JP4841324B2 - Surround generator - Google Patents

Description

  The present invention relates to a surround generation apparatus that generates a multi-channel surround signal from a two-channel stereo signal, and more particularly to a surround generation apparatus mounted on an in-vehicle audio apparatus.

  In order to provide a sound field with a sense of presence or a surround effect in a home theater or a car interior space, a 5ch or 5.1ch surround system in which a plurality of speakers are arranged in front of and behind a listener is widely used. In such a system, a conversion technique for generating a multi-channel surround signal from a 2-channel stereo signal is used. For example, in a passenger compartment, two-channel (Lch and Rch) stereo signals are output from the front left and right speakers, respectively, and a surround signal obtained from the difference between the stereo signals is output from the rear left and right speakers, respectively. It has come to be.

  When a surround signal is generated from a difference between two-channel stereo signals, the generated surround signals have phases opposite to each other, and there is a drawback in that the listener (listener) feels out of phase or discomfort. In order to solve this drawback, Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for decorating (or decorrelating) a two-channel stereo signal using an adaptive filter and generating a surround signal from the difference between the decorrelated signals. It is disclosed.

  In the decorrelation process, it has been understood from the viewpoint of performance and audibility that the correlation removal for the middle and high frequency components can be performed satisfactorily. Also, for 2-channel signals such as CDs, the chorus and sound effects are intentionally shifted in the process of recording and mixing to de-correlate such as reverberation in order to improve the creativity and artistry. There are many.

FIG. 1 is a diagram illustrating a configuration example of an adaptive decorrelator using an FIR filter disclosed in Patent Document 1. In FIG. The input signal X of one channel is divided by the delay processor Z ^-1 multistage, the coefficient processor W _0, W 1 to each of the _output, ... superimposes a predetermined coefficient by W _k, By adding this with an adder Σ, a decorrelation filter for extracting a signal component highly correlated with the input signal Y of the other channel from the input signal X of one channel is provided. The characteristics of the decorrelation filter include the output signal RES and the error signal e obtained from the input signal Y from the other channel, the input signal X of one channel, and a step size parameter that controls the update rate of the filter coefficient. Is provided with a coefficient update processor 5 that changes sequentially. The computing unit 4 obtains a surround signal from the difference between the output RES from the decorrelation filter and the input signal Y of the other channel.

JP 2003-333698 A

  FIG. 2 is a block diagram illustrating a configuration example of the surround generation device provided in the in-vehicle audio device. The two-channel stereo signal L / R becomes the front stereo signal FL / FR and is input to the decorrelation processing unit AST. In the stereo signal L / R, the correlation component is removed, and a surround signal SL / SR is generated from the difference.

  In the stereo signal L / R, the low frequency signal has a relatively high correlation, and when input to the decorrelation processing unit AST, the low frequency signal having a high correlation tends to be suppressed. As a result, there were some scenes where the listener (listener) demanded more bass volume when listening to music. 3A shows the relationship between the sound range of the front FL / FR and the output level, and FIG. 3B shows the relationship between the sound range of the rear channel SL / SR and the output level. In these output waveforms, comparing the ranges indicated by the low-frequency ellipses Q1 and Q2 of 150 Hz or less, it can be seen that the output level of the rear channel is about 10 dB smaller than that of the front channel.

  In general, the frequency range of 80 Hz to 200 Hz matches the lower limit of male vocals (baritone and tenor), and this range produces a sense of volume. There is a problem that there is a lack of sense of volume.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a surround generation apparatus that generates a surround signal with a large amount of feeling during multi-channel reproduction.

  A surround generation apparatus for generating a multi-channel surround signal from a 2-channel stereo signal according to the present invention receives a 2-channel stereo signal, removes a correlation component of the stereo signal, and performs a decorrelation process of the stereo signal. Correlation processing means, extraction means for extracting a signal in a predetermined frequency band from a two-channel stereo signal, and addition means for adding the extracted signal to an output signal of the decorrelation processing means and outputting a surround signal Have

  Preferably, the extraction unit extracts a low-frequency band audio signal, and a low-pass filter whose cut-off frequency is set to 200 Hz or less can be used. The adding means may include a first amplifier that adjusts the gain of the signal extracted by the extracting means and a second amplifier that adjusts the gain of the output signal of the decorrelation processing means. The surround generation apparatus further includes control means for changing the step size parameter of the adaptive digital filter included in the decorrelation processing means and changing the gains of the first and second amplifiers according to the change of the step size parameter. Have. The control means increases the gain of the first amplifier in response to an increase in the step size parameter. The surround generation apparatus may further include input means for instructing variable step size parameters.

  Preferably, the extraction unit may vary the frequency band to be extracted in response to the gain of the first amplifier of the addition unit. In this case, when the gain of the first amplifier is increased, the cutoff frequency of the low-pass filter is increased, and when the gain of the first amplifier is decreased, the cutoff frequency is varied.

  According to the present invention, a signal of a predetermined frequency band (preferably, a low frequency band of 200 Hz or less) is extracted from the two-channel stereo signal, and added to the decorrelated signal. Therefore, a surround signal with a sense of volume can be obtained during multi-channel playback.

  The best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a block diagram showing the configuration of the in-vehicle audio apparatus according to the embodiment of the present invention. The in-vehicle audio apparatus 10 reproduces an audio signal received by radio broadcast or television broadcast, or reproduces an audio signal stored in a medium such as a CD, DVD, or hard disk. Below, the example which receives FM broadcast and reproduces it is demonstrated.

  As shown in FIG. 4, the in-vehicle audio device 10 includes an antenna 20 that receives a radio broadcast, a reception module 30 that receives an RF signal received by the antenna 20, an audio signal from the reception module 30, and a surround signal. A surround generation unit 40 to be generated and a controller 50 that receives the reception sensitivity of the reception signal in the reception module 30 and controls the surround generation unit 40 are included. The surround generation unit 40 receives the two-channel stereo signal L / R and generates the surround signals SL and SR therefrom. When generating a 5-channel surround signal, a signal CT (Center) is further generated from the sum component of the stereo signals R and L.

  FIG. 5 is a diagram showing a layout of speakers in the interior space. Front speakers FL and FR are disposed on the left and right sides of the front seat, and rear speakers RL and RR are disposed on the left and right sides of the rear seat. An Lch stereo signal (hereinafter referred to as stereo signal L) is output from the front speaker FL, and an Rch stereo signal (hereinafter referred to as stereo signal R) is output from the front speaker FR. An Lch surround signal (hereinafter referred to as a surround signal SL) is output from the rear speaker RL, and an Rch surround signal (hereinafter referred to as a surround signal SR) is output from the rear speaker RR. In the case of a 5-channel surround space, a speaker CT is arranged at the center of the seat, and a signal CT is output therefrom.

  FIG. 6 is a block diagram showing a general internal configuration of a receiving module that receives FM broadcasts. The receiving module 30 receives an RF signal from the antenna 20 and amplifies the RF signal, a tuning circuit 110 that selects a frequency signal of a desired station from the amplified RF signal, and a frequency signal from the local oscillator 120. A mixer 130 for mixing an RF signal to generate an intermediate frequency (IF) signal, a detector 140 for detecting an audio signal from the IF signal, a multiplexer (MPX) demodulator 150 for separating a stereo signal into two left and right channels, And a control circuit 160 for detecting the reception sensitivity or electric field intensity from the IF signal level of the detector 140 and controlling the RF amplifier 100. The control circuit 160 outputs the detected reception sensitivity (S meter) to the controller 50.

  FIG. 7 is a block diagram illustrating the configuration of the surround generation unit according to the present embodiment. The surround generation unit 40 receives the two-channel stereo signal L / R, receives the decorrelation processing unit 200 that removes the correlation component of both signals, and the two-channel stereo signal L / R. An extraction unit 210 that extracts a signal, and an addition processing unit 220 that adds the signal that has been decorrelated by the decorrelation processing unit 200 and the low-frequency band signal that has been extracted by the extraction unit 210 are configured.

  The extraction unit 210 includes low-pass filters 212 and 214 that receive stereo signals L / R, respectively, and delay circuits 216 and 218 that delay signals output from the low-pass filters 212 and 214. The cut-off frequency of the low-pass filters 212 and 214 is preferably 200 Hz or less, and a low frequency band signal is extracted from the stereo signal L / R. The delay circuits 216 and 218 delay signal propagation by a time corresponding to the signal processing time by the decorrelation processing unit 200.

  FIG. 8 is a block diagram illustrating a configuration of the decorrelation processing unit. The decorrelation processing unit 200 generates the surround signal SL and the surround signal SR using the surround signal SL generation unit 310 and the surround signal SR generation unit 320. Surround signal SL generation section 310 receives stereo signal L, delay circuit 312 for delaying stereo signal L, stereo signal R, extracts a correlation component of stereo signal L from stereo signal R, and outputs stereo signal R An adaptive digital filter (ADF) 314 that performs decorrelation processing, an LMS (coefficient calculation unit) 316 that calculates filter coefficients of the ADF 314 by an LMS (least mean square) algorithm, and a difference between the output of the delay circuit 312 and the output of the ADF 314 is obtained. An adder circuit 318 is included, and a surround signal SL ′ is output from the adder circuit 318.

  The surround signal SR generation unit 320 inputs one stereo signal R, inputs a delay circuit 322 that performs a delay process of the stereo signal R, the stereo signal L, extracts a correlation component of the stereo signal R from the stereo signal L, An adaptive digital filter (ADF) 324 that performs decorrelation processing of the stereo signal L, an LMS (coefficient calculation unit) 326 that updates a filter coefficient of the ADF 324, and an adder circuit 328 that calculates a difference between the output of the delay circuit 322 and the output of the ADF 324 The surround circuit SR 'is output from the adder circuit 328.

  The ADFs 314 and 324 of the SL signal generation unit 310 and the SR signal generation unit 320 update the ADF coefficient W for each sample (for example, 1/44100 [sec] if the sampling frequency is 44.1 kHz). The coefficient update formula of ADFs 314 and 324 is expressed by formula (1).

Here, W is an ADF coefficient, μ is a step size parameter (a value between 0 and 1), e (n) is an error signal (= surround SL / SR signal), and x (n) is an input signal.

  In addition, the LMSs 316 and 326 of the SL signal generation unit 310 and the SR signal generation unit 320 calculate the coefficients using Expression (2) and Expression (3), respectively.

Further, e _SL (n) and e _SR (n) are expressed by Expression (4) and Expression (5).

  The addition processing unit 220 includes amplifiers 222 and 224 that adjust the gains of the output signals from the delay circuits 216 and 218, amplifiers 226 and 228 that adjust the gain of the output SL ′ / SR ′ from the decorrelation processing unit 200, An adder 230 that adds the output of the amplifier 222 and the output of the amplifier 226 and an adder 232 that adds the output of the amplifier 224 and the output of the amplifier 228 are included. By the adders 230 and 232, the low frequency band of the stereo signal L / R is blended with the decorrelated surround signal SL '/ SR' to generate the surround signal SL / SR.

  In the present embodiment, the low-frequency band that is deficient in the decorrelated surround signal SL ′ / SR ′ is enhanced by the low-frequency band signal extracted by the low-pass filter. Obtainable.

  Next, a second embodiment of the present invention will be described. FIG. 9 is a waveform of the surround output when the step size parameter μ of the decorrelation processing unit is varied. The surround signal SL ′ when the same pink noise is used for the stereo input L / R to the decorrelation processing unit 200 and the step size parameter μ is changed to 0.01 / 0.001 / 0.00001 is shown in FIG. 9 (a), (b) and (c).

  The decorrelation processing unit 200 has a role of a correlation removal filter, that is, a role of extracting a decorrelation component. The pink noise used as the input signal has the highest correlation (almost 1) because the input L / R is the same, so it can be said that there is almost no uncorrelated component. As a result, as can be seen from FIGS. 9A to 9C, the larger the step size parameter μ is, the more the correlation can be removed up to the high frequency range. The smaller the step size parameter μ is, the lower the remaining frequency range is. That is, it is possible to control the degree of extracting the decorrelation signal of the decorrelation processing unit by the step size parameter μ.

  In the above example, pink noise having a high correlation is input, but a music signal is actually input. Since the music signal adds reverberation, phase, and the like when the recording mixer mixes down, the correlation change becomes large. Accordingly, the output level of the entire band increases as compared with FIGS. 9A to 9C, but the correlation removal to the higher sound range is possible as the step size parameter μ is larger, and the lower sound region is obtained when the step size parameter μ is smaller. Maintain the relationship that will remain.

  In the second embodiment, the gains of the amplifiers 222, 224, 226, and 228 of the addition processing unit 220 (see FIG. 7) are varied according to the step size parameter. FIG. 10 is a diagram for explaining a preferable relationship between the step size parameter and the gain distribution. When the step size parameter is increased, the correlation component is removed from the low frequency range to the high frequency range, and it becomes difficult to extract the low frequency range of the surround signal SL ′ / SR ′. Therefore, the gains of the amplifiers 222 and 224 are increased. The gain of the audio signal in the low frequency band of the stereo signal L / R is increased. As a result, the low frequency range of the surround signal SL / SR is reinforced.

  On the other hand, when the step size parameter is reduced, a correlation component remains relatively in the surround signal SL '/ SR'. For this reason, the gains of the amplifiers 222 and 224 are made relatively smaller than the gains of the amplifiers 226 and 228, and the addition ratio of the audio signal in the low frequency band of the stereo signal L / R is made small.

Furthermore, the cutoff frequency of the low-pass filters 212 and 214 shown in FIG. 7 may be varied in conjunction with the amplifiers 222 and 224 or the step size parameter. That is, as shown in FIG.
When the gain is relatively increased, the cut-off frequency of the low-pass filters 212 and 214 is increased (for example, 200 Hz) so that the low frequency band is reinforced, and signals in a low frequency band of 200 Hz or less are added. To be. On the other hand, when the gains of the amplifiers 222 and 224 are relatively reduced, the cut-off frequency of the low-pass filters 212 and 214 is reduced (for example, 80 Hz), and signals in a low frequency band of 80 Hz or less are added. To. When the gains of the amplifiers 222 and 224 are at an intermediate level, or when the step size parameter is 0.0001, the cutoff frequency of the low-pass filters 212 and 214 is set to an intermediate range (for example, 150 Hz).

  In order to link the step size parameter and the gain of the amplifier, for example, as shown in the table of FIG. 11, a mode setting may be given to the in-vehicle audio apparatus. By selecting any one of modes 1, 2, and 3, the step size parameter is varied. For example, in mode 1, the step size parameter is increased to 0.001, and at this time, the gains of the amplifiers 226 and 228 are decreased and the gains of the amplifiers 222 and 224 are increased. In mode 2, the step size parameter is set to 0.0001, and the gains of the amplifiers 226 and 228 are made substantially equal to the gains of the amplifiers 222 and 224. In mode 3, the step size parameter is set to 0.00001, the gains of the amplifiers 226 and 228 are reduced, and the gains of the amplifiers 222 and 224 are increased.

  When the cut-off frequencies of the low-pass filters 212 and 214 are varied, as described above, in the mode 1, the cut-off frequency of the low-pass filter is set to the maximum so that the gains of the amplifiers 222 and 224 are increased. In mode 3, the cutoff frequency of the low-pass filter is minimized, and in mode 2, the cutoff frequency is intermediate between the maximum and minimum.

  The mode can be appropriately set by user input, and in accordance with the setting, the controller 50 (see FIG. 4) causes the surround generation unit 40 to input the step size parameter and the gain of the amplifier and the cutoff of the low-pass filter associated therewith. Gives a command to change the frequency. As a result, the bass or volume of the surround signal SL / SR can be changed according to the audio signal to be reproduced and the environment.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments according to the present invention, and various modifications can be made within the scope of the gist of the present invention described in the claims. Deformation / change is possible. In the above-described embodiment, an example in which a surround signal is generated from a stereo signal of FM broadcasting has been described. Of course, a surround signal may be generated and reproduced from a stereo signal other than this.

  The present invention is used in a video / audio apparatus for reproducing an audio signal received by radio broadcasting or television broadcasting.

It is a figure which shows the structural example of the adaptive decorrelator by the conventional FIR filter. It is a block diagram which shows the structure of the surround production | generation apparatus provided in the conventional vehicle-mounted audio apparatus. FIG. 3A shows the relationship between the sound range of the front FL / FR and the output level, and FIG. 3B shows the relationship between the sound range of the rear channel SL / SR and the output level. It is a block diagram which shows the structure of the vehicle-mounted audio apparatus which concerns on the Example of this invention. It is a figure which shows the layout of the speaker in vehicle interior space. It is a block diagram which shows the structure of a receiving module. It is a block diagram which shows the structure of the surround production | generation part of a present Example. It is a block diagram which shows the structure of the decorrelation process part of a present Example. It is a figure which shows the output waveform of surround signal SL when the step size parameter of a non-correlation processing part is varied. It is a figure which shows the preferable relationship between the step size parameter and gain distribution by 2nd Example of this invention. It is a table which shows the relationship between the mode of a vehicle-mounted audio apparatus, and a step size parameter.

Explanation of symbols

10: In-vehicle audio device 20: Antenna 30: Reception module 40: Surround generation unit 50: Controller 200: Uncorrelation processing unit 210: Extraction unit 212: Low-pass filter 214: Low-pass filter 216: Delay circuit 218: Delay circuit 220: Addition Processing units 222 to 228: amplifiers 230, 232: adder 310: SL signal generation unit 312: delay circuit 314: adaptive digital filter 316: LMS (coefficient calculation unit)
318: Adder circuit 320: SR signal generator 322: Delay circuit 324: Adaptive digital filter 326: LMS (coefficient calculator) 328: Adder circuit

Claims (9)

A surround generation device for generating a multi-channel surround signal from a two-channel stereo signal,
A decorrelation processing means for inputting a two-channel stereo signal, removing a correlation component of the stereo signal, and performing a decorrelation process of the stereo signal;
Extraction means for extracting a signal of a predetermined frequency band from a two-channel stereo signal;
Adding means for adding the extracted signal to the output signal of the decorrelation processing means and outputting a surround signal;
Control means for controlling the addition ratio by the addition means according to the variable step size parameter of the adaptive digital filter included in the decorrelation processing means;
A surround generation apparatus. The surround generation device according to claim 1, wherein the extraction unit extracts an audio signal in a low frequency band. The surround generation device according to claim 1, wherein the extraction unit includes a low-pass filter that can be set at a cutoff frequency of 200 Hz or less. The adding means includes a first amplifier that adjusts the gain of the signal extracted by the extracting means, and a second amplifier that adjusts the gain of the output signal of the decorrelation processing means, and the control means includes: The surround generation device according to claim 1, wherein gains of the first and second amplifiers are varied in accordance with variable step size parameters . The surround generation device according to any one of claims 1 to 4 , wherein the control unit increases the gain of the first amplifier in response to an increase in a step size parameter. The surround generation device according to any one of claims 1 to 5 , wherein the extraction unit varies a frequency band to be extracted in response to a gain of the first amplifier of the addition unit. The surround generation device according to claim 6 , wherein when the gain of the first amplifier is increased, the cutoff frequency of the low-pass filter is increased. The surround generation device according to any one of claims 1 to 7 , further comprising input means for instructing variable step size parameters. The surround generation device is mounted on a vehicle, and the two-channel stereo signal is output from left and right speakers of a front seat in the vehicle interior space, and the surround signal is output from left and right speakers of a rear seat of the vehicle interior space. The surround generation device according to any one of 1 to 8.

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