JP2611233B2 - Amplitude compression / expansion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Field of application in industry B Outline of the invention C Conventional technology D Problems to be solved by the invention (FIGS. 13 to 15) E Means for solving the problems (FIG. 1) F operation (FIG. 1) 1) G embodiment (G1) Principle of the present invention (FIGS. 1 and 2) (G2) Amplitude compression / expansion operation (FIGS. 1, 3 to 6) (G3) Amplitude of variable frequency characteristics Compression / expansion operation (FIGS. 1, 7 to 9) (G4) First embodiment (FIGS. 1, 7 to 10) (G5) Second embodiment (FIG. 1, FIG. (FIGS. 11 and 12) (G6) Other Embodiments H Effect of the Invention A Industrial Field of the Invention The present invention relates to an amplitude compression / expansion circuit, for example, a signal of an electronic device such as a compact disk (CD) player and a tape recorder. It is suitable for application to a processing circuit.

B. Summary of the Invention In the present invention, in an amplitude compression / expansion circuit, a desired input signal is output by adding an output signal generated based on a difference signal between input and output signals of a main path circuit to an output signal of the main path circuit. An amplitude compression / expansion circuit having output characteristics can be obtained.

2. Description of the Related Art Conventionally, in a digital audio signal reproducing apparatus such as a CD player and a digital audio tape recorder (DAT), a digital signal recorded on a recording medium is reproduced and demodulated into an analog signal to reproduce a wide range. It is possible to obtain a high-quality audio signal with less distortion in a dynamic range.

D Problem to be Solved by the Invention However, the audio signal obtained from this kind of digital audio signal reproducing apparatus has a problem that the dynamic range is too wide when recording on a conventional analog tape recorder.

That is, when recording on a tape recorder because the dynamic range is too wide, there is a problem that the signal waveform of the audio signal is distorted in a portion where the signal level is large, or the SN ratio is deteriorated in a portion where the signal level is small. .

Furthermore, when a CD player or the like that has background noise is played, for example, in a car, the part with a small signal level cannot be heard due to the background noise, or the volume becomes too large at a part with a large signal level. Problem.

In order to solve this problem, it is considered that the dynamic range of the audio signal obtained from the digital audio signal reproducing device should be reduced.

That is, as shown in FIG. 13, for an input signal composed of an audio signal converted to an analog signal, for an input signal having a peak level of -30 [dB] or less, a proportional constant is proportional to a change in the signal level of the input signal. An output signal whose signal level changes in proportion to 1 is output.

On the other hand, for an input signal in the region exceeding -30 [dB], an output signal whose proportional constant changes in proportion to, for example, 1/2 with respect to a change in the signal level of the input signal is output.

In this way, the input / output characteristics of the amplitude compression ratio CR of values 1 and 2 can be obtained at a boundary of -30 [dB] (hereinafter referred to as a break point), and the audio signal of the audio signal can be obtained as a whole. The dynamic range can be reduced.

In order to obtain such an amplitude compression / expansion operation, the conventional 14th
There is a method using an amplitude compression / expansion circuit 1 having a configuration as shown in FIG.

That is, the input signal S _I via a delay circuit 2 with receiving the amplitude modulation circuit 3 receives the control signal generating circuit 4.

Control signal generating circuit 4 detects the signal level of the input signal, a control signal whose signal level varies according to the signal level of the input signal S _I on the basis of the detection result
And it outputs the S _G to the amplitude modulation circuit 3.

The amplitude modulation circuit 3 includes a multiplication circuit or a VCA (voltage contr
It consists of ol Amplifier) or the like, the input signal S _{by I} amplitude modulated by a control signal S _G, the input signal S output signal is the signal level changes according to the signal level of the control signal S _G against _I S ₀ Can be obtained.

Attributable to the delay circuit 2, Obashiyuto the output signal S ₀ of the amplitude compression expansion circuit 1 is provided so as not to cause.

Here, the amplitude value x of the input signal S _I, if put the amplitude of the output signal S ₀ and the value y, can represent the amplitude compression ratio CR by: ^{y = x 1 / CR ...... (} 1).

In accordance connexion control signal generating circuit 4, the amplitude x of the input signal S _I of the break point following areas, the amplitude compression ratio
Amplitude y of the output signal S ₀ of the CR value 1 is represented by the following formula ^{y = x 1 / CR = x} · x (1-CR) / CR = x · x 0 = x · 1 ...... (2) You. Accordingly, if the control signal _SG is output so that the gain g of the amplitude modulation circuit 3 becomes a value 1 expressed by the following equation g = 1 in accordance with the coefficient 1 on the right side, the signal is broken. In the region below the point, the characteristic that the amplitude compression ratio CR is 1 can be obtained.

Amplitude x of the input signal S _I above break point area contrast
Respect, if the amplitude compression ratio CR is obtained an output signal S ₀ of the value of 2, the following equation ^{y = x 1 / CR = x} · x (1-CR) / CR = x · x -1/2 ...... (4) g = x ^{(1−CR) / CR} = x− ^{1 / 2} (5) represents the amplitude y of the output signal S ₀ and the gain g of the amplitude modulation circuit 3.

Accordance connexion, if the output control No. S _G so that the gain g of the amplitude modulation circuit 3 becomes a value x ^-1/2, the amplitude compression ratio CR in the above point bending regions obtain the input and output characteristics of the values 2 Can be.

Specifically, it is considered that the control signal generation circuit 4 may be configured as shown in FIG.

That through the absolute value circuit 5 to the input signal S _I received in飽絡detection circuit 6 to obtain a detection signal S _L proportional to the signal level of the input signal S _I, after logarithmic transformation via a logarithmic transformation circuit 7,
Output to the addition circuit 9.

Clip circuit 8 receives a sum signal of detection signals S _L and broken point signal S _H to the logarithmic transformation is obtained through the addition circuit 9,
The value 0 or less of the sum signal to clip the 0 value and outputs the resulting clip signal S _CL to the multiplier circuit 10.

Thus by selecting a break point signal S _H to a predetermined value, it is possible to obtain the clip signal S _CL whose signal level changes in the signal level of the input signal S _I defined by the broken point signal S _H to the boundary.

Multiplier circuit 10, the clip signal S _CL under compressive proportional control signal S _P with, and outputs the multiplication output to the amplitude modulation circuit 3 composed of a multiplier circuit via the exponential conversion circuit 11.

Here the input signal S _I with respect to the signal level of the output signal outputted from the logarithmic converter circuit 7 when the peak level H, the broken point signal level value of the input signal S _I (in this case, -30 dB!) putting a Y, the following equation a broken point signal S _H Is set in the value represented, clip signal S whose signal level varies according to the signal level of only the input signal S _I is greater than the signal level of the bending point signal level of the input signal S _I
You can get _CL .

Therefore, the clip circuit 8 is applied to the area below the break point.
Through the clip has been clip signal S _CL is obtained a value 0, so that the exponential conversion circuit 11 control signal values 1 corresponding to the value 0 through S _G are output.

As a result, the gain of the multiplication circuit 3 is controlled to 1 and
Output signal with an amplitude compression ratio CR of 1 as shown in equation (2)
S ₀ can be obtained, and thus, the input / output characteristics with the amplitude compression ratio CR of 1 can be obtained.

On the other hand, (5)
Gain of the multiplier circuit 3 as shown in Equation may be such that the value x ^-1/2.

That is, the following equation ^{_{S G = x (1-CR}} ) / CR ...... (7) may be output control signal S _G of the signal level of the input signal S _I.

That gain A _p of the multiplier circuit 10 is the following equation Represented as a value in, if to apply a compression ratio control signal S _P, the output signal S ₀ which is amplitude compression in the compression ratio above the break point in the region CR (in this case CR = 2) Obtainable.

Thus the signal level of the input signal S _I increases -30
An amplitude compression / decompression circuit 1 having an input / output characteristic in which the value of the amplitude compression ratio CR changes from a value 1 to a value 2 at a signal level of [dB].
Can be obtained.

However, in this case, there is a problem that the amplitude compression ratio CR rapidly changes before and after the break point. Therefore, when the audio signal obtained through the amplitude compression / expansion circuit 1 is reproduced, the reproduced sound is extremely low. There is an unnatural problem.

To solve this problem, for example, ROM (read only mem
By gradually changing the signal level signal level accompaniment with broken point signal S _H and the compression ratio control signal S _P to the change of the input signal using the ory) table, the method of slowly varying amplitude compression ratio CR Conceivable.

And using a control circuit of the arithmetic processing circuitry in place of the ROM table, it is also considered a method for controlling the break point signal S _H and the compression ratio control signal S _P.

However, in this case, the configuration of the entire amplitude compression / expansion circuit becomes complicated, and there is a problem that it is still insufficient for practical use.

Further in such an amplitude compression and decompression circuit for the output signal S multiplied output signal S ₀ according to the control signal S _G obtained from the control signal generating circuit 4 as ₀ give only the frequency of the input signal operating characteristics There was a problem that could not be changed according to.

Especially, in the case of audio signals, if the operating characteristics of amplitude compression and expansion can be changed according to the frequency of the input signal, the amplitude-compressed audio signal can be corrected according to the sense of hearing to reduce the dynamic range. It can be widely applied to various fields such as reduction.

The present invention has been made in view of the above points, and has as its object to propose an amplitude compression / expansion circuit capable of obtaining desired input / output characteristics with a simple configuration as a whole.

Means for Solving E Problem In order to solve such a problem, in the present invention, the first output signal S ₀ is given by applying the first or second gain to the amplitude compression / expansion input signal S _I. The amplitude compression / expansion input signal
By switching the gain to be applied to the amplitude compression input signal S _I when has decreased to the signal level corresponding to the S _I or the first signal level break point of the output signal S ₀ from the first gain to a second gain, A first amplitude modulating means 3 for outputting a first output signal while switching an amplitude compression ratio before and after the break point;
First and subtracting means 21, third or fourth gain for the difference signal S _R to obtain a difference signal S _R of amplitude compression decompression input signal S _I and the first output signal S ₀ of the amplitude modulating means 3 grant obtain a second output signal, first amplitude modulating means a gain switched gain to be applied to simultaneously difference signal S _R of 3 third gain from the second output switches to the fourth gain A signal processing means for outputting a third output signal S _S based on the second output signal; a first amplitude modulation means for outputting a third output signal based on the second output signal; A second subtraction unit 25 that outputs a subtraction output of the output signal S _I and the third output signal S _S of the signal processing unit 26 as a fourth output signal S ₀₁ . pressure of an output signal S _01, the smooth elongation properties in accordance connexion signal level break point in the signal level of the amplitude decompression input signal S _I go high summer As the amplitude decompression output signal S ₀₁ as to shift the characteristics, so as to deliver.

F function The second amplitude modulation means 22 of the signal processing means 26 performs the first amplitude modulation on the difference signal S _R between the input signal S _I and the first output signal S ₀ of the first amplitude modulation means 3. Input signal at means 3
Grant gain that varies in the same way as the change in the gain applied to S _I, as a result the signal processing means the third output signal S _S generated by the 26 first amplitude modulation in the second subtraction means 25 It is subtracted from the first output signal S ₀ means 3.

The fourth output signal thus obtained by the second subtraction means 25
S ₀₁ is the first output signal S ₀ of the first amplitude modulating means 3 which has received the gain switching at the break point, and the second amplitude modulating means.
By being obtained as a result of subtraction from the second output signal at 22, the break point smoothly changes to the compression characteristic state through the expansion characteristic state.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

(G1) in a first diagram the same reference numerals are assigned to corresponding portions of the principle Figure 14 of the present invention, 20 as a whole represents the amplitude compression and expansion circuit, the input signal S _I and the output signal S of the multiplier circuit 3 ₀ receives the summing circuit 21 and supplies the difference signal S _R to the multiplier circuit 22.

Multiplier circuit 22 receives a control signal S _G with the difference signal S _R, filter circuit 23 and the amplification circuit the multiplication output signal
The signal is output to the adder circuit 25 via 24.

As the result the adder circuit 25, during amplitude compression operation gain of less than one multiplier circuit 3, the output signal S _S is phase reversed is obtained via the amplifier circuit 24 the output signal S _0, the output The added output of the signals S _S and S ₀ is the output signal of the amplitude compression / expansion circuit 20 (that is, the amplitude compression / expansion output signal) S ₀₁
Is sent as

Thus the amplitude compression and decompression circuit 20 includes a main path circuit constituted by the input signal (i.e. amplifying decompression input signal) S _I control signal S multiplier circuit 3 amplifies and outputs a gain corresponding to _G, the difference signal S _R is obtained, and this is processed by a signal processing circuit 26 comprising a multiplication circuit 22, a filter circuit 23 and an amplification circuit 24.
And a sub-pass circuit that outputs the signal through the sub-circuit.

In the above configuration, when the gain g of the multiplier circuit 3 is set to values of 1 or near, by the signal level of the difference signal S _R is a value of a value 0 or near, through the main path circuit output signal S ₀ is dominant output signal obtained Te
_S01 is output via the adding circuit 25.

In contrast, when the gain g of the multiplier circuit 3 is set to a value other than the value in the vicinity of one or the signal level of the sub connexion difference signal S _R to the signal level of the input signal S _I is high increases by the signal level of the output signal S _S obtained via the sub-path circuit increases, correspondingly the output signal S ₀₁
The ratio of the output signal S _S subpaths circuit occupied in by increases, the output signal S ₀₁ output is predominant subpaths circuit is obtained.

Therefore, the signal processing circuit 26 constituting the sub-path circuit accordingly.
Input-output characteristic by selecting the a predetermined value, the input signal S _I smooth the time has decreased to the signal level corresponding to the break point signal level accompaniment with the output signal S ₀₁ to the increase compression properties or stretch characteristics of A desired input / output characteristic that changes so as to exhibit

Here, the gains of the multiplication circuits 3 and 22 are respectively set to g,
Assuming that the transfer function of the filter circuit 23 is F (ω) and the gain of the amplifier circuit 24 is A, the output of the amplitude Z ₁ represented by the following equation via the multiplier circuit 3 is given by the following equation: Z ₁ = gx (9) signal S ₀ is obtained.

Through the results adding circuit 21, the formula _{Z R = Z 1 -x = gx} -x ...... can obtain a difference signal S _R of the amplifier Z _R of the formula (10), a signal processing circuit 26 Through the following equation, an output signal S _S of the amplified Z ₂ is obtained by the following equation: Z ₂ = g · A · F (ω) · Z _R = g · A · F (ω) · (gx−x) be able to.

Therefore, based on the equations (9) and (11), the following equation y ₁ = Z ₁ −Z ₂ = gx−g · A · F (ω) · (gx−x) = ｛ (1-F (ω) · a) -F (ω) · a · g} gx ...... it is possible to obtain an output signal S ₀₁ of the amplitude y ₁ represented by (12).

Here, when the amplitude x and the transfer function F (ω) are x = 1 and F
(Omega) = 1 Distant, changes when the gain g of the multiplier circuit 3 and 22 from the value 0 so as to vary between the values 1, and the signal level of the input signal S _I to the constant amplitude compression control signal S _G In this case, the output characteristics of the amplitude compression / expansion circuit 20 can be known.

That is, in the equation (12), the following equation F (ω) = 1 (13) x = 1 (14) and the following equation y ₁ = ｛(1 + A) + A · g｝ g (15) Obtainable.

At this time, as shown in FIG. 2, when the gain g is changed from a value of 0 to 1, when the gain g is a value of 0.5, the gain of the amplitude compression / expansion circuit 20 as a whole becomes maximum and the gain A of the amplifier circuit 24 becomes If it increases, it is possible to obtain an output characteristic in which the overall gain increases accordingly.

Further, when the gain g changes from the value 0 to the value 1 when the gain A is 0, the output characteristic of only the main path circuit whose gain increases linearly is obtained. Is a value other than 0, the gain of the sub-pass circuit is superimposed on the gain of the main-pass circuit, so that an output characteristic having an upper right slope can be obtained as a whole.

Thus, by controlling the gain of the subpath circuit, the gain of the entire amplitude compression / expansion circuit 20 can be controlled, and the output signal that changes with desired input / output characteristics by the provision of the subpath circuit with respect to the main path circuit can be controlled. S ₀₁ can be obtained.

(G2) Amplitude compression / expansion operation In the configuration of FIG.
By setting (ω) to a value of 1, it is possible to obtain an operation characteristic in which the amplitude compression ratio CR changes smoothly, and if the gain A of the amplifier circuit 24 is set to a predetermined value, the amplitude compression operation and the amplitude The extension operation can be realized at the same time.

Here, the break point is set to 0 [dB], and the amplitude compression ratio CR
Consider the case where is set to the value 2.

In this case, from equation (5), the gain g of the multiplying circuit 3 may be set to the value x ^−1/2 in the region above the break point, and accordingly, the gain of the multiplying circuit 22 is similarly set to the value x in the region above the break point. Set to ^-1/2 .

At this time, the break point following areas, the amplitude x _R of the difference signal S _R becomes equal to 0, based on the operation of the main path circuit, the input signal, as shown in FIGS. 3 and 4 S _I the output signal S ₀₁ in proportion to the obtained.

On the other hand, in the region above the break point, the following equation F (ω) = 1 (16) g = x− ^{1 / 2} (17) is substituted into the equation (12), and the following equation y ₁ = ｛(1−A) −A · x ^−1/2 ｝ x ⁻¹ / ² · x = (1−A) · x ^−1/2 −A (18)

In the vicinity of this gain A is 1, increasing beyond the break point signal level of the input signal S _I, which accompanied connexion gradually reduced change in the signal level of the output signal S _01, the amplitude compression ratio CR It can be seen that the value gradually becomes parallel to the value 2 (that is, the input / output characteristic represented by a straight line when the gain A is 0).

Accordingly, it is possible to obtain the input / output characteristic of the amplitude compression operation in which the amplitude compression ratio CR gradually changes from the value 1 to the value 2 after passing the break point.

On the other hand, the gain A is 3 to 10 (Fig. 3), 10 to 100
For (FIG. 4), by the change of the signal level of the output signal S ₀₁ is increased relative to the signal level of the input signal S _I past the break point, the amplitude compression ratio CR is higher than the value 1 from the value 1 After changing to a small value (that is, after the amplitude expansion operation is obtained), the input / output characteristic is gently parallel to the input / output characteristic represented by a straight line when the gain A is 0 (therefore, the amplitude compression ratio CR becomes 2). Input / output characteristics (such as exhibiting compression characteristics) can be obtained.

In this case, if the gain A increases, the change in the signal level due to the expansion characteristic increases accordingly.

Thus, be selected to a proper value according to the gain A need, realize amplitude compression expansion circuit such that a smooth transition between the elongation properties and the compression characteristics in response to changes in the signal level of the input signal S _I it can.

Next, considering the case where the amplitude compression ratio CR is further increased to a value of 100, CR = 100 is substituted into the equation (5), and the following equation g = x− ^{99 /} 100 (19) is obtained. getting can, by substituting this in place of the ^{x -1/2} (18) equation, the following equation _{y 1 = {(1-a} ) -A · x -99/100} x -99/100 · x = (1−A) x−1 / ¹⁰⁰⁻ A · x− ⁹⁹ / ¹⁰⁰ (20)

The output characteristics of after passing the break point of the output signal S ₀₁ of the case, FIG. 5 (A = 0) and Figure 6 (A = 10 to 10
As shown in (0), when the gain A is A = 0, almost no compression characteristic is produced, whereas when A = 2 to 10, the expansion characteristic (when the input level is low) is very smooth. The transition to the compression characteristic (when the input level is high) occurs, and when A = 10-100, the transition from the intense expansion characteristic to the compression characteristic occurs smoothly.

(G3) Amplitude compression / expansion operation of variable frequency characteristics The amplitude compression / expansion operation in the case of using a bandpass filter circuit having a frequency characteristic as shown in FIG. 7 as the filter circuit 23 in the configuration of FIG.

That is, the filter circuit 23 has a center frequency of 2 to 3 [kHz
z], and a band-pass filter circuit attenuating by 6 [dB / OCT].

In this case, if the gain A of the amplifier circuit 24 is set to a value 1 and the amplitude compression ratio CR is set to a value 2, the following equation is obtained from the equation (12): y ₁ = ｛(1 + F (ω))-F (ω) · x ^{− 1/2} · x -1/2 · x =} (1-F (ω)) · x 1/2 -F (ω) can be obtained a relationship ... (21).

Therefore, since the transfer function F (ω) is included in the first term on the right side, it is understood that the amplitude compression / expansion operation changes according to the frequency characteristic of the filter circuit 23.

That is, the case of increasing the signal level of the input signal S _I as shown in FIG. 8, 0 gently amplitude compression ratio CR in the boundary of the break point of the [dB] is changed in One suited to the value 2, and the It can be seen that the change changes with a delay as it approaches the center frequency f of the bandpass filter circuit.

Expressed case a further frequency axis as shown in FIG. 9 receives an input signal S _I of preparative connexion predetermined input level on the horizontal axis, depending on the frequency to around 15 [dB] with respect to the input signal S _I The amplitude compression / expansion operation changes and the input level is almost 20
It can be seen that the amplitude compression ratio CR becomes constant at a value of 2 in the range exceeding [dB].

Thus, it is possible to obtain the amplitude compression and expansion circuit 20 of input-output characteristic amplitude compression operation is changed according to the frequency of the input signal S _I.

(G4) First Embodiment In FIG. 1, the gain A of the amplifier circuit 24 is set to a value near 1, and the filter circuit 23 is provided with a center frequency of about 4 [kHz], which is the most sensitive to the sense of hearing. A bandpass filter circuit is used.

With this configuration, as described above with reference to FIGS. 8 and 9, it is possible to obtain input / output characteristics in which the amplification / compression ratio gradually changes at the break point as the signal level of the input signal increases. .

Therefore, it is possible to obtain an audio signal having a compressed dynamic range by preventing the unnaturalness occurring in the reproduced sound when the amplification compression ratio changes abruptly.

Furthermore it is possible to obtain different output characteristics of amplitude compression operation according to the frequency of the input signal S _I, the center frequency 4 [kHz frequency bandpass filter circuit of the input signal S _I accompanied connexion input signal S _I to the increase in ], The amplitude compression operation can be started with the latest delay.

Therefore, the dynamic range around the center frequency 4 [kHz] can be reduced as much as the whole as compared with the dynamic range at other frequencies.

Actually, as shown in FIG. 10, the human hearing sensation has the highest sensitivity at a frequency of about 4 [kHz], and a frequency of 4 [kHz].
Even if the dynamic range of frequency bands other than [z] decreases, reducing the decrease of the dynamic range in the frequency band around frequency 4 [kHz] reduces the dynamic range of the reproduced sound as a whole by the sense of hearing. The feeling of decrease can be reduced, and the feeling of decrease in the dynamic range can be audibly corrected.

Therefore, the dynamic range of the audio signal obtained from the digital audio signal reproducing apparatus can be reduced without causing unnaturalness, and the resulting reduction in the dynamic range of the auditory sense can be reduced. it can.

Thus, when listening to an audio signal obtained from a digital audio signal reproducing device in a place where there is background noise, when the volume cannot be increased and it is not possible to listen, it is possible to listen well and to record on a tape recorder. In addition, recording can be performed without causing deterioration of the SN ratio and waveform distortion.

According to the above configuration, the signal level of the input signal is increased by configuring the signal processing circuit using the amplification circuit, the multiplication circuit, and the bandpass filter circuit and selecting the gain of the signal processing circuit to a predetermined value. As a result, it is possible to obtain input / output characteristics in which the amplification / compression ratio changes gradually and the amplification / compression operation changes in accordance with the frequency of the input signal.

Accordingly, the dynamic range of an audio signal having a wide dynamic range can be compressed, and at the same time, the sense of decrease in the dynamic range can be reduced.

(G5) Second Embodiment In FIG. 1, a low-pass filter circuit is used in place of the band-pass filter circuit of the first embodiment.

With this configuration, as shown in FIG. 11, as the frequency of the input signal is higher, it is possible to obtain input / output characteristics in which the amplification / compression operation starts earlier in a region where the signal level of the input signal is lower.

Actually, as shown in FIG. 12, in the case of an analog type magnetic tape, as the frequency of the recording signal increases, even if the signal level of the recording signal increases by a predetermined value or more, the output level decreases due to self-demagnetization. There is a problem that decreases.

Therefore, as in this embodiment, as the frequency of the input signal increases, the recording signal is supplied to the magnetic head via an amplitude compression / expansion circuit in which the amplification / compression operation starts earlier as the signal level of the input signal increases. By doing so, it is possible to prevent a decrease in output level due to the self-demagnetizing action.

(G6) Other Embodiments (1) In the above-described embodiment, a case has been described in which a band-pass filter circuit and a low-pass filter circuit are used as the filter circuits. However, the present invention is not limited to this and may Accordingly, a high-pass filter circuit, a trap filter circuit, or the like may be used.

(2) In the above-described embodiment, the case where the amplitude compression operation is changed in accordance with the frequency of the input signal using the filter circuit has been described. However, the present invention is not limited to this, and the signal processing circuit is not limited to this. Only the multiplication circuit may be provided.

In this case, it is possible to obtain an amplitude compression / expansion circuit having input / output characteristics in which the amplitude compression ratio smoothly changes at the break point.

(3) Further, in the signal processing circuit, only an amplifier circuit may be provided, or only a filter circuit may be provided.

When only the amplifier circuit is provided, by selecting the gain of the amplifier circuit to a desired value, it is possible to obtain input / output characteristics in which the amplitude compression / expansion operation is performed only when the signal level of the input signal falls within the characteristic range. .

When only the filter circuit is used, when the signal level of the input signal changes and the signal level of the difference signal changes,
Since the signal level of the difference signal component added to the output signal of the main path circuit via the filter circuit changes accordingly, it is possible to obtain input / output characteristics whose frequency characteristics change according to the signal level of the input signal.

Accordingly, in this case, if a low-pass filter circuit is used for the filter circuit, the high-frequency component of the input signal can be emphasized. If a band-pass filter circuit is used instead, the band-pass filter circuit can be used. Signal components in the pass band of the circuit can be emphasized.

Therefore, even if only the filter circuit is used instead of the configuration of the first and second embodiments described above, an effect similar to that of the first and second embodiments can be obtained with a simple configuration as a whole.

(4) In the signal processing circuit, a clip circuit may be used. With this configuration, the output signal output from the signal processing circuit can be clipped at a predetermined signal level, so that a desired change can be given to the input / output characteristics of the amplitude compression / expansion circuit as a whole.

(5) In the signal processing circuit, a clipping circuit, an amplifying circuit, a multiplying circuit and a filter circuit may be used in combination as needed. Is set to a desired value, the input / output characteristics of the entire amplitude compression / expansion circuit can be selected to a desired characteristic.

(6) In the above-described embodiment, the case where the multiplication circuit is used as the amplitude modulation circuit has been described. However, the present invention is not limited to this, and the same effect as that of the above-described embodiment can be obtained by using a VCA or the like. Obtainable.

(7) In the first and second embodiments, the case where the amplitude compression ratio CR is set to the value 1 in the region below the break point has been described. However, the present invention is not limited to this, and the region below the break point is not limited to this. May be set to a value other than the value 1.

In this case, if an input signal having a signal level equal to or higher than the break point is input, if a difference signal is obtained in the signal processing circuit, the amplification compression ratio can be smoothly changed to a desired amplitude compression ratio from the amplification compression ratio at the break point. A changing input / output characteristic can be obtained.

(8) Further, in this case, the amplitude compression ratio CR is set to a value of 1
By setting as follows, it is possible to obtain the amplitude extension operation in the area below the break point, and to obtain the input / output characteristics that gradually change from the amplitude extension operation to the amplitude compression operation at the break point.

(9) If the gain A of the amplifier circuit is set to a value of 2 or more and only the region above the break point is used, the amplitude compression ratio control from the amplitude expansion operation of the amplitude compression ratio CR according to the value of the gain A can be performed. it is possible to obtain the input and output characteristics that change slowly in amplitude compression operation of the amplitude compression ratio CR determined by the signal S _G.

(10) Further, in the above-described embodiment, the case where the control signal is created based on the signal level of the input signal of the multiplication circuit 3 as the amplitude modulation circuit has been described, but the present invention is not limited to this, and the present invention is not limited to this. The present invention can also be applied to an amplitude compression / expansion circuit configured to generate a control signal based on a signal level.

(11) In the above embodiment, the present invention is applied to a signal processing circuit for an analog audio signal obtained from a digital audio signal reproducing apparatus and an analog recording signal supplied to a magnetic head of a tape recorder. As described above, the present invention is not limited to this, and can be widely applied to a case where the entire amplitude compression / expansion circuit is constituted by a digital circuit and the digitized input signal is subjected to amplitude compression / expansion processing.

(12) Further, in the above-described embodiment, the case where the recording signal supplied to the magnetic head is subjected to the amplitude compression / expansion processing using the low-pass filter circuit as the filter circuit has been described. However, the present invention is not limited to this, and the present invention is not limited to this. May be subjected to amplitude compression / expansion processing using a low-pass filter circuit.

In this case, since the input signal having a high frequency and a large signal level can be amplitude-compressed, for example, in a headphone stereo, the ear can be protected from the high-frequency large-amplitude reproduced sound and the reproduced sound can be protected. Can be prevented from leaking from the headphone to the surroundings.

(13) Further, in the digital audio signal processing apparatus, if an amplitude compression / expansion circuit using such a low-pass filter circuit is inserted before the encoding encoder circuit, for example, a female voice signal can be transmitted. It is possible to prevent the difficulty of hearing caused by quantization noise when reproducing a female rubbing sound or the like which is a vocal sound.

(14) Further, if the present invention is applied to an audio signal transmitted in a cable music broadcast, a transmission path, an encoder, and the like for simultaneously transmitting a plurality of audio signals using many channels can be simplified as a whole.

(15) In the above-described embodiments, the case where the present invention is applied to a digital audio signal reproducing apparatus and an analog tape recorder has been described. However, the present invention is not limited to this, and audio signals, audio signals, and video signals may be used. Etc. can be widely applied to amplitude compression / expansion circuits.

H Effects of the Invention As described above, according to the present invention, a difference signal obtained from an input / output signal of an amplitude modulation circuit is added to an output signal of the amplitude modulation circuit via a signal processing circuit having predetermined input / output characteristics. By outputting, an amplitude compression / expansion circuit having desired input / output characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an amplitude compression / expansion circuit according to the present invention, FIGS. 2 to 9 are characteristic curves for explaining the operation thereof, and FIG. 10 is a characteristic curve showing an equal loudness curve. 11 and 12 are characteristic curves for explaining a second embodiment of the amplitude compression / expansion circuit according to the present invention, FIG. 13 is a characteristic curve for explaining problems of the prior art, FIG. And FIG. 15 is a block diagram showing an amplitude compression / expansion circuit. 1, 20 ... amplitude compression / expansion circuit, 3, 22 ... multiplier circuit, 4
…… Control signal creation circuit, 23 …… Filter circuit,
24 ... amplifier circuit, 26 ... signal processing circuit.

Claims (3)

(57) [Claims] An amplitude compression / expansion input signal is provided with a first or second gain to obtain a first output signal, and a signal level of the amplitude compression / expansion input signal or the first output signal is broken. By switching the gain to be applied to the amplitude compression / expansion input signal from the first gain to the second gain when the signal level at the point is reached, the first output signal is changed in amplitude before and after the break point. First amplitude modulating means for outputting while switching a compression ratio; first subtracting means for obtaining a difference signal between the amplitude compression / expansion input signal of the first amplitude modulating means and the first output signal; The third or fourth gain is applied to the difference signal to
, And simultaneously with the switching of the gain of the first amplitude modulation means, the gain applied to the difference signal is switched from the third gain to the fourth gain to output the second output signal. Signal processing means having second amplitude modulation means for outputting a third output signal based on the second output signal; and the first output signal and the signal processing of the first amplitude modulation means Means for outputting a subtraction output of the third output signal of the means as a fourth output signal, wherein the fourth output signal of the second subtraction means is supplied to the amplitude compression / expansion input signal. Characterized in that the signal level is transmitted as an amplitude compression / expansion output signal having an amplitude compression / expansion characteristic such that the signal level smoothly transitions from the expansion characteristic to the compression characteristic at the break point as the signal level of the signal increases. Compression / expansion circuit. 2. The amplitude compression / decompression by applying a predetermined fixed gain to the second output signal of the second amplitude modulation means and outputting the second output signal as the third output signal. 2. The amplitude compression / expansion circuit according to claim 1, further comprising amplification means for giving a predetermined amplitude compression / expansion characteristic to the output signal. 3. The signal processing means outputs the second output signal of the second amplitude modulating means as the third output signal through a filter means, so that the amplitude compression / expansion output signal is output. 2. The amplitude compression / expansion circuit according to claim 1, further comprising a filter means for giving a predetermined frequency characteristic.