JP6263394B2 - FM receiver and signal correction method - Google Patents

Description

  The present invention relates to an FM receiver, a signal correction method, a signal correction program, and a recording medium on which the signal correction program is recorded.

  Conventionally, a receiving device that receives and processes broadcast waves such as FM broadcasts and reproduces sound is mounted on a moving body such as a vehicle. In such a receiving apparatus, due to the movement of the moving body, the reception situation such as the received electric field strength in the frequency band of the desired broadcast wave and the amount of noise mixed in the detection result changes. For this reason, automatic reception control (ARC) that changes the mode of signal processing for improving the S / N ratio at the time of audio output in response to a change in the reception status of a desired broadcast wave for a receiving device mounted on a mobile body. ) Has been proposed (see Patent Document 1: hereinafter referred to as “Conventional Example 1”). In the technology of Conventional Example 1, FM stereo broadcast waves are received, and mute control, so-called high cut control and stereo separation control are performed as the automatic reception control (ARC).

  In FM stereo broadcasting, a main signal (sum signal) (L + R) and a sub signal (difference signal) (LR) are transmitted by dividing the frequency band. Here, “L” is a left channel component, and “R” is a right channel component. In such FM stereo broadcasting, the SN ratio of the sub component (LR) is deteriorated by 20 dB or more compared to the main component (L + R). For this reason, the technique for improving the whole S / N ratio by improving the S / N ratio of the subcomponent (LR) has been proposed (see Patent Document 2: hereinafter referred to as “Conventional Example 2”). In the technique of Conventional Example 2, filtering control (so-called stereo emphasis control) is performed in which the frequency component in the sub signal is allowed to pass only in the band where the frequency component of the main signal (L + R) exists.

JP 2012-178804 A Japanese Patent No. 3370716

  In the technique of Conventional Example 1 described above, for example, when high cut control is performed, the SN ratio of the sub signal (LR) is improved, but a part of the sub signal (LR) is lost. For this reason, even if the stereo separation is performed based on the sub-signal after the high cut and the main signal (L + R) to generate the left channel signal and the right channel signal, the sense of stereo is reduced.

  In the technique of Conventional Example 1, for example, when stereo separation control is performed, a signal obtained by multiplying the sub-signal (LR) by a stereo separation coefficient of less than 1 (that is, according to the separation coefficient in the entire frequency band). The left channel signal and the right channel signal are generated based on the main signal (L + R) and the main signal (L + R). For this reason, the stereo feeling is reduced.

  With the technique of Conventional Example 2 described above, it is possible to reproduce the stereo feeling intended at the time of transmission from a broadcast station while improving the overall SN ratio. However, unlike the technique of Conventional Example 1, the signal processing mode cannot be changed in response to the change in the reception quality of the FM stereo broadcast wave.

  Therefore, it is conceivable to apply the technique of Conventional Example 2 after generating the sum signal and difference signal of the left channel signal and the right channel signal obtained by applying the technique of Conventional Example 1. However, some of the sub-signals lost as a result of executing the high cut control and the stereo separation control in the case where the technology of the conventional example 1 is applied are not compensated by the application of the technology of the conventional example 2. Therefore, also in this case, the stereo feeling is lowered.

  For this reason, there is a demand for a technique that can suppress a reduction in stereo feeling while appropriately changing a signal processing mode in response to a change in reception quality of FM stereo broadcast waves. Meeting this requirement is one of the problems to be solved by the present invention.

According to the first aspect of the present invention, the sum signal obtained from the left and right audio signals after control corresponding to the reception quality of the FM broadcast wave is divided into frequency bands, and the first coefficient is calculated for each divided band according to the signal level. A first coefficient calculator that calculates a second coefficient according to a noise level ratio obtained from a Fourier transform result of both the difference signal obtained from the left and right audio signals and the sum signal ; A matrix unit that calculates a left and right output audio signal from the processed difference signal obtained by filtering the difference signal based on the first coefficient and the sum signal and the sum signal ; is there.

The invention according to claim 5 is a signal correction method used in an FM receiver including a first coefficient calculation unit; a second coefficient calculation unit; and a matrix unit , wherein the first coefficient calculation unit is A first coefficient calculation unit step of dividing the sum signal obtained from the left and right audio signals after control corresponding to the reception quality of the FM broadcast wave, and calculating a first coefficient according to the signal level for each divided band ; A second coefficient calculation step in which the second coefficient calculation unit calculates a second coefficient according to a noise level ratio obtained from a Fourier transform result of both the difference signal obtained from the left and right audio signals and the sum signal ; ; wherein the matrix part is the result of the difference signal to filtering processing based on the first coefficient, the processing difference signal multiplied by said second coefficient and the sum signal and a matrix calculation step of calculating the left and right output audio signal; Signal correction with Is the method.

A sixth aspect of the present invention is a signal correction program that causes a computer included in the FM receiver to execute the signal correction method according to the fifth aspect.

The invention according to claim 7 is a recording medium on which the signal correction program according to claim 6 is recorded so as to be readable by a computer included in the FM receiver .

It is a block diagram which shows roughly the structure of the FM receiver which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the signal generation unit before correction | amendment of FIG. It is a block diagram which shows the structure of the stereo emphasis correction unit of FIG. It is a figure which shows the example of the 1st coefficient calculated by the 1st coefficient calculation part of FIG. It is a figure which shows the example of the relationship between the 2nd coefficient calculated by the 2nd coefficient calculation part of FIG. 3, and noise level ratio. It is a figure for demonstrating the correction | amendment operation | movement in the stereo emphasis correction unit of FIG. It is a block diagram which shows the structure of the stereo emphasis correction unit in the FM receiver which concerns on 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

[First Embodiment]
First, a first embodiment of the present invention will be described with reference to FIGS.

<Configuration>
FIG. 1 is a block diagram showing a schematic configuration of an FM receiver 100A according to the first embodiment of the present invention. As shown in FIG. 1, the FM receiver 100 </ b> A includes an antenna 110, an RF processing unit 120, and a detection unit 130. Further, the FM receiver 100A includes a pre-correction signal generation unit 140 and a stereo enhancement correction unit 150A. Further, the FM receiver 100A includes an analog processing unit 170, speaker units 180 _L and 180 _R , an input unit 185, and a control unit 190.

  The antenna 110 receives a broadcast wave. The reception result by the antenna 110 is sent to the RF processing unit 120 as a signal RFS.

  The RF processing unit 120 performs channel selection processing for extracting a signal of a desired station to be selected from the signal RFS in accordance with the channel selection command CSL sent from the control unit 190, and has a component in a predetermined intermediate frequency band. The intermediate frequency signal IFD is sent to the detection unit 130 and the pre-correction signal generation unit 140. The RF processing unit 120 includes an input filter, a high-frequency amplifier (RF-AMP: Radio Frequency-Amplifier), and a band-pass filter (hereinafter also referred to as “RF filter”). The RF processing unit 120 includes a mixer (mixer), an intermediate frequency filter (hereinafter also referred to as “IF filter”), an AD (Analogue to Digital) converter, and a local oscillation circuit (OSC). Yes.

  Here, the input filter is a high-pass filter that blocks a low-frequency component of the signal RFS transmitted from the antenna 110. The high frequency amplifier amplifies the signal that has passed through the input filter. The RF filter selectively passes a signal in a high frequency band among signals output from the high frequency amplifier. The mixer mixes the signal that has passed through the RF filter and the local oscillation signal supplied from the local oscillation circuit.

  The IF filter selects and passes a signal in a predetermined intermediate frequency range among the signals output from the mixer. The AD converter converts the signal that has passed through the IF filter into a digital signal. This conversion result is sent to the detection unit 130 and the pre-correction signal generation unit 140 as an intermediate frequency signal IFD.

  Note that the local oscillation circuit includes an oscillator that can control the oscillation frequency by voltage control or the like. This local oscillation circuit generates a local oscillation signal having a frequency corresponding to a desired station to be selected in accordance with a channel selection command CSL sent from the control unit 190, and supplies it to the mixer.

  The detection unit 130 receives the intermediate frequency signal IFD sent from the RF processing unit 120. The detection unit 130 performs detection processing on the intermediate frequency signal IFD, and the detection result (the component of the main signal (L + R) and the component of the sub signal (LR) are included in different frequency bands. Stereo composite signal; where the main signal (L + R) component is a signal component of the audio frequency band) is sent to the pre-correction signal generation unit 140 as the detection signal DTD.

The pre-correction signal generation unit 140 receives the detection signal DTD sent from the detection unit 130 and the intermediate frequency signal IFD sent from the RF processing unit 120. Then, the pre-correction signal generation unit 140 performs signal processing corresponding to the reception quality of the broadcast wave on the detection signal DTD, and the pre-correction left channel audio signal PAD _L and the pre-correction right signal to be subjected to stereo enhancement correction. A channel audio signal PAD _R is generated. The pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R generated in this way are sent to the stereo enhancement correction unit 150A.

  Details of the configuration of the pre-correction signal generation unit 140 will be described later.

The stereo enhancement correction unit 150A receives the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R sent from the pre-correction signal generation unit 140. Then, the stereo enhancement correction unit 150A performs the left stereo enhancement signal (left channel audio signal) AOD _L and the right stereo enhancement signal (right channel) based on the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R. Audio signal) AOD _R is calculated.

  Details of the configuration of the stereo enhancement correction unit 150A will be described later.

The analog processing unit 170 receives the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R sent from the stereo enhancement correction unit 150A. The analog processing unit 170 generates output audio signals AOS _L and AOS _R under the control of the control unit 190, and outputs the generated output audio signals AOS _L and AOS _R to the speaker units 180 _L and 180 _R. send.

The analog processing unit 170 having such a function includes a DA (Digital to Analogue) converter, a volume controller, and a power amplifier. Here, the DA converter receives the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R sent from the stereo enhancement correction unit 150A. The DA converter converts the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R into analog signals. The DA conversion unit includes two DA (Digital to Analogue) converters configured in the same manner, corresponding to the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R. The analog conversion result by the DA conversion unit is sent to the volume adjustment unit.

The volume adjustment unit receives the analog conversion result signal of the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R sent from the DA conversion unit. Then, the volume adjustment unit performs volume adjustment processing on the analog conversion result signal corresponding to each of the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R according to the volume adjustment command VLC from the control unit 190. In the first embodiment, the volume adjusting unit is configured to include two electronic volume elements and the like that are configured similarly to each other, corresponding to the two analog conversion result signals. The signal of the volume adjustment result by the volume adjustment unit is sent to the power amplification unit.

The power amplification unit receives two volume adjustment result signals sent from the volume adjustment unit. The power amplification unit power-amplifies the signal of the volume adjustment result. The power amplifying unit includes two power amplifiers configured similarly to each other, corresponding to the two sound volume adjustment results. Output audio signals AOS _L and AOS _R which are amplification results by the power amplifier are sent to the speaker units 180 _L and 180 _R.

The above speaker unit 180 _L is provided with a speaker. The speaker unit 180 _L reproduces and outputs audio in accordance with the output audio signal AOS _L sent from the analog processing unit 170.

The above speaker unit 180 _R is equipped with a speaker. The speaker unit 180 _R reproduces and outputs sound in accordance with the output sound signal AOS _R sent from the analog processing unit 170.

  The input unit 185 is configured by a key unit provided in the main body of the FM receiver 100A or a remote input device including the key unit. Here, as a key part provided in the main body, a touch panel provided in a display unit (not shown) can be used. Moreover, it can replace with the structure which has a key part, and the structure which inputs voice can also be employ | adopted. An input result to the input unit 185 is sent to the control unit 190 as input data IPD.

  The control unit 190 receives the input data IPD sent from the input unit 185. If the content of the input data IPD is channel selection, the control unit 190 generates a channel selection command CSL corresponding to the specified desired station and sends it to the RF processing unit 120. If the content of the input data IPD is volume adjustment designation, the control unit 190 generates a volume adjustment command VLC corresponding to the designated volume adjustment designation and sends it to the analog processing unit 170.

<< Configuration of Uncorrected Signal Generation Unit 140 >>
Next, the configuration of the pre-correction signal generation unit 140 will be described.

  As shown in FIG. 2, the pre-correction signal generation unit 140 includes a noise estimation unit 141 and a level detection unit 142. The pre-correction signal generation unit 140 includes a signal processing unit 143 and a stereo demodulation unit 145.

  The noise estimation unit 141 receives the detection signal DTD sent from the detection unit 130. And the noise estimation part 141 estimates the level of the in-band noise component contained in the frequency band of the signal component corresponding to the audio | voice in the detection signal DTD based on the Fourier-transform result of the detection signal DTD. The estimation result by the noise estimation unit 141 is sent to the signal processing unit 143 as an in-band noise level DND.

  In the first embodiment, the noise estimation unit 141 estimates the in-band noise level DND using, for example, the noise estimation method described in Japanese Patent Laid-Open No. 2012-178804 cited as Conventional Example 1.

  The level detection unit 142 receives the intermediate frequency signal IFD sent from the RF processing unit 120. Then, the level detector 142 detects the level of the intermediate frequency signal IFD. The detection result by the level detection unit 142 is sent to the signal processing unit 143 as the electric field intensity level ELD.

  The signal processing unit 143 receives the detection signal DTD sent from the detection unit 130, the in-band noise level DND sent from the noise estimation unit 141, and the electric field intensity level ELD sent from the level detection unit 142. Then, the signal processing unit 143 performs a mute control process and a high cut control process on the detection signal DTD with control amounts corresponding to the in-band noise level DND and the electric field strength level ELD. Further, the signal processing unit 143 calculates a stereo separation coefficient α (0 ≦ α ≦ 1) based on the in-band noise level DND and the electric field strength level ELD.

  The signal processed by the processing by the signal processing unit 143 is sent to the stereo demodulation unit 145 as a processed signal MDD. Further, the stereo separation coefficient α calculated by the signal processing unit 143 is also sent to the stereo demodulation unit 145.

Here, the signal processing unit 143 performs mute control when the in-band noise level DND is equal to or higher than the predetermined value DND _TM or the electric field intensity level ELD is equal to or lower than the predetermined value ELD _TM . In such mute control, the signal processing unit 143 increases the mute degree as the in-band noise level DND increases and as the electric field strength level ELD decreases.

The signal processing unit 143 performs high cut control when the in-band noise level DND is equal to or higher than the predetermined value DND _TH or the electric field intensity level ELD is equal to or lower than the predetermined value ELD _TH . In such high cut control, the signal processing unit 143 expands the frequency range to be high cut as the in-band noise level DND increases and as the electric field strength level ELD decreases.

In calculating the stereo separation coefficient α, the signal processing unit 143 calculates the stereo separation coefficient α when the in-band noise level DND is less than the predetermined value DND _TS or the electric field intensity level ELD is larger than the predetermined value ELD _TS. 1 ”. When the in-band noise level DND is equal to or higher than the predetermined value DND _TS or the electric field strength level ELD is equal to or lower than the predetermined value ELD _TS , the signal processing unit 143 sets the stereo separation coefficient α to “1” or lower. When the stereo separation coefficient α of “1” or less is thus calculated, the signal processing unit 143 reduces the stereo separation coefficient α as the in-band noise level DND increases and the field strength level ELD decreases. Calculation is performed.

The predetermined values DND _TM , DND _TH , and DND _TS related to the in-band noise level DND have a relationship of predetermined value DND _TM > predetermined value DND _TH > predetermined value DND _TS . The predetermined value ELD _TM relates to a field intensity level ELD, ELD _TH, with respect to the ELD _TS, and has a relation of a predetermined value ELD _TM <predetermined value ELD _TH <a predetermined value ELD _TS. In the first embodiment, at least in a state where mute control is performed, the signal processing unit 143 calculates “0” as the stereo separation coefficient α.

  The stereo demodulator 145 receives the processed signal MDD sent from the signal processor 143. Then, the stereo demodulator 145 performs stereo demodulation processing on the processed signal MDD.

  In the stereo demodulation process, the stereo demodulation unit 145 first separates a frequency component corresponding to the main signal (L + R) in the processed signal MDD and a frequency component corresponding to the sub signal (LR) in the processed signal MDD. After that, the frequency component corresponding to the sub-signal (LR) is frequency-converted into an audio band signal. The frequency component corresponding to the main signal (L + R) is an audio band signal as described above.

  Here, in a state where the mute control process is not performed in the signal processing unit 143, the frequency component corresponding to the main signal (L + R) in the processed signal MDD matches the main signal (L + R) included in the detection signal DTD. ing. In a state where the high cut control process is not performed in the signal processing unit 143, the frequency component corresponding to the frequency-converted sub signal (LR) is included in the detection signal DTD in the frequency-converted state. It corresponds to the signal (LR).

  When the mute control process is not performed in the signal processing unit 143 and the high cut control process is performed, the frequency-converted sub signal is a high frequency of the sub signal (LR) when transmitted from the broadcasting station. A part of the part is lost. In the state where the mute control process is performed in the signal processing unit 143, the frequency component corresponding to the main signal (L + R) in the processed signal MDD is uniform throughout the main signal (L + R) when transmitted from the broadcasting station. It has been attenuated. Further, in a state where the mute control process is performed in the signal processing unit 143, the frequency component corresponding to the frequency-converted sub signal (LR) is the sub signal (LR) when transmitted from the broadcasting station. A part of the high-frequency portion that has been partially lost is uniformly attenuated at the same attenuation rate as that of the frequency component corresponding to the main signal (L + R) described above.

Based on the above, in the following, the frequency component corresponding to the main signal (L + R) in the processed signal MDD is referred to as “main signal (L + R) ^* ”, and the sub-frequency converted by the stereo demodulator 145 described above. The frequency component corresponding to the signal (LR) is referred to as “sub signal (LR) ^* ”.

Subsequently, the stereo demodulation unit 145 calculates the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _{R according} to the following equations (1) and (2).
PAD _L = ((L + R) ^* + α · (LR) ^* ) / 2 (1)
PAD _R = ((L + R) ^{* −} α · (L−R) ^* ) / 2 (2)

The pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R calculated in this way are sent to the stereo enhancement correction unit 150A.

When the stereo separation control is not performed and the stereo separation coefficient α is “1”, the high cut control and the mute control are not performed, and thus the main signal (L + R) ^* and the sub signal (LR) ^. ) ^* Is a main signal (L + R) and a sub signal (LR). Therefore, when the stereo separation coefficient α is “1”, the uncorrected left channel audio signal PAD _L becomes the left channel signal L, and the uncorrected right channel audio signal PAD _R becomes the right channel signal R. . When the stereo separation coefficient α is “0”, the uncorrected left channel audio signal PAD _L and the uncorrected right channel audio signal PAD _{R become} the main signal (L + R) ^* .

<< Configuration of Stereo Enhancement Correction Unit 150A >>
Next, the configuration of the stereo enhancement correction unit 150A will be described.

As shown in FIG. 3, the stereo enhancement correction unit 150A includes a matrix unit 151, fast Fourier transform (FFT) units 152 _M and 152 _S, and a first coefficient calculation unit 153A. Further, the stereo enhancement correction unit 150A includes a second coefficient calculation unit 154, a difference signal processing unit 155A, and a matrix unit 159.

The matrix unit 151 receives the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R sent from the pre-correction signal generation unit 140. Then, the matrix unit 151 calculates the sum signal MTD and the difference signal STD by the following equations (3) and (4).
MTD = PAD _L + PAD _R = (L + R) ^* (3)
STD = PAD _L −PAD _R = α · (L−R) ^* (4)

Here, the sum signal MTD is the main signal (L + R) ^* , but the difference signal STD is the sub-signal (LR) ^* multiplied by the stereo separation coefficient α. For this reason, when stereo separation control is performed and the stereo separation coefficient α is less than “1”, the difference signal STD is obtained by attenuating the sub-signal (LR) ^* . The signal pair [MTD, STD] is different from the signal pair [(L + R) ^* , (LR) ^* ] which is a processing result by the signal processing unit 143.

  When the stereo separation coefficient α is “0”, the difference signal STD is a “0” level signal.

The sum signal MTD thus calculated is sent to the FFT unit 152 _M , the first coefficient calculation unit 153A, and the matrix unit 159. Further, the calculated difference signal STD is sent to the FFT unit 152 _S and the difference signal processing unit 155A.

The FFT unit 152 _M receives the sum signal MTD sent from the matrix unit 151. Then, the FFT unit 152 _M performs a Fourier transform on the sum signal MTD. The result (spectrum) of the Fourier transform is sent to the second coefficient calculation unit 154 as the Fourier transform result MFD.

The FFT unit 152 _S receives the difference signal STD sent from the matrix unit 151. Then, the FFT unit 152 _S performs a Fourier transform on the difference signal STD. The result (spectrum) of the Fourier transform is sent to the second coefficient calculation unit 154 as the Fourier transform result SFD.

The first coefficient calculation unit 153A includes N (N ≧ 2) band pass filters (BPF). Here, the j (= 1, 2,..., N) th BPF passes the signal components in the individual frequency range (f _{j-1 to} f _j ). In the first embodiment, the frequency range (f _{0 to} f _N ) is an audio frequency range.

The first coefficient calculation unit 153A receives the sum signal MTD sent from the matrix unit 151. In the first coefficient calculation unit 153A, each of the N BPFs extracts the signal component of the sum signal MTD in the corresponding individual frequency range. Then, the first coefficient calculation unit 153A calculates the first coefficient CA _j corresponding to each of the individual frequency ranges (f _{j−1 to} f _j ) based on the respective levels of the extracted signal components. In the first embodiment, the frequency f ₀ is 0 [Hz].

When calculating the according first coefficient, the first coefficient calculating unit 153A, when the level of the signal passing through the BPF is less than the predetermined value L _TH, the first coefficient corresponding to the individual frequency range of the signal to which the BPF is to pass Is “0”. Further, in the first coefficient calculation unit 153A, when the level of the signal that has passed through the BPF is equal to or higher than the predetermined value L _TH , the first coefficient corresponding to the individual frequency range of the signal that the BPF passes is set to “1”. .

Note that the “predetermined value L _TH ” is based on experiments, simulations, and experiences from the viewpoint of determining whether or not it is considered that the majority includes effective components that cannot be said to be noise components. Etc., based on the above.

That is, the first coefficient calculation unit 153A divides the sum signal MTD into a plurality of frequency bands, and calculates the first coefficient for each of the plurality of frequency bands based on the level of the component of the sum signal for each of the plurality of frequency bands. calculate. First coefficient calculated in this way, as the first coefficient CA ₁ to CA _N, is sent to the differential signal processing unit 155A.

The second coefficient calculation unit 154 receives the Fourier transform result MFD sent from the FFT unit 152 _M and the Fourier transform result SFD sent from the FFT unit 152 _S. Subsequently, the second coefficient calculation unit 154 estimates the noise level N _M in the sum signal MTD based on the Fourier transform result MFD. The second coefficient calculating unit 154, based on the Fourier transform result SFD, estimates the noise level N _S in the difference signal STD.

Note that, when estimating these noise levels N _M and N _S , the second coefficient calculation unit 154 uses the same method as in the case of the noise estimation unit 141 described above.

Next, the second coefficient calculation unit 154 calculates the noise level ratio R (= N _S / N _M ). Then, the second coefficient calculation unit 154 calculates the second coefficient β based on the noise level ratio R. The second coefficient β calculated in this way is sent to the difference signal processing unit 155A.

In the first embodiment, when the noise level ratio R is greater than the predetermined value R _S , the second coefficient β is “1”, and when the noise level ratio R is equal to or less than the predetermined value R _S , The two coefficients β increase as the noise level ratio R decreases. Here, the “predetermined value R _S ” is determined in advance based on a general value of the ratio between the noise level in the main signal (L + R) and the noise level in the sub signal (LR).

When the noise level ratio R is larger than the predetermined value R _S, it is estimated that the reception quality is good, the stereo separation coefficient α is “1”, and the high cut control is not performed. Further, when the noise level ratio R is equal to or less than the predetermined value R _S , the reception quality becomes worse as the noise level ratio R becomes smaller, the stereo separation coefficient α becomes smaller, or the high cut amount by the high cut control becomes larger. It is estimated that For this reason, in the first embodiment, based on the noise level ratio R, the degree of reduction from the sub-signal (LR) of the difference signal STD due to the stereo separation coefficient α or the high cut control is reasonably estimated. It has become.

The difference signal processing unit 155A includes N (N ≧ 2) variable BPFs, an addition unit that adds output signals from each variable BPF, and an amplification unit that amplifies the addition result by the addition unit. Has been. Here, the j (= 1, 2,..., N) -th variable BPF is a signal component in the individual frequency range (f _{j−1 to} f _j ) similar to that of the BPF in the first coefficient calculation unit 153A described above. _Are passed at a passage rate corresponding to the first coefficient CA _j . The amplifying unit performs signal amplification at an amplification factor corresponding to the second coefficient β.

The difference signal processing unit 155A configured as described above includes the difference signal STD sent from the matrix unit 151, the first coefficients CA _{1 to} CA _N sent from the first coefficient calculation unit 153A, and the second coefficients. The second coefficient β sent from the calculation unit 154 is received. Then, the difference signal processing section 155A, based on the first coefficient CA ₁ to CA _N and the second coefficient beta, processing the difference signal STD.

In processing the difference signal, in the difference signal processing unit 155A, first, each of the N variable BPFs uses the signal component of the difference signal STD in the corresponding individual frequency range as the first coefficient corresponding to the individual frequency range. In the case of “1”, it is passed as it is, and when the first coefficient is “0”, it is blocked. As a result, only the signal component of the difference signal STD in the individual frequency range in which an effective audio signal component exists in the sum signal MTD (that is, the level of the signal component is equal to or higher than the predetermined value _LTH ) is selected. For this reason, by processing the difference signal STD based on the first coefficients CA _{1 to} CA _N , a component that is considered to have a small contribution to the stereo feeling and include a lot of noise components in the difference signal STD is removed.

  Subsequently, in the difference signal processing unit 155A, the adding unit adds the output signals for each variable BPF. Hereinafter, the signal resulting from the addition by the adding unit is referred to as “signal ADD”.

In the difference signal processing unit 155A, the amplifying unit performs amplification on the signal ADD according to the following equation (5) to generate a processed difference signal SAD.
SAD = β · ADD (5)
The machining difference signal SAD generated in this way is sent to the matrix unit 159.

  When the stereo separation coefficient α is “0”, the difference signal STD is a “0” level signal, so that the signal ADD and the processed difference signal SAD are also “0” level signals.

  Here, if the stereo separation coefficient α is greater than “0” and less than “1”, the processed difference signal SAD is an individual frequency range in which an effective audio signal component exists in the sum signal MTD. The signal component of the difference signal STD in FIG. 4 is a signal whose level of reduction from the sub-signal (LR) of the difference signal STD due to the stereo separation coefficient α or the high cut control is alleviated.

The matrix unit 159 receives the sum signal MTD sent from the matrix unit 151 and the processed difference signal SAD sent from the difference signal processing unit 155A. Then, the matrix unit 159 calculates the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R by the following equations (6) and (7).
AOD _L = (MTD + SAD) / 2 (6)
AOD _R = (MTD−SAD) / 2 (7)
The left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R thus calculated are sent to the analog processing unit 170.

Incidentally, in FIG. 4 shows an example of the first coefficient CA ₁ to CA _N which is calculated as described above in the first coefficient calculating unit 153A are shown. FIG. 5 shows an example of change of the second coefficient β according to the change of the noise level ratio R.

<Operation>
Next, the operation of the FM receiver 100A configured as described above will be described mainly focusing on the stereo enhancement correction processing in the stereo enhancement correction unit 150A.

  As a premise, it is assumed that a channel selection designation has already been input by the user to the input unit 185, and a channel selection command CSL corresponding to the designated desired station has been sent to the RF processing unit 120. Further, it is assumed that a volume adjustment designation has already been input by the user to the input unit 185, and a volume adjustment command VLC corresponding to the designated volume adjustment mode has been sent to the analog processing unit 170 (FIG. 1). reference).

  When a broadcast wave is received by the antenna 110 in such a state, a signal RFS is sent from the antenna 110 to the RF processing unit 120. Then, in the RF processing unit 120, after the signal of the desired station to be selected is converted into a signal in the intermediate frequency band, AD conversion is performed. The RF processing unit 120 sends the AD conversion result to the detection unit 130 and the pre-correction signal generation unit 140 as an intermediate frequency signal IFD (see FIG. 1).

  Upon receiving the intermediate frequency signal IFD, the detection unit 130 performs detection processing on the intermediate frequency signal IFD. Then, the detection unit 130 sends the detection result (stereo composite signal) to the pre-correction signal generation unit 140 as a detection signal DTD (see FIG. 1).

  When receiving the intermediate frequency signal IFD, in the pre-correction signal generation unit 140, the level detection unit 142 detects the level of the intermediate frequency signal IFD. Then, the level detection unit 142 sends the detection result to the signal processing unit 143 as the electric field intensity level ELD (see FIG. 2).

  In addition, when receiving the detection signal DTD, in the pre-correction signal generation unit 140, the noise estimation unit 141 is included in the frequency band of the signal component corresponding to the sound in the detection signal DTD based on the Fourier transform result of the detection signal DTD. Estimate the level of the in-band noise component. And the noise estimation part 141 sends an estimation result to the signal processing part 143 as an in-band noise level DND (refer FIG. 2).

  Upon receiving the electric field strength level ELD and the in-band noise level DND, the signal processing unit 143 controls the detection signal DTD with the control amount corresponding to the in-band noise level DND and the electric field strength level ELD, and mute control processing and high cut control. Processing is performed to generate a processed signal MDD, and a stereo separation coefficient α (0 ≦ α ≦ 1) is calculated based on the in-band noise level DND and the electric field strength level ELD. Then, the signal processing unit 143 sends the processed signal MDD and the stereo separation coefficient α to the stereo demodulation unit 145 (see FIG. 2).

Upon receiving the processed signal MDD and the stereo separation coefficient α, the stereo demodulation unit 145 uses the stereo separation coefficient α to generate the uncorrected left channel audio signal PAD _L and the uncorrected right channel audio signal PAD _R as described above (1 ) And (2). Then, the stereo demodulator 145 sends the uncorrected left channel audio signal PAD _L and the uncorrected right channel audio signal PAD _R to the stereo enhancement correction unit 150A (see FIG. 2).

When the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R are received, the stereo enhancement correction unit 150A performs stereo enhancement correction processing.

<< Sum signal and difference signal calculation process >>
In such stereo enhancement correction processing, in the stereo enhancement correction unit 150A, first, the matrix unit 151 performs the above-described equations (3) and (3) based on the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R. 4) The sum signal MTD and the difference signal STD are calculated by the equation (4). The matrix unit 151 sends the sum signal MTD to the FFT unit 152 _M , the first coefficient calculation unit 153A, and the matrix unit 159, and sends the difference signal STD to the FFT unit 152 _S and the difference signal processing unit 155A (FIG. 3).

  An example of the spectrum of the difference signal STD calculated in this way is shown in FIG. FIG. 6A shows an example of the spectrum of the sub-signal (LR) for comparison with the example of the spectrum of the difference signal STD shown in FIG. 6B. .

Here, in the spectrum of the difference signal STD shown in FIG. 6B, only the stereo separation control is performed in the signal processing unit 143, the stereo separation coefficient α is larger than “0”, and “1”. This is an example of the case of less than. In this example, the spectrum of the sub signal (LR) (= (LR) ^* ) shown in FIG. 6A is compared with the spectrum of the difference signal STD shown in FIG. As a result, due to the contribution of the stereo separation coefficient α, the spectrum of the difference signal STD is an attenuation of the spectrum of the sub-signal (LR).

<< Calculation processing of first coefficient >>
Upon receiving the sum signal MTD, first coefficient calculation unit 153A calculates a first coefficient CA ₁ to CA _N.

When calculating the according first coefficient CA ₁ to CA _N, the first coefficient calculating unit 153A, first, each of the N BPF extracts the signal components of the sum signal MTD of the corresponding individual frequency range. Subsequently, the first coefficient calculating unit 153A, when the level of the signal passing through the BPF is less than the predetermined value L _TH, the first coefficient corresponding to the frequency range of the signal to which the BPF is to pass the "0". Further, the first coefficient calculating unit 153A, when the level of the signal passing through the BPF is equal to or greater than the predetermined value L _TH, the first coefficient corresponding to the frequency range of the signal to which the BPF is to pass the "1". The first coefficient calculating unit 153A has a first coefficient CA ₁ to CA _N, and sends the difference signal processing section 155A (see FIG. 3).

<< Calculation processing of second coefficient >>
In calculating the second coefficient, first, the FFT unit 152 _M that has received the sum signal MTD performs Fourier transform on the sum signal MTD, and sends the Fourier transform result MFD to the second coefficient calculation unit 154. In addition, the FFT unit 152 _S that has received the difference signal STD performs a Fourier transform on the difference signal STD, and sends the Fourier transform result SFD to the second coefficient calculation unit 154 (see FIG. 3).

Fourier transform result MFD, receives the SFD, second coefficient calculating unit 154, the Fourier transform results based on MFD, with estimates the noise level N _M in the sum signal MTD, based on the Fourier transform result SFD, the difference signal STD estimating the noise level N _S in. Subsequently, the second coefficient calculation unit 154 calculates the noise level ratio R (= N _S / N _M ). Then, the second coefficient calculation unit 154 calculates the second coefficient β based on the noise level ratio R, and sends the calculated second coefficient β to the difference signal processing unit 155A (see FIG. 3).

《Difference signal processing》
The difference signal processing unit 155A receives the difference signal STD sent from the matrix unit 151, the first coefficients CA _{1 to} CA _N sent from the first coefficient calculation unit 153A, and the first coefficients sent from the second coefficient calculation unit 154. Receives 2 coefficients β. Then, the difference signal processing section 155A, based on the first coefficient CA ₁ to CA _N and the second coefficient beta, processing the difference signal STD.

  When processing the difference signal STD, first, in the difference signal processing unit 155A, each of the N variable BPFs converts the signal component of the difference signal STD in the corresponding individual frequency range into the first coefficient corresponding to the individual frequency range. When “1” is “1”, it is passed as it is, and when the first coefficient is “0”, it is blocked. As a result, only the signal component of the difference signal STD in the individual frequency range where an effective audio signal component exists in the sum signal MTD is selected. Subsequently, in the difference signal processing unit 155A, the addition unit adds the output signals for each variable BPF and calculates the above-described signal ADD.

An example of the spectrum of the signal ADD calculated in this way is shown in FIG. The example shown in FIG. 6 (C), the first coefficient CA ₁ to CA _N is an example of a case was a value shown in FIG. 4 described above.

  Next, in the difference signal processing unit 155A, the amplification unit performs amplification according to the above-described equation (5) on the signal ADD to generate a processed difference signal SAD. The machining difference signal SAD generated in this way is sent to the matrix unit 159 (see FIG. 3).

An example of the spectrum of the machining difference signal SAD generated in this way is shown in FIG. As can be seen from the comparison of the spectrum of FIG. 6D and the spectrum of FIG. 6B with the spectrum of FIG. 6A, the processed difference signal SAD has an effective audio signal component in the sum signal MTD. The signal component of the difference signal STD in the individual frequency range (that is, the level of the signal component is equal to or higher than the predetermined value L _TH ) is a sub-signal (L−) of the difference signal STD caused by the stereo separation coefficient α or the high cut control. The degree of reduction from R) is moderated.

<< Calculation processing of left stereo enhancement signal and right stereo enhancement signal >>
When receiving the sum signal MTD sent from the matrix unit 151 and the processed difference signal SAD sent from the difference signal processing unit 155A, the matrix unit 159 calculates the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R. To do. When calculating the take left stereo enhancement signal AOD _L and right stereo enhancement signal AOD _R, the matrix portion 159 by the above-described (6) and (7), the left stereo enhancement signal AOD _L and right stereo enhancement signal AOD _R calculate. Then, the matrix unit 159 sends the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R to the analog processing unit 170 (see FIG. 3).

When the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R sent from the stereo enhancement correction unit 150A are received, the analog processing unit 170 sequentially performs signal processing by the DA conversion unit, the volume adjustment unit, and the power amplification unit. As a result, output audio signals AOS _L and AOS _R are generated. Then, the analog processing unit 170 sends the generated output audio signals AOS _L and AOS _R to the speaker units 180 _L and 180 _R (see FIG. 1). As a result, the speaker units 180 _L and 180 _R reproduce and output audio in accordance with the output audio signals AOS _L and AOS _R.

As described above, in the first embodiment, the signal RFS that is the reception result of the FM stereo broadcast wave by the antenna 110 is sequentially processed by the RF processing unit 120, the detection unit 130, and the pre-correction signal generation unit 140 to perform correction. A front left channel audio signal PAD _L and a pre-correction right channel audio signal PAD _R are generated. When generating the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R , the pre-correction signal generation unit 140 performs mute control on the detection signal DTD in accordance with the reception quality of the broadcast wave. Performs high-cut control and stereo separation control.

The stereo enhancement correction unit 150A that receives the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R performs stereo enhancement processing. In such stereo enhancement processing, in the stereo enhancement correction unit 150A, the matrix unit 151 adds the uncorrected left channel audio signal PAD _L and the uncorrected right channel audio signal PAD _R to the sum signal MTD and the uncorrected left channel audio. A difference signal STD obtained by subtracting the uncorrected right channel audio signal PAD _R from the signal PAD _L is calculated.

Subsequently, the first coefficient calculation unit 153A divides the sum signal MTD into a plurality of frequency bands, and, based on the level of the component of the sum signal MTD for each of the plurality of frequency bands, for each of the plurality of frequency bands, calculating the coefficients CA ₁ to CA _N. In parallel with the calculation process of the first coefficient CA ₁ to CA _N by the first coefficient calculating unit 153A, the second coefficient calculating unit 154, the noise level in the sum signal MTD based on MFD Fourier transform result of the sum signal MTD N _M estimation, and, after the estimation of the noise level N _S in the difference signal STD based on the Fourier transform SFD of the difference signal STD, based on these estimation results, calculates a second coefficient beta.

Then, the difference signal processing section 155A, based on the first coefficient CA ₁ to CA _N and the second coefficient beta, and generates a processed difference signal SAD by processing the difference signal STD. The matrix unit 159 calculates the left stereo enhancement signal AOD _L based on the addition result obtained by adding the sum signal MTD and the processed difference signal SAD, and subtracts the processed difference signal SAD from the sum signal MTD. Based on the obtained subtraction result, the right stereo enhancement signal AOD _R is calculated.

  Therefore, according to the first embodiment, it is possible to suppress a decrease in stereo feeling while appropriately changing the signal processing mode in response to a change in reception quality of FM stereo broadcast waves.

In the first embodiment, the second coefficient β increases as the noise level ratio R decreases when the noise level ratio R is equal to or smaller than the predetermined value R _S. Therefore, it is possible to generate the processed difference signal SAD that reasonably compensates for the reduction from the sub signal (LR) of the difference signal STD caused by the stereo separation coefficient α or the high cut control.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference mainly to FIG.

<Configuration>
The FM receiver according to the second embodiment includes a stereo enhancement correction unit 150B having the configuration shown in FIG. 7 instead of the stereo enhancement correction unit 150A, as compared with the FM receiver 100A according to the first embodiment described above. Only the point is different. In the following, description will be given focusing on such differences.

  In the following description, the FM receiver according to the second embodiment is referred to as “FM receiver 100B”.

As shown in FIG. 7, the stereo enhancement correction unit 150B is different from the stereo enhancement correction unit 150A (see FIG. 3) described above in (a) a first coefficient calculation unit instead of the first coefficient calculation unit 153A. 153B is provided, (b) a difference signal processing unit 155B is provided instead of the difference signal processing unit 155A, and (c) inverse Fourier transform (IFFT) units 156 _M and 156 _S are provided. .

Incidentally, the matrix portion 151 of the second embodiment, the sum signal MTD, sent to only the FFT unit 152 _M. Further, FFT section 152 _M in the second embodiment sends the Fourier transform result MFD, the first coefficient calculating unit 153B, the second coefficient calculating unit 154 and the IFFT section 156 _M.

Furthermore, the FFT unit 152 _S in the second embodiment sends the Fourier transform result SFD to the second coefficient calculation unit 154 and the difference signal processing unit 155B. In addition, the second coefficient calculation unit 154 in the second embodiment sends the second coefficient β to the difference signal processing unit 155B.

The first coefficient calculating unit 153B described above, subjected to Fourier transform result MFD sent from the FFT unit 152 _M. The first coefficient calculating unit 153B is the Fourier transform results based on MFD, to calculate a first coefficient CA ₁ to CA _N the same as in the first embodiment.

It said difference signal processing section 155B includes a Fourier transform result SFD sent from the FFT unit 152 _S, first coefficient CA ₁ to CA _N sent from the first coefficient calculating unit 153B, and the second coefficient calculating unit 154 The sent second coefficient β is received. Then, the difference signal processing section 155B, based on the first coefficient CA ₁ to CA _N and the second coefficient beta, the Fourier transform result (i.e., the spectrum of the difference signal STD) processing the SFD. This processing result is sent to the IFFT unit 156 _S as a processing difference signal spectrum SSD.

When processing the Fourier transform result SFD, the difference signal processing unit 155B sets the components in the frequency range (f _{j−1 to} f _j ) (j = 1 to N) of the Fourier transform result SFD as “SFD _j ” as follows: The processing difference signal spectrum SSD is calculated by calculating the component SSD _j in the frequency range (f _{j−1 to} f _j ) according to the equation (8).
SSD _j = CA _j · β · SFD _j (8)

The IFFT unit 156 _M receives the Fourier transform result (that is, the spectrum of the sum signal MTD) MFD sent from the FFT unit 152 _M. Then, the IFFT unit 156 _M performs inverse Fourier transform on the Fourier transform result MFD. The result of the inverse Fourier transform is a sum signal MTD. The sum signal MTD obtained by the inverse Fourier transform by the IFFT unit 156 _M is sent to the matrix unit 159.

The IFFT unit 156 _S receives the processed difference signal spectrum SSD sent from the difference signal processing unit 155B. Then, the IFFT unit 156 _S performs inverse Fourier transform on the processed difference signal spectrum SSD. The result of the inverse Fourier transform is sent to the matrix unit 159 as a processing difference signal SAD.

<Operation>
The operation of the FM receiver 100B configured as described above will be described mainly focusing on the difference from the operation of the FM receiver 100A described above.

  As a premise, it is assumed that a channel selection designation has already been input by the user to the input unit 185, and a channel selection command CSL corresponding to the designated desired station has been sent to the RF processing unit 120. Further, it is assumed that a volume adjustment designation has already been input by the user to the input unit 185, and a volume adjustment command VLC corresponding to the designated volume adjustment mode has been sent to the analog processing unit 170 (FIG. 1). reference).

When a broadcast wave is received by the antenna 110 in such a state, a signal RFS is sent from the antenna 110 to the RF processing unit 120. Similarly to the case of the first embodiment, processing by the RF processing unit 120, the detection unit 130, and the pre-correction signal generation unit 140 is sequentially performed, and the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio are processed. Signal PAD _R is generated. The pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R generated in this way are sent to the stereo enhancement correction unit 150B.

When the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R are received, the stereo enhancement correction unit 150B performs stereo enhancement correction processing.

<< Sum signal and difference signal calculation process >>
In such stereo enhancement correction processing, in the stereo enhancement correction unit 150B, first, the matrix unit 151 is based on the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _{R as} in the case of the first embodiment. Thus, the sum signal MTD and the difference signal STD are calculated. Then, the matrix unit 151 sends the sum signal MTD to the FFT unit 152 _M and sends the difference signal STD to the FFT unit 152 _S (see FIG. 7).

<< Calculation processing of first coefficient >>
Upon receiving the Fourier transform result MFD sent from the FFT unit 152 _M, first coefficient calculation unit 153B includes a Fourier transform results based on MFD, to calculate a first coefficient CA ₁ to CA _N. The first coefficient calculating unit 153B includes a first coefficient CA ₁ to CA _N, and sends the difference signal processing unit 155B (see FIG. 7).

<< Calculation processing of second coefficient >>
In parallel with the calculation of the first coefficient CA ₁ to CA _N described above, the second coefficient calculating unit 154, in the same manner as in the first embodiment, calculates a second coefficient beta. Then, the second coefficient calculation unit 154 sends the second coefficient β to the difference signal processing unit 155B (see FIG. 7).

《Difference signal processing》
The difference signal processing section 155B includes a Fourier transform result SFD sent from the FFT unit 152 _S, first coefficient CA ₁ to CA _N sent from the first coefficient calculating unit 153B, and is sent from the second coefficient calculating unit 154 The second coefficient β is received. Then, the difference signal processing section 155B, based on the first coefficient CA ₁ to CA _N and the second coefficient beta, processing the Fourier transform result SFD.

When processing the Fourier transform result SFD, the difference signal processing unit 155B calculates the component SSD _j in the frequency range (f _{j-1 to} f _j ) by the above-described equation (8), thereby processing the processed difference signal spectrum SSD. Is calculated. Then, the difference signal processing unit 155B sends the processed difference signal spectrum SSD to the IFFT unit 156 _S (see FIG. 7).

<< Calculation processing of left stereo enhancement signal and right stereo enhancement signal >>
Upon receiving the Fourier transform result MFD sent from the FFT unit 152 _M , the IFFT unit 156 _M performs inverse Fourier transform on the Fourier transform result MFD, and calculates a sum signal MTD. In addition, inverse Fourier transform is performed on the processed difference signal spectrum SSD sent from the difference signal processing unit 155B to calculate the processed difference signal SAD.

When the sum signal MTD and the processed difference signal SAD calculated in this way are received, the matrix unit 159 calculates the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R in the same manner as in the first embodiment. Then, the matrix unit 159 sends the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R to the analog processing unit 170 (see FIG. 7).

Upon receiving the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R sent from the stereo enhancement correction unit 150B, the analog processing unit 170 outputs the output audio signal AOS _{L in the same} manner as in the first embodiment. , AOS _R is generated. Then, the analog processing unit 170 sends the generated output audio signals AOS _L and AOS _R to the speaker units 180 _L and 180 _R (see FIG. 1). As a result, the speaker units 180 _L and 180 _R reproduce and output audio in accordance with the output audio signals AOS _L and AOS _R.

As described above, in the second embodiment, the signal RFS that is the reception result of the FM stereo broadcast wave by the antenna 110 is sequentially processed by the RF processing unit 120, the detection unit 130, and the pre-correction signal generation unit 140 to perform correction. A front left channel audio signal PAD _L and a pre-correction right channel audio signal PAD _R are generated. When generating the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R , the pre-correction signal generation unit 140 performs mute control on the detection signal DTD in accordance with the reception quality of the broadcast wave. Performs high-cut control and stereo separation control.

The stereo enhancement correction unit 150B that has received the pre-correction left channel audio signal PAD _L and the pre-correction right channel audio signal PAD _R performs stereo enhancement processing. In such stereo enhancement processing, in the stereo enhancement correction unit 150B, the matrix unit 151 adds the uncorrected left channel audio signal PAD _L and the uncorrected right channel audio signal PAD _{R in the same} manner as in the first embodiment. A difference signal STD obtained by subtracting the uncorrected right channel audio signal PAD _R from the signal MTD and the uncorrected left channel audio signal PAD _L is calculated.

Subsequently, the first coefficient calculating unit 153B is based on the MFD Fourier transform result of the sum signal MTD, it calculates a similar first coefficient CA ₁ to CA _N in the first embodiment. In parallel with the calculation process of the first coefficient CA ₁ to CA _N by the first coefficient calculating unit 153B, the second coefficient calculating unit 154, in the same manner as in the first embodiment, calculates a second coefficient β To do.

Then, the difference signal processing unit 155B is based on the first coefficient CA ₁ to CA _N and the second coefficient beta, and processing the Fourier transform result SFD, it generates a processed difference signal spectrum SSD. The matrix unit 159 is based on the sum signal MTD obtained by inverse Fourier transform of the Fourier transform result MFD and the processed difference signal SAD obtained by inverse Fourier transform of the processed difference signal spectrum SSD in the first embodiment. In the same manner as described above, the left stereo enhancement signal AOD _L and the right stereo enhancement signal AOD _R are calculated.

  Therefore, according to the second embodiment, as in the case of the first embodiment, the deterioration of the stereo feeling is suppressed while appropriately changing the signal processing mode corresponding to the change in the reception quality of the FM stereo broadcast wave. can do.

In the second embodiment, as in the case of the first embodiment, the second coefficient β increases as the noise level ratio R decreases when the noise level ratio R is equal to or smaller than the predetermined value R _S. It has become. Therefore, it is possible to generate the processed difference signal SAD that reasonably compensates for the reduction from the sub signal (LR) of the difference signal STD caused by the stereo separation coefficient α or the high cut control.

[Modification of Embodiment]
The present invention is not limited to the first and second embodiments described above, and various modifications are possible.

  For example, in the first and second embodiments, the change mode illustrated in FIG. 5 is illustrated as the change mode of the second coefficient according to the change in the noise level ratio when the noise level ratio is equal to or less than a predetermined value. On the other hand, when the noise level ratio is equal to or less than a predetermined value, a change mode different from the change mode shown in FIG. 5 may be adopted as a change mode in which the second coefficient increases as the noise level ratio decreases.

  Further, as a noise level estimation method, a method other than the estimation method exemplified in the first and second embodiments may be employed.

  In the first and second embodiments, the first coefficient is set to one of the value corresponding to the cutoff and the value corresponding to the passage as it is, but depending on the level of the component in the individual frequency range, The corresponding first coefficient may be changed.

  In the first embodiment, when processing the difference signal, the processing based on the second coefficient is performed on the result of processing based on the first coefficient. On the other hand, processing based on the first coefficient may be performed on the result of processing based on the second coefficient, or processing based on the first coefficient and processing based on the second coefficient may be performed simultaneously. May be.

  In the second embodiment, the sum signal MTD supplied to the matrix unit 159 is obtained by subjecting the sum signal MTD calculated by the matrix unit 151 to Fourier transform and then inverse Fourier transform. On the other hand, the sum signal MTD calculated by the matrix unit 151 may be delayed to obtain the sum signal MTD supplied to the matrix unit 159.

  The detection unit, pre-correction signal generation unit, stereo enhancement correction unit, and control unit in the first or second embodiment described above are provided with a central processing unit (CPU), a DSP (Digital Signal Processor), and the like. The computer may be configured as a computing unit, and a part of or all of the processing in the above embodiment may be executed by executing a program prepared in advance on the computer. This program is recorded on a computer-readable recording medium such as a hard disk, CD-ROM, or DVD, and is read from the recording medium and executed by the computer. The program may be acquired in a form recorded on a portable recording medium such as a CD-ROM or DVD, or may be acquired in a distribution form via a network such as the Internet. Also good.

100A, 100B ... FM receiver 140 ... Pre-correction signal generation unit (pre-correction signal generation unit)
151... Matrix part (first matrix part)
153A, 153B ... 1st coefficient calculation part 154 ... 2nd coefficient calculation part 155A, 155B ... Difference signal processing part 159 ... Matrix part (2nd matrix part)

Claims (7)

A first coefficient calculation unit that frequency-divides the sum signal obtained from the left and right audio signals after control corresponding to the reception quality of the FM broadcast wave, and calculates a first coefficient according to the signal level for each divided band ;
A second coefficient calculation unit that calculates a second coefficient according to a noise level ratio obtained from a Fourier transform result of both the difference signal obtained from the left and right audio signals and the sum signal ;
A matrix unit that calculates left and right output audio signals from the processed difference signal obtained by filtering the difference signal based on the first coefficient and the summed signal multiplied by the second coefficient ;
An FM receiver comprising:   2. The FM receiver according to claim 1, wherein the control corresponding to the reception quality is at least one of high cut control and stereo separation control for a signal after the FM broadcast wave is detected. The second coefficient increases as the division value decreases when a division value obtained by dividing the noise component level of the difference signal by the noise component level of the sum signal is equal to or less than a first predetermined value. The FM receiver according to claim 1 or 2. The first coefficient, the signal level of the divided band less than the second predetermined value is a value corresponding to the blocking of the filtering process, for the signal level is the second predetermined value or more sub-bands, the It is a value corresponding to the passage in filtering processing , The FM receiver according to any one of claims 1 to 3 characterized by things. A signal correction method used in an FM receiver comprising: a first coefficient calculation unit; a second coefficient calculation unit; and a matrix unit;
The first coefficient calculation unit divides the frequency band of the sum signal obtained from the left and right audio signals after control corresponding to the reception quality of the FM broadcast wave, and calculates the first coefficient according to the signal level for each divided band. A first coefficient calculation unit step;
A second coefficient calculating step in which the second coefficient calculating unit calculates a second coefficient in accordance with a noise level ratio obtained from a Fourier transform result of both the difference signal obtained from the left and right audio signals and the sum signal ;
Said matrix portion, the result of the difference signal to filtering processing based on the first coefficient, the processing difference signal multiplied by said second coefficient and the sum signal and a matrix calculation step of calculating the left and right output audio signal;
A signal correction method comprising:   A signal correction program causing a computer included in the FM receiver to execute the signal correction method according to claim 5.   7. A recording medium on which the signal correction program according to claim 6 is recorded so as to be readable by a computer included in the FM receiver.

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