right and left speakers 101 and 102, while the other localized signals are made to appear to originate from any desired positions. WHAT WE CLAIM IS:

1. Apparatus for modifying four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising: first binaural localization network means receptive of signals from a first signal source for developing a first binaural representation of said first signal, said first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of signals from a second signal source for developing a second binaural representation of said second signal, said second binaural representation consisting of first and second binaurally

correlated signals which localize a binaural sonic image at a second location; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said - loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to provide a first additive output signal; second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to provide a second additive output signal;; first algebraically combining means to provide summation of said first additive output signal and signals from a third signal source; and second algebraically combining means to provide summation of said second additive output signal and signals from a fourth signal source.

2. Apparatus as claimed in claim 1, wherein said third and fourth signal sources comprises: third binaural localization network means receptive of signals from a signal source for developing a third binaural representation of the received signal, said third binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a third location; fourth binaural localization network means receptive of signals from a signal source for developing a fourth binaural representation of the received signal, said fourth binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a fourth location;; third crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said third binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; fourth crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said fourth binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; third additive network means receptive of said third signals from said third and fourth binaural localization network means to provide a third additive output signal which is said signals from said third signal source; and fourth additive network means receptive of said fourth signals from said third and fourth binaural localization network means to provide a fourth additive output signal which is said signals from said fourth signal source.

3. Apparatus as claimed in claim 1, further comprising: third algebraically combining means for providing a signal representative of the difference between said first additive output signal and signals from said third source; and fourth algebraically combining means for providing a signal representative of the difference between said second additive output signal and signals from said fourth source.

4. Apparatus as claimed in claim 2, further comprising: third algebraically combining means for providing a signal representative of the difference between said first additive output signal and said third additive output signal; and fourth algebraically combining means for providing a signal representative of the difference between said second additive output signal and said fourth additive output signal.

5. Apparatus as claimed in any preceding claim wherein each of said localization network means comprises: means receptive of the respective sound source signal and having a frequency characteristic determined in relation to the location of said sonic image to develop said first binaurally correlated signal; and means receptive of said first binaurally correlated signal and having a frequency response characteristic representing the difference in intensity and propagation time over the frequency range of said first binaurally correlated signal between a first and a second hypothetical acoustic signal which would be received at respective ears of a listener from said localized sonic image if he were seated with respect thereto, to thereby develop said second binaurally correlated signal.

6. Apparatus as claimed in any preceding claim, wherein each of said crosstalk cancellation network means comprises: first and second subtractors each having positive and negative input terminals and an output terminal, the positive input terminal of the first subtractor being receptive of said first binaurally correlated signal, the positive input terminal of said second subtractor being receptive of said second binaurally correlated signal;; first and second filter-and-delay networks each having a transfer characteristic B/A wherein A represents a transmission characteristic over an acoustic path between a said loudspeaker and a said listener's ear nearer to said loudspeaker and B represents a transmission characteristic over an acoustic path between said loudspeaker and the listener's other ear, the first filter-and-delay network being receptive of said first binaurally correlated signal for application of its output signal to the negative input terminal of said first subtractor; and third and fourth filter-and-delay networks each having a transfer characteristic represented by T/A l-(B/A)2 the third filter-and-delay network being receptive of the output signal from the first subtractor and the fourth filter-and-delay network being receptive of the output signal from the second subtractor, the output signals from the third and fourth filter-anddelay networks being said third and fourth binaurally correlated signals.

7. Apparatus for reproducing fourchannel stereophonic signals including a first summation signal (Rf+Rb), a second summation signal (Lf+Lb), a first difference signal (Rf-Rb) and a second difference signal (Lf-Lb) using a set of four loudspeakers arranged in spaced relation to each other, comprising:: means for converting said first and second summation signals and said first and second difference signals to develop a set of signals Rf, Lf, Rb and Lb; first binaural localization network means receptive of said signal Rf (or Rb) for developing a first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of said signal Lf (or Lb) for developing a second binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a second location;; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to provide a first additive output signal for energization of a first loudspeaker; second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to provide a second additive output signal for energization of a second loudspeaker;; means for applying said signals Rb (or Rf) and Lb (or Lf) to third and fourth loudspeakers, respectively.

8. Apparatus as claimed in claim 7, wherein said signal applying means comprises: third binaural localization network means receptive of said signal Rb (or Rf) for developing a third binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a third location; fourth binaural localization network means receptive of said signal Lb (or Lf) for developing a fourth binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a fourth location;; third crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said third binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; fourth crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said fourth binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; third additive network means receptive of said third signals from said third and fourth crosstalk cancellation network means to provide a third additive output signal to develop an output to energize said third loudspeaker; and fourth additive network means receptive of said fourth signals from said third and fourth crosstalk cancellation network means to provide a fourth additive output signal to develop an output to energize said fourth loudspeaker.

9. Apparatus for modifying four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising: first binaural localization network means receptive of signals from a first signal source for developing a first binaural representation of said first signal, said first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of signals from a second signal source for developing a second binaural representation of said second signal, said second binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a second location;; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means and signals from a third signal source to develop a first additive output signal; and second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means and signals from a fourth signal source to develop a second additive output signal.

10. Apparatus as claimed in claim 9, wherein said third signal source comprises: third binaural localization network means receptive of signals from a signal source for developing a third binaural representation of the received signal, said third binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a third location;; third crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said third binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers, said third binaurally correlated signal of the last-mentioned crosstalk cancellation network means being applied to said first additive network means and said fourth binaurally correlated signal of the last-mentioned crosstalk cancellation network means being applied to said second additive network means.

11. Apparatus as claimed in claim 10, wherein said fourth signal source comprises: fourth binaural localization network means receptive of signals from a signal source for developing a fourth binaural representation of the received signal, said fourth binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a fourth location;; fourth crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said fourth binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers, said third binaurally correlated signal of the last-mentioned crosstalk cancellation network means being applied to said first additive network means and said fourth binaurally correlated signal of the last-mentioned crosstalk cancellation network means being applied to said second additive network means.

12. Apparatus as claimed in any one of claims 7 to 11, wherein each of said localization network means comprises: means receptive of the respective sound source signal and having a frequency characteristic determined in relation to the location of said sonic image to develop said first binaurally correlated signal; and means receptive of said first binaurally correlated signal and having a frequency response characteristic representing the difference in intensity and propagation time over the frequency range of said first binaurally correlated-signal between a first and a second hypothetical acoustic signal which would be received at respective ears of a listener from said localized sonic image if he were seated with respect thereto, to thereby develop said second binaurally correlated signal.

13. Apparatus as claimed in any one of claims 7 to 12 wherein each of said crosstalk cancellation network means comprises: first and second subtractors each having positive and negative input terminals and an output terminal, the positive input terminal of the first subtractor being receptive of said first binaurally correlated signal, the positive input terminal of said second subtractor being receptive of said second binaurally correlated signal;; -first and second filter-and-delay networks each having a transfer characteristic B/A wherein A represents a transmission characteristic over an acoustic path between a said loudspeaker and a said listener's ear nearer to said loudspeaker and B represents a transmission characteristic over an acoustic path between said loudspeaker and the listener's other ear, the first filter-and-delay network being receptive of said first binaurally correlated signal for application of its output signal to the negative input terminal of said first subtractor; and third and fourth filter-and-delay networks each having a transfer characteristic represented by T/A l-(B/A)2 the third filter-and-delay network being receptive of the output signal from the first subtractor and the fourth filter-and-delay network being receptive of the output signal from the second subtractor, the output signals from the third and fourth filter-anddelay networks being said third and fourth binaurally correlated signals.

14. Apparatus for reproducing the signals modified in accordance with claim 9 using a set of four loudspeakers, comprising: first binaural localization network means receptive of said first additive output signal for developing a first representation of said first additive output signal, said first binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a first location; second binaural localization network means receptive of said second additive output signal for developing a second representation of said second additive output signal, said second binaural representation consisting of first and second binaurally correlated signals which localize a binaural sonic image at a second location;; first crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said first binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; second crosstalk cancellation network means receptive of said first and second binaurally correlated signals developed by said second binaural localization network means for developing third and fourth binaurally correlated signals which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to energize a first loudspeaker; and second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to energize a second loudspeaker, said first and second additive output signals being further applied to third and fourth loudspeakers, respectively.

15. Apparatus for reproducing the signals modified in accordance with claim 11, comprising: first and second binaural localization network means receptive of said first and second additive output signals respectively for developing first and second binaural representations of said received first and second additive output signals respectively, each of said first and second binaural representations consisting of a set of first and second binaurally correlated signals which localize binaural sonic images at first and second locations, respectively;; first and second crosstalk cancellation network means receptive of a respective set of said first and second binaurally correlated signals developed by said first and second binaural localization network means for developing a first set of third and fourth binaurally correlated signals and a second set of third and fourth binaurally correlated signals, respectively, each set of which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers;; third and fourth binaural localization network means receptive of said first and second additive output signals respectively for developing first and second binaural representations of said received first and second additive output signals respectively, each of said first and second binaural representations consisting of a set of first and second binaurally correlated signals which localize binaural sonic images at third and fourth locations, respectively;; third and fourth crosstalk cancellation network means receptive of a respective set of said first and second binaurally correlated signals developed by said third and fourth binaural localization network means for developing a third set of third and fourth binaurally correlated signals and a fourth set of third and fourth binaurally correlated signals, respectively, each set of which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to develop an output to energize a first loudspeaker;; second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to develop an output to energize a second loudspeaker; third additive network means receptive of said third signals from said third and fourth crosstalk cancellation network means to develop an output to energize a third loudspeaker; and fourth additive network means receptive of said fourth signals from said third and fourth crosstalk cancellation network means to develop an output to energize a fourth loudspeaker.

16. Apparatus for reproducing the signals modified in accordance with claim 4 using a set of four loudspeakers, comprising: means receptive of signals from the output of said first, second, third and fourth algebraically combining means for recovering said first, second, third and fourth additive output signals; first and second binaural localization network means receptive of said recovered first and second additive output signals respectively for developing first and second binaural representations of said received first and second additive output signals respectively, each of said first and second binaural representations consisting of a set of first and second binaurally correlated signals which localize binaural sonic images at first and secpnd locations, respectively;; first and second crosstalk cancellation network means receptive of a respective set of said first and second binaurally correlated signals developed by said first and second binaural localization network means for developing a first set of third and fourth binaurally correlated signals and a second set of third and fourth binaurally correlated signals, respectively, each set of which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; ; third and fourth binaural localization network means receptive of said recovered third and fourth additive output signals respectively for developing first and second binaural representations of said received third and fourth additive output signals respectively, each of said first and second binaural representations consisting of a set of first and second binaurally correlated signals which localize binaural sonic images at third and fourth locations, respectively;; third and fourth crosstalk cancellation network means receptive of a respective set of said first and second binaurally correlated signals developed by said third and fourth binaural localization network means for developing a third set of third and fourth binaurally correlated signals and a fourth set of third and fourth binaurally correlated signals, respectively, each set of which, when applied to loudspeakers, will produce no acoustic crosstalk which might be perceptible by a listener if the lastmentioned first and second binaurally correlated signals were supplied directly to said loudspeakers; first additive network means receptive of said third signals from said first and second crosstalk cancellation network means to develop an output to energize a first loudspeaker;; second additive network means receptive of said fourth signals from said first and second crosstalk cancellation network means to develop an output to energize a second loudspeaker; third additive network means receptive of said third signals from said third and fourth crosstalk cancellation network means to develop an output to energize a third loudspeaker; and fourth additive network means receptive of said fourth signals from said third and fourth crosstalk cancellation network means to develop an output to energize a fourth loudspeaker.

17. A recording medium in which signals from the first and second algebraically combining means as claimed in claim 1 are recorded on separate channels.

18. A recording medium in which said first and second additive output signals from said first and second additive network means as claimed in claim 9 are recorded on separate channels.

19. A method for processing four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising the steps of: modifying signals from a first signal source to develop a first pair of first and second binaurally correlated signals which render said first signal to appear to originate from a first location; modifying signals from a second signal source to develop a second pair of first and second binaurally correlated signals which render said second signal to appear to originate from a second location;; modifying said first pair of first and second binaurally correlated signals to develop a first pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said first pair of first and second binaurally correlated signals were directly used to produce sounds; modifying said second pair of first and second binaurally correlated signals to develop a second pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said second pair of first and second binaurally correlated signals were directly used to produce sounds providing summation of said third signals of said first and second pairs to produce a first additive output signal;; providing summation of said fourth signals of said first and second pairs to produce a second additive output signal; providing summation of said first additive output signal and signals from a third signal source to produce a first localized output signal; and providing summation of said second additive output signal and signals from a fourth signal source to produce a second localized output signal.

20. A method as claimed in claim 19, wherein said signals from said third and fourth signal sources are produced by the steps of: modifying signals from a signal source to develop a third pair of first and second binaurally correlated signals which render said signals from the last-mentioned signal source to appear to originate from a third location; modifying signals from a signal source to develop a fourth pair of first and second binaurally correlated signals which render said signals from the last-mentioned signal source to appear to originate from a fourth location;; modifying said third pair of first and second binaurally correlated signals to develop a first pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said third pair of first and second binaurally correlated signals were directly used to produce sounds modifying said fourth pair of first and second binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said fourth pair of first and second binaurally correlated signals were directly used to produce sounds providing summation of said third signals of said third and fourth pairs to produce a third additive output signal which corresponds to said signals from said third signal source; and providing summation of said fourth signals of said third and fourth pairs to produce a fourth additive output signal which corresponds to said signals from said fourth signal source.

21. A method as claimed in claim 19 or 20, further comprising the step of recording said first and second localized signals on separate channels of a recording medium.

22. A method as claimed in claim 19 or 20, further comprising the step of transmitting said first and second localized signals on separate carrier signals.

23. A method as claimed in claim 19, further comprising the steps of: generating a third localized output signal representative of the difference between said first additive output signal and signals from said third source; and generating a fourth localized output signal representative of the difference between said second additive output signal and signals from said fourth source.

24. A method as claimed in claim 20, further comprising the steps of: generating a third localized output signal representative of the difference between said first additive output signal and said third additive output signal; and generating a fourth localized output signal representative of the difference between said second additive output signal and said fourth additive output signal.

25. A method as claimed in claim 23 or 24, further comprising the step of recording said first, second, third and fourth localized output signals on separate channels.

26. A method as claimed in claim 23 or 24, further comprising the step of transmitting said first, second, third and fourth localized output signals on separate carrier signals.

27. A method for processing four-channel stereophonic signals into a form suitable for reproduction on two-speaker systems, comprising the steps of: modifying signals from a first signal source to develop a first pair of first and second binaurally correlated signals which render said first source signal to appear to originate from a first location; modifying signals from a second signal source to develop a second pair of first and second binaurally correlated signals which render said second source signal to appear to originate from a second location;; modifying said first pair of first and second binaurally correlated signals to develop a first pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said first pair of first and second binaurally correlated signals were directly used to produce sounds; modifying said second pair of first and second binaurally correlated signals to develop a second pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said second pair of first and second binaurally correlated signals were directly used to produce sounds; providing summation of said third binaurally correlated signals and signals from a third signal source to develop a first additive output signal; and providing summation of said fourth binaurally correlated signals and signals from a fourth signal source to develop a second additive output signal.

28. A method as claimed in claim 27, wherein said signals from said third signal source are generated by the steps of: modifying signals from a signal source to develop a third pair of first and second binaurally correlated signals which render said signals from the last-mentioned signal source to appear to originate from a third location; and modifying said third pair of first and second binaurally correlated signals to develop a third pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said third pair of first and second binaurally correlated signals were directly used to produce sounds.

29. A method as claimed in claim 28, wherein said signals from said fourth signal source are generated by the steps of: modifying signals from a signal source to develop a fourth pair of third and fourth binaurally correlated signals which render said signals from the last-mentioned signal source to appear to originate from a fourth location; and modifying said fourth pair of third and fourth binaurally correlated signals which, when used to produce sounds, will produce no acoustic crosstalk which might be perceptible by a listener if said fourth pair of first and second binaurally correlated signals were directly used to produce sounds.

30. A method as claimed in claim 27, 28 or 29, further comprising the steps of recording said first and second additive output signals on separate channels.

31. A method as claimed in claim 27, 28 or 29, further comprising the step of transmitting said first and second additive output signals on separate carrier signals.

32. Apparatus for modifying four-channel stereophonic signals into a form suitable for two-speaker reproduction substantially herein described with reference to Figs. 1, 6--9 of the accompanying drawings.

33. Apparatus for reproducing fourchannel stereophonic signals substantially herein described with reference to Figs. 1, 11--12 of the accompanying drawings.

34. Apparatus for modifying four-channel stereophonic signals into a form suitable for two-speaker reproduction substantially herein described with reference to Figs. 1, 13-16 of the accompanying drawings.

35. Apparatus for reproducing fourchannel stereophonic signals substantially herein described with reference to Figs. 1, 17 and 18 of the accompanying drawings.

36. A method for processing four-channel stereophonic signals into a form suitable for two-speaker reproduction substantially herein described with reference to Figs. 1 69 of the accompanying drawings.

37. A method for processing four-channel stereophonic signals into a form suitable for two-speaker reproduction substantially herein described with reference to Figs. 1, 13-16 of the accompanying drawings.