JP2006319801A - Virtual surround decoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the S/N of a reproduced sound when applying a virtual surround decode processing to a multichannel signal obtained by a matrix surround decode processing so as to generate a virtual surround signal. <P>SOLUTION: A virtual surround decoder disclosed herein includes: a matrix surround decoder for generating multichannel source signals from two-channel input source signals; a virtual surround decoder for generating two-channel virtual surround signals from the multichannel source signals; and a correction section for correcting a level of the virtual surround signals. When the matrix surround decoder performs attenuation processing in this way, the level of the virtual surround signals is corrected in a way of supplementing the attenuated component so as to enhance the S/N of the reproduced sound. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a virtual surround decoder device.

  In recent years, a matrix surround decoding technique has been developed to expand and reproduce a 2-channel (ch) stereo source to a multi-channel source such as 5.1 ch. A stereo sound effect can be realized by generating a multi-channel source acoustic signal from a 2ch source such as a CD by conventional stereo recording using a matrix surround decoder and performing surround reproduction.

  In general, multi-channel playback devices such as AV amplifiers and DVD players are equipped with left and right front, center, left and right from digital audio data recorded on DVD (Digital Versatile Disc) and CD (Compact Disc) recorded in multi-channel Surround and source (sound) signals of each channel of the subwoofer are generated. Then, the multi-channel playback device outputs the multi-channel source signal to five or more speakers respectively arranged around the listener, thereby forming a realistic three-dimensional sound field.

  On the other hand, when listening to stereophonic sound reproduced by such a multi-channel playback device with headphones, it is necessary to regenerate a 2-channel source signal by synthesizing a multi-channel source signal generated from digital audio data. . The synthesis of a multi-channel source signal into a 2-channel source signal is called “stereo downmix”. By playing the 2ch source signal obtained by stereo downmix with the left and right headphones, the listener can hear the 3D sound full of realism similar to the surround system with headphones (such headphones are "surround headphones" ").

  Note that converting a multi-channel source signal into a source signal having a smaller number of channels is called “virtual surround decoding processing”, and the resulting signal is called “virtual surround signal”. The above stereo downmix is an example of a virtual surround decoding process.

  Examples of the above stereo downmix and surround headphones are described in Patent Documents 1 and 2.

JP 2003-333699 A JP 2003-333700 A

  The matrix surround decoder is configured to perform a matrix surround decoding process after normally applying an attenuation process of 3 dB to each input signal in order to prevent signal level clipping in the matrix process. . Therefore, for example, in order to realize the surround headphones as described above, when the virtual surround decoding process such as stereo downmix is performed on the multi-channel source signal obtained by the matrix surround decoding process, the matrix surround decoding process is performed. Since the signal level has been previously attenuated, the signal level of the obtained virtual surround signal is also attenuated, and there is a problem that the S / N of the reproduced sound is deteriorated.

  Examples of the problems to be solved by the present invention include the above. An object of the present invention is to improve S / N when a virtual surround signal is generated by performing a virtual surround decoding process on a multi-channel signal obtained by a matrix surround decoding process.

  According to the first aspect of the present invention, the virtual surround decoder device includes a matrix surround decoder that generates a multichannel source signal from a two-channel input source signal, and a virtual that generates a virtual surround signal from the multichannel source signal. A surround decoder and a level correction unit that corrects the level of the virtual surround signal are provided.

  In a preferred embodiment of the present invention, a virtual surround decoder device includes a matrix surround decoder that generates a multi-channel source signal from a 2-channel input source signal, and a virtual surround signal that generates a virtual surround signal from the multi-channel source signal. A surround decoder; and a level correction unit that corrects the level of the virtual surround signal.

  The virtual surround decoder device includes a matrix surround decoder that generates a multi-channel source signal from a 2-channel input source signal. The two-channel input source signal can be, for example, a surround-encoded stereo signal or a normal non-encoded stereo signal. The multi-channel source signal includes, for example, left and right front signals, a center signal, and left and right surround signals. A virtual surround decoder arranged after the matrix surround decoder generates a virtual surround signal from a multi-channel source signal. The virtual surround decoder can be, for example, a stereo downmix processor of a Dolby headphone system, and the virtual surround signal can be, for example, a 2-channel surround headphone output signal for headphone playback. The level of the virtual surround signal is corrected by the level correction unit. Thus, even when the input signal is attenuated in the matrix surround decoder, the level of the virtual surround signal can be corrected so as to compensate for the attenuation, and the S / N of the reproduced sound is improved.

  In one aspect of the virtual surround decoder device, the matrix surround decoder performs a matrix operation on an attenuation processing unit that attenuates the input source signal of the two channels by a predetermined level, and the input source signal of the two channels after the attenuation processing. An arithmetic unit that generates the multi-channel source signal, and the level correction unit increases the level of the virtual surround signal by the predetermined level.

  In this aspect, in the virtual surround decoder, attenuation processing is performed on the input source signals of two channels prior to the matrix operation. Therefore, the virtual surround decoder can improve the S / N by increasing the level of the virtual surround signal by the amount of attenuation.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a virtual surround decoder apparatus according to an embodiment of the present invention. In FIG. 1, a virtual surround decoder device 100 includes a digital audio interface receiver (DIR) 10, a matrix surround decoder 11, a stereo downmix processor 12, a microprocessor 13, and a digital audio data level correction unit (hereinafter simply referred to as “digital audio interface receiver”). 14), a D / A converter 15, and a transmission modulation unit 16.

  2ch digital audio data D output from various audio devices as input sources is input to the DIR 10. Here, the 2ch digital audio data refers to a surround-encoded stereo signal or a normal unencoded stereo signal.

  The DIR 10 extracts and demodulates the clock CK and data DT from the digital audio data D, and outputs the demodulated clock CK and data DT to the matrix surround decoder 11. The data DT includes left channel data Lt and right channel data Rt.

  The matrix surround decoder 11 uses a matrix surround decoding technique to generate a left front signal L, a right front signal R, a center signal C, a left surround signal Ls, and a right surround signal from 2ch data DT input from the DIR 10 according to a clock CK. A 5.1 channel signal including Rs and the subwoofer signal LFE is generated and output to the stereo downmix processor 12.

  Here, the matrix surround decoder 11 will be described in detail. FIG. 2 is a block diagram showing a configuration of a Dolby Pro Logic II decoder as an example of the matrix surround decoder 11. As shown, the matrix surround decoder 11 includes a matrix decoder 111, audio delay circuits 112L and 112R, a shelf or 7 kHz LPF 113L and 113R, a center width controller and bus management circuit 114, a volume and balance circuit 115, dimensions, A panorama and auto balance circuit 116 and a noise sequencer 117 are provided.

  The matrix decoder 111 extracts and outputs the main five-channel signals, that is, the front signals L and R, the center signal C, and the surround signals Ls and Rs from the 2-channel data DT (Lt, Rt) input from the DIR 10. To do. Specifically, the matrix decoder 111 generates a main 5-channel signal by a steering logic (direction enhancement technique) that performs matrix calculation based on the input 2ch data Lt and Rt.

  The generated front signals L and R and the center signal C are input to the center width controller and bus management circuit 114. On the other hand, the surround signals Ls and Rs are supplied to the audio delay circuits 112L and 112R, respectively. The surround signals Ls and Rs are supplied to the center width controller and the bus management circuit 114 via the audio delay circuits 112L and 112R, the shelf, or the 7 kHz LPFs 113L and 113R, respectively.

  The center width controller and bus management circuit 114 performs center width control as necessary, generates a subwoofer signal LFE, and supplies the main 5-channel signal and the subwoofer signal LFE to the volume and balance circuit 115. The volume and balance circuit 115 adjusts the volume of the signal of each channel and the balance between the signals, and outputs the signal of each channel.

  The dimension, panorama and auto balance circuit 116 is connected to the matrix decoder 111, and performs dimension control, panorama control and auto balance mode switching of the matrix decoder 111. In addition, the noise sequencer 117 outputs noise sequentially from the speakers of each of the L, C, R, Ls, and Rs channels, and adjusts the speaker volume of each channel and adjusts the speaker distance (that is, the delay time). This is used when making adjustments.

  The Dolby Pro Logic II decoder has a virtual mode, a prologic emulation mode and a matrix mode in addition to a movie mode suitable for playback of movie sources and general 2ch source signals, and a music mode suitable for playback of stereo music signals. Have. The functional characteristics in each mode are shown in FIG.

  In FIG. 3, “surround delay” is a delay given to the surround signals Ls and Rs by the audio delay circuits 112L and 112R, and the amount of delay differs for each mode. “Surround filter” indicates a filter process executed by a shelf or 7 kHz LPFs 113L and 113R arranged at the subsequent stage of the audio delay circuits 112L and 112R. A shelf filter is used in the music mode and the matrix mode, and a 7 kHz LPF is used in the prologic emulation mode. “Unified surround channel” is used in the movie mode, and surround speakers are in phase.

  “Panorama control” extends the stereo image of the front to the surround speakers and produces a wrapping effect by the side sound image. “Dimension control” shifts the sound field to the front side or the surround side (rear side) to adjust the level difference between the front side and the rear side. "Center width control" distributes the signal components of the center to the front left and right speakers so as not to concentrate on the center. “Auto balance” automatically controls the balance between the front left and right speakers based on the center signal C. The panorama control, dimension control and auto balance control are executed by the dimension, panorama and auto balance circuit 116 shown in FIG. Center width control is executed by the center width controller and bus management circuit 114.

  Returning to FIG. 1, the stereo downmix processor 12 converts the left front signal L, the right front signal R, the center signal C, the left surround signal Ls, the right surround signal Rs, and the subwoofer signal LFE into preset downmix coefficients. 2ch surround headphone output signals Lo and Ro are generated. An example of a signal synthesis formula by a stereo downmix processor is shown below.

Lo = α (L + 0.707C + Ls + LFE)
Ro = α (R + 0.707C + Rs + LFE) (1)
Note that “α” is called an attenuation coefficient, and when the signal level of each channel simultaneously increases, the gains of the surround headphone output signals Lo and Ro exceed “1” and the reproduced sound from the headphones is clipped. It is used in order to prevent it. The surround headphone output signals Lo and Ro obtained in this way are supplied to the level correction unit 14. Note that the processing by the stereo downmix processor corresponds to virtual surround processing, and the surround headphone output signals Lo and Ro obtained thereby correspond to virtual surround signals.

  The microprocessor 13 acquires information on the sampling frequency (FS) included in the digital audio data D from the DIR 10, and determines the type of the input source based on the acquired information on the sampling frequency. Based on the determination result, the mode control signal Sc1 indicating one of the above-described modes (movie mode, music mode, etc.) is supplied to the matrix surround decoder 11. Further, even when the user manually selects a mode, the microprocessor 13 supplies a mode control signal Sc1 indicating the mode to the matrix surround decoder 11. The matrix surround decoder 11 executes each function described with reference to FIG. 3 based on the mode control signal Sc1.

  Further, the microprocessor 13 supplies the correction control signal Sc2 to the level correction unit 14. The level correction unit 14 corrects the levels of the surround headphone output signals Lo and Ro based on the correction control signal Sc2 given by the microprocessor 13. The level correction amount indicated by the correction control signal Sc2 basically depends on the attenuation process executed by the matrix surround decoder 11. The matrix surround decoder 11 executes attenuation processing for attenuating the levels of the left and right channel data Lt and Rt by a predetermined attenuation amount (for example, 3 dB) prior to matrix processing in order to prevent signal level clipping from occurring in matrix processing. To do. Therefore, the surround headphone output signals Lo and Ro obtained by the stereo downmix processor 12 are attenuated by a predetermined level as compared with the input audio data DT (Lt and Rt). Has fallen. Therefore, the microprocessor 13 supplies the level correction unit 14 with the correction control signal Sc2 indicating the level correction amount (3 dB in the above example) corresponding to the amount attenuated by the matrix surround decoder 11. As a result, the levels of the surround headphone output signals Lo and Ro are corrected by the same amount, and the S / N of the reproduced sound is improved. The corrected output signals Loc and Roc are supplied to the D / A converter 15 and the transmission modulation unit 16, respectively.

  The D / A converter 15 is connected to a speaker or the like via an amplifier (not shown) and the like, and surround headphone output signals Loc and Roc are reproduced. The transmission modulation unit 16 is a modulation unit for digital audio data transmitted to wireless headphones, and a modulated signal is transmitted to wireless headphones (not shown). As the transmission modulation, for example, FM modulation or predetermined digital modulation can be used.

  As described above, the virtual surround decoder device 100 includes the matrix surround decoder 11 that generates a multi-channel source signal from a 2-channel input source signal, and the stereo downmix that generates a surround headphone output signal from the multi-channel source signal. The processor 12 and a level correction unit 14 that corrects the level of the surround headphone output signal are provided. Therefore, even when the input signal is attenuated in the matrix surround decoder, the level of the surround headphone output signal can be corrected so as to compensate for the attenuation, and the S / N of the reproduced sound is improved. Further, since the S / N of the surround headphone output signals Lo and Ro is ensured, the S / N in the transmission processing from the transmission modulation unit 16 to the wireless headphones can also be ensured.

[Modification]
In the above example, the correction amount by the level correction unit 14 is the attenuation amount of the attenuation process executed by the matrix surround decoder 11 (3 dB in the above example). In addition, the level correction amount by the level correction unit 14 may be determined in consideration of the attenuation amount by the stereo downmix processor 12, that is, the value of the attenuation coefficient α. Specifically, the level correction amount by the level correction unit 14 may be set to the sum of the predetermined attenuation amount executed by the matrix surround decoder 11 and the attenuation amount (attenuation coefficient α) by the stereo downmix processor 12. .

It is a block diagram which shows the structure of the virtual surround decoder apparatus based on the Example of this invention. It is a block diagram which shows the structure of a Dolby prologic II decoder as an example of a matrix surround decoder. It is a graph which shows the functional characteristic of the output mode of a matrix surround decoder.

Explanation of symbols

10 DIR
11 Matrix Surround Decoder 12 Stereo Downmix Processor 13 Microprocessor 14 Digital Audio Data Level Correction Unit 15 D / A Converter 16 Transmission Modulation Unit 100 Virtual Surround Decoder Device 111 Matrix Decoder

Claims (2)

A matrix surround decoder that generates a multi-channel source signal from a 2-channel input source signal;
A virtual surround decoder that generates a virtual surround signal from the multi-channel source signal;
A virtual surround decoder device comprising: a level correction unit that corrects the level of the virtual surround signal. The matrix surround decoder is configured to attenuate the two-channel input source signal by a predetermined level, and to perform a matrix operation on the two-channel input source signal after the attenuation processing to generate the multi-channel source signal. And
The virtual surround decoder device according to claim 1, wherein the level correction unit increases the level of the virtual surround signal by the predetermined level.

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