JPH11113098A - Two-channel encoding processor for multi-channel audio signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce only by two speakers arranged at the front side of a listener by executing sound image localization processing to collect to only the anterior sound of two channels right-left-symmetrical with respect to a listener to encode-process and preparing an audio program. SOLUTION: The audio signal of front-side two-channels L and R added with the audio signal of a center channel C outputted from adders 16L and 16R is added with rear-side two-channels SL and SR subjected virtual sound image processing by trans-oral technique through compressors 13L and 13R by adders 17L and 17R to obtain audio signal of two channels L0 and R0 . The encode processing of sound sonic localization for virtualization is executed to collect aud iosignals into only the front-side sound of two channels L0 and R0 right-left-symmetrical with respect to a listener to prepare the audio program. Consequently, it is possible to reproduce only by two speakers arranged at the front side of the listener without requiring a dedicated decoder at the time of reproducing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of audio signal channels, i.e., a so-called multi-channel.
It is intended to reproduce the audio signal of the number of channels exceeding the number of channels using only two speakers placed symmetrically in front of the listener. Particularly, the signal processing is performed at the time of creating the audio program, and at the time of reproduction, The present invention relates to a two-channel encoding processing apparatus for multi-channel audio signals that can be reproduced by two symmetrical speakers, which are commonly called stereo, in normal two-channel reproduction.

[0002]

2. Description of the Related Art Normally, for example, a sound track of a movie is encoded by a method called Dolby Surround or Dolby Digital, and is reproduced by an audio system having five channels. In addition, the Moving Picture Experts Group (MPEG), a standard for video and audio compression technology
M that handles multi-channels even among video compression methods
Recently, a format called PEG2 has been developed, and interest in multi-channel audio signals has increased worldwide.

[0003] In general, there are various types of surround processing. In some cases, the sound field is simply extended from a reproduction speaker to a two-channel stereo signal regardless of the contents of a program, depending on the phase and frequency characteristics. The sound is moved based on the screen, and this effect cannot be obtained unless clear multi-channel transmission is performed.

Taking the Torby digital system as an example, it converts a digital signal stream encoded in accordance with the Dolby Labs AC-3 system, as shown in FIG. Speaker 1 to the left of the position
L, speaker 1C on the center side, speaker 1R on the right side,
Speaker 1SL on the left and speaker 1S on the right
The five channels of signals Lch, Cch, Rch, SLch, and SRch are reproduced from speakers in which Rs are arranged. As shown in FIG. 4, a speaker 1SL2 is further provided at a position behind the listener, and a speaker 1SR2 is provided at the right side.
May be increased to 7 channels.

The present inventor has realized a convolver in which a filter coefficient based on a head-related transfer function is set for the rear channels SLch and SRch, and the rear channels SLch and SRch are located at symmetric rear positions with respect to the listener. Transaural (Tran) that performs filter processing to localize each sound image
A virtual sound field is created by a technique called “saural”, and the center channel Cch is distributed to two speakers arranged symmetrically in front of the listener so that the center channel Cch is reproduced only by two front speakers. The present invention has been made (Japanese Patent Application No. 8-253826).

[0006]

However, in the above-mentioned method, the target software program is limited to an encoded signal according to the AC-3 method of Dolby Laboratories, and a dedicated decoder conforming to the format is required on the reproducing side. However, since the system is complicated and costly, it was a heavy burden to easily enjoy it with PC software. This point is also the same for audio signals based on Dolby Surround or MPEG2, and when the number of channels becomes 7, the load will be further increased.

The present invention has been made in view of the above points, and performs an encoding process for virtualizing a multi-channel audio signal by using a transaural technique, thereby enabling a position in front of a listener without requiring a dedicated decoder during reproduction. It is an object of the present invention to obtain a two-channel encoding processing apparatus for a multi-channel audio signal which can be reproduced by only two speakers arranged in a multi-channel audio signal.

[0008]

To achieve the above object, a two-channel encoding apparatus for a multi-channel audio signal according to the present invention comprises a multi-channel audio signal comprising a plurality of channels for creating a sound field around a listener. It is characterized by comprising encoding processing means for performing a sound image localization process on a signal and collectively encoding only forward sounds of two channels symmetrical with respect to a listener to create an audio program.

Further, the encoding processing means realizes a convolver in which a filter coefficient based on a head-related transfer function is set for each of a pair of left and right rear channel audio signals of the multi-channel signal, and On the other hand, there is provided a sound image localization filter for performing a filter process to localize the sound image at each symmetric rear position.

[0010] The encoding processing means does not perform any processing on the forward sound of the two channels symmetrical to the listener, and performs an image processing on the forward sound of the two channels via the sound image localization filter. It is characterized by further comprising an adding means for respectively adding the pair of left and right rear channel audio signals subjected to the localization processing.

Further, the encoding processing means further includes a delay means for delaying an audio signal of a channel behind the multi-channel signal, and the sound image localization filter has been delayed through the delay means. A sound image localization process is performed on the audio signal of the rear channel.

Further, the encoding processing means further includes compressor means for performing a compression process on the pair of left and right sound signals subjected to the sound image localization processing, respectively, and the addition means includes a compressor for the two channel front sound. The sound signal of the rear channel which has been subjected to the compression processing via the compressor means is added.

[0013] The encoding processing means may include an attenuating means for attenuating a center channel audio signal of the multi-channel signal, and a center channel audio signal attenuated through the attenuating means for a two-channel forward sound. And an adding means for respectively adding

[0014] Further, a filter means is further provided between the attenuating means and the adding means, and a center channel sound signal subjected to localization processing is supplied to the adding means via the filtering means. Things.

[0015] Further, when the audio signal of the rear channel of the multi-channel signal is monaural, the encoding processing means delays the monaural signal by a predetermined amount, and delays the monaural signal via the delay means. A pseudo-stereo unit including an addition unit that obtains a sum signal and a difference signal of the signal and the monaural signal before the delay, and obtains a pair of rear channel audio signals that are uncorrelated with each other. It is assumed that.

Further, when the audio signal of the rear channel among the multi-channel signals is monaural, the encoding processing means delays the monaural signal by a predetermined amount, and delays the monaural signal via the delay means. A pair of pseudo-stereo means further comprising an adding means for obtaining a sum signal of the signal and the monaural signal before delay, and pseudo-stereo means having an inverting means for inverting the signal via the adding means, and having a non-correlation with each other. In which the audio signal of the rear channel is obtained.

Further, the encoding processing means includes monitoring means for monitoring the encoded two-channel audio signal, and operating means for providing an adjustment output for making the sound image localization natural to the sound image localization filter according to the monitoring result. It is characterized by having further.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the present invention, all processes are performed on the encoding side, and reproduction is to be performed in a normal 2-channel stereo. FIG. 1 is a configuration diagram showing a two-channel encoding apparatus for a multi-channel audio signal according to an embodiment of the present invention. In FIG. 1, reference numeral 10 denotes seven channels for creating a sound field around the listener in accordance with the positions of the listener and the speaker shown in FIG.
That is, the front two channels Lch and Rch, the center channel Cch, and the rear two channels SRch and SLc.
encoding processing means for performing sound image localization processing on a multi-channel audio signal composed of h, SR2ch, and SL2ch, and collectively encoding only forward sounds of two channels L ₀ and R ₀ symmetrical to the listener to create a sound program; Is shown. Although FIG. 1 shows a multi-channel audio signal of seven channels as an object, for simplicity of description, only the processing of SRch and SLch will be described for the rear sound, and the processing of SR2ch and SL2ch will be described for SRch and SLch. The description is omitted because it is the same as the processing of.

The encoding means 10 comprises a pair of left and right rear channels SR, S of the multi-channel signal.
For the L audio signal, filter processing is performed to realize a convolver in which filter coefficients P and N, which will be described later, are set based on the head-related transfer function for each channel, and to localize the sound image to the left and right symmetric rear positions with respect to the listener. The sound image localization filter 11 performs virtual processing by a transaural technique.

That is, as the sound image localization filter 11, as shown in FIG. 2, the same shuffler filter as disclosed in Japanese Patent Application No. 8-253826 is used. In FIG. 2, 11a ₁ is a first adder for obtaining a sum signal of the left and right pair of rear surround signals, 11a ₂ and the second adder for obtaining a difference signal of the left and right pair of rear surround signals, 11a ₃ will be described later filter first filter coefficient P processes the output of the adder 11a ₁ of the first set, 11a ₄ is of the second set is the filter coefficient N to be described later adder 1
Second filter, 11a ₅ is the first and the third adder to obtain a sum signal of the second filter processed signal, 11a ₆ is the first and the second filter for processing the output of 1a ₂ And a fourth adder that obtains a difference signal between the signals processed in step (a) and outputs the outputs of the third and fourth adders as a pair of left and right rear surround signals that have been subjected to the filter processing. Note that 11
a ₇ and 11a ₈ denote counting multipliers, usually having coefficients K1 and K
2 is set to 1.

Here, the filter coefficients P and N are given by P = (F + K) / (S + A) N = (F−K) / (SA), and S is received from a pair of speakers 1L and 1R. The transfer function to the ear on the same side of the listener, A is a pair of speakers 1
L, 1R to the transfer function from the ear on the other side of the listener, F is the transfer function from the position where the sound image is to be localized to the ear on the same side of the listener, and K is the transfer function from the position where the sound image is to be localized to the listener. The transfer function to the side ear is shown.

Returning to FIG. 1, the sound image localization filter 11
Rear rear surround signals SR and SL input to the
In order to improve the separation from the forward sound, the delay circuits 12R, 1
A signal delayed by several tens of msec with respect to the forward sound is input via the 2L. In the sound image localization processing by the sound image localization filter 11, a low sound component is enhanced. The signals subjected to the sound image localization processing output from the sound image localization filter 11 are processed by the compressors 13R and 13L, respectively.

On the other hand, the audio signals of the front two channels L and R are used without any processing as they are, and the audio signal of the center channel C is attenuated by -3 dB by the attenuator 14 and distributed to the left and right. 15L
After that, the signals are added to the sound signals of the front two channels L and R by the adders 16L and 16R. Further, the audio signals of the front two channels L and R to which the audio signal of the center channel C output from the adders 16L and 16R are added are added by the adders 17L and 17R.
The rear two virtual sound image processing performed by the transaural technology via the compressors 13L and 13R.
Channels SL and SR are added, and two channels L ₀ ,
An audio signal of R ₀ is obtained.

Further, the encoding processing means 1 shown in FIG.
In the case of 0, a monitor means (for example, a 2-channel speaker) 18 for monitoring the encoded audio signals of the two channels L ₀ and R ₀ , and the sound image localization filter 11 makes the localization natural according to the monitoring result. The creator is provided with an operation unit 19 for providing an adjustment output, and the creator can monitor the signals combined into two channels with a speaker while operating the operation unit 19.
By, for example, to be able to adjust the balance between left and right by providing a regulated output for adjusting the coefficients K1, K2 of the coefficient multipliers 11a _7, 11a ₈ Shah hula filter shown in FIG. 2 for each channel . Operation unit 1
Reference numeral 9 indicates that the delay amounts of the delay circuits 12R and 12L and the gain adjustment amounts to the compressors 13R and 13L can be adjusted for each channel. However, the gain fluctuations in the compressors 13R and 13L after the virtual sound image processing are linked to both channels in order to prevent the sound image from being distorted.

In this way, the sound image localization encoding process for virtualizing the five-channel audio signal using the transaural technique is performed, and the audio signal localization is performed symmetrically with respect to the listener.
Since the audio program can be created by combining only the forward sounds of the channels L ₀ and R ₀ , it is possible to play back only the two speakers arranged at the front position of the listener without requiring a dedicated decoder at the time of playback. Become.

In the above description, the multi-channel audio signal includes the front two channels Lch and Rch, the center channel Cch, the rear two channels SRch,
Although the above description relates to a 5-channel audio signal composed of SLch, as shown in FIG.
Also for the channels SR2ch and SL2ch, the sound image localization filter 11, the sound image localization filter 21, the delay circuits 22R and 22L, and the compressors 23R and 23L similar to the delay circuits 12R and 12L and the compressors 13R and 13L.
It is needless to say that the present invention can be similarly applied to a 7-channel audio signal by providing.

In the case of Dolby Surround or the 3-1 type audio system used in Japanese Hi-Vision TV, when the rear signal is a monaural signal and the surround signal of the rear channel among the multi-channel signals is monaural, FIG. ), A delay circuit 20a that delays the monaural surround signal S by a predetermined amount, and a sum signal of the monaural surround signal S via the delay circuit 20a and the monaural surround signal S before the delay. And pseudo-stereo unit 20-1 having adders 20b and 20c for obtaining a difference signal.
In order to further prepare for zero, surround signals SR and SL of a pair of rear channels which are not correlated with each other may be obtained and supplied to the delay circuits 12R and 12L, respectively.

As shown in FIG. 3B, a delay circuit 2 for delaying the monaural surround signal S by a predetermined amount.
0c, a sum signal of a delayed signal of the monaural surround signal S via the delay circuit 20c and a sum signal of the monaural surround signal S before the delay, and the adder 2d.
A pseudo-stereo unit 20-2 having an inverter 20f for inverting a signal via 0d is further provided in the encoding processing unit 10 shown in FIG. 1 so as to surround a pair of rear channels that are uncorrelated with each other. The signals SR and SL may be obtained and supplied to the delay circuits 12R and 12L, respectively.

As shown in FIG. 3 (c), the monaural surround signal S is output as it is, and the inverter 20 inverts the monaural surround signal S.
f is further provided in the encoding processing means 10 shown in FIG. 1 to obtain a pair of rear channel surround signals SR and SL which are not correlated with each other, and these are obtained. Each of the delay circuits 12R,
You may make it give to 12L.

[0030]

As described above, according to the present invention, the multi-channel audio signal is virtualized by using the transaural technique, the sound image localization is encoded, and the two channels L ₀ , R symmetric with respect to the listener. _Since it is possible to create an audio program collectively with only the forward sound of ₀ ,
At the time of reproduction, it is possible to reproduce with only two speakers arranged in front of the listener without requiring a dedicated decoder.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a two-channel encoding apparatus for a multi-channel audio signal according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a shuffler filter used as the sound image localization filter 11 of FIG.

FIG. 3 is a diagram illustrating three configuration examples of a pseudo-stereo circuit for performing pseudo-stereo conversion when a rear channel signal of a multi-channel audio signal is monaural;

FIG. 4 is an explanatory diagram showing an arrangement relationship of each speaker of a multi-channel audio signal with respect to a listener.

[Explanation of symbols]

1L, 1R, 1C, 1SL, 1SR, 1SL2, 1SL
2 Speaker 10 Encoding processing means 11 Sound image localization filter 12R, 12L Delay circuit 13R, 13L Compressor 14 Attenuator 15R, 15L Filter 16R, 16L, 17R, 17L Adder 18 Monitor 19 Operation unit 20-1, 20-2 Pseudo stereo circuit

Claims (11)

[Claims] 1. A sound image localization process is performed on a multi-channel audio signal composed of a plurality of channels to form a sound field around a listener, and the sound is obtained by encoding and processing only the frontal sound of two channels symmetrical to the listener. A two-channel encoding device for a multi-channel audio signal, comprising encoding processing means for creating a program. 2. The encoding processing means implements a convolver in which a filter coefficient based on a head-related transfer function is set for each channel of a pair of left and right rear channel audio signals of the multi-channel signal, and 2. The multi-channel audio signal two-channel encoding processing apparatus according to claim 1, further comprising a sound image localization filter for performing a filter process to localize the sound image at respective symmetric rear positions. 3. The encoding processing means does not perform any processing on a forward sound of two channels symmetrical to a listener, and performs an image processing on the forward sound of the two channels via the sound image localization filter. 3. The two-channel encoding apparatus for multi-channel audio signals according to claim 2, further comprising an adding means for adding the pair of left and right audio signals of the rear channel subjected to the localization processing. 4. The encoding processing means further comprises a delay means for delaying an audio signal of a channel behind the multi-channel signal, and the sound image localization filter is delayed by the delay means via the delay means. 4. The two-channel encoding apparatus for multi-channel audio signals according to claim 2, wherein a sound image localization process is performed on the audio signal of the rear channel. 5. The encoding processing means further comprises compressor means for performing a compression process on each of a pair of left and right rear sound signals subjected to the sound image localization processing. The two-channel encoding apparatus for multi-channel audio signals according to claim 3 or 4, wherein the rear-channel audio signals that have been subjected to the compression processing via the compressor unit are respectively added. 6. The encoding processing means includes: attenuating means for attenuating a center channel audio signal of the multi-channel signal; and a center channel audio signal attenuated by attenuating two channel forward sounds through the attenuating means. 6. The two-channel encoding apparatus for multi-channel audio signals according to claim 3, further comprising: an adding unit for adding. 7. Between the attenuation means and the addition means,
7. The two-channel encoding apparatus for multi-channel audio signals according to claim 6, further comprising a filter means, wherein the center channel audio signal subjected to the localization processing is supplied to said addition means via said filter means. 8. The encoding processing means includes: delay means for delaying the monaural signal by a predetermined amount when the audio signal of the rear channel of the multi-channel signal is monaural; and delaying the monaural signal via the delay means. A pseudo-stereo unit including an addition unit that obtains a sum signal and a difference signal of the signal and the monaural signal before the delay, and obtains a pair of rear channel audio signals that are uncorrelated with each other. 8. A two-channel encoding apparatus for multi-channel audio signals according to claim 1, wherein: 9. The encoding processing means includes: delay means for delaying the monaural signal by a predetermined amount when the audio signal of the rear channel of the multi-channel signal is monaural; and delaying the monaural signal via the delay means. A pair of pseudo-stereo means further comprising an adding means for obtaining a sum signal of the signal and the monaural signal before delay, and pseudo-stereo means having an inverting means for inverting the signal via the adding means, and having a non-correlation with each other. 8. The two-channel encoding apparatus for multi-channel audio signals according to claim 1, wherein an audio signal of the rear channel is obtained. 10. The encoding processing means includes means for outputting the monaural signal as it is when the audio signal of the rear channel of the multi-channel signal is monaural, and inverting means for inverting the monaural signal. The two-channel multi-channel audio signal according to any one of claims 1 to 7, further comprising pseudo-stereo means for obtaining a pair of rear-channel audio signals that are uncorrelated with each other. Encoding processing device. 11. The encoding processing means comprises: monitoring means for monitoring the encoded two-channel audio signal; and operating means for providing an adjustment output for making the sound image localization natural to the sound image localization filter in accordance with the monitoring result. The two-channel encoding apparatus for multi-channel audio signals according to any one of claims 2 to 10, further comprising: