JP4427937B2 - Acoustic signal processing circuit and acoustic reproduction device - Google Patents

Description

【００８１】
なお、上記係数ｘ，ｙの算出方法において、偏移角度θの割り付けが困難な場合、上記算出方法に代わり、｜ＬＳ＋ＲＳ｜／｜ＬＳ−ＲＳ｜、あるいは｜ＬＳ−ＲＳ｜／｜ＬＳ＋ＲＳ｜の値から所定の近似式を求め、それを用いて係数ｘ，ｙを算出するようにしてもよい。
【００８２】
また、上記係数ｘ，ｙの算出方法において、ＤＳＰ（digital signal processor）が用いられる場合、一般に割り算に多くのステップを必要とするので、（ＬＳ＋ＲＳ）および（ＬＳ−ＲＳ）のそれぞれのレベルを、図１０に示すような左右シフト処理を用いて直接的な比較を行い、必要とするシフト数に応じてステップ的にθを割り当てる方法を用いてもよい。なお、図１０に示す左右シフト処理では、ａ＞ｂの場合、最初に現れる「１」がａと同じ桁になるまでｂの値を左にシフトしていき、必要となるシフト数に応じてステップ的にθを割り付ける。また、ａ≦ｂの場合は逆に右シフトを行う。また、シフト数に対応する係数ｘ，ｙのテーブルを用意しておいて、直接、係数ｘ，ｙを算出する方法を用いてもよい。さらには、係数ｘ，ｙが１サンプル期間でステップ的に変化するのが音声再生に不具合を生じるようであるなら、現在の係数ｘ，ｙから目的とする係数ｘ，ｙまで漸増および漸減処理を利用する方法を用いてもよい。
【００８３】
図７に戻り、レベル比較回路２８において算出された係数ｘ，ｙは、それぞれ定数積算回路２１〜２４において用いられる。すなわち、係数ｘは、定数積算回路２１，２３において用いられ、係数ｙは、定数積算回路２２，２４において用いられる。
【００８４】
定数積算回路２１，２２において係数ｘ，ｙが乗算された左サラウンドチャンネル信号ＬＳ同士は、その後、加算回路２６Ｌで加算され、仮想音像定位処理回路１４に供給される。また、定数積算回路２３，２４において係数ｘ，ｙが乗算された右サラウンドチャンネル信号ＲＳ同士は、加算回路２６Ｒで加算され、仮想音像定位処理回路１４に供給される。
【００８５】
このような処理によれば、図１１に示すように、サラウンドチャンネル信号ＬＳ，ＲＳがモノラル信号に近い場合は、上記した（ａ／ｂ）の値が大きくなり、拡散効果を付加するために、サラウンドチャンネル信号ＬＳ，ＲＳと前方チャンネル信号Ｌ，Ｃ，Ｒ間との間の相対位相差を約１５０°に近くなるようにする。一方、サラウンドチャンネル信号ＬＳ，ＲＳが互いに無相関あるいは逆相の場合は、（ａ／ｂ）の値が小さくなり、サラウンドチャンネル信号ＬＳ，ＲＳと前方チャンネル信号Ｌ，Ｃ，Ｒ間との間の相対位相差が小さくなるようにする。
【００８６】
したがって、サラウンドチャンネル信号ＬＳ，ＲＳに音源ソース側において予め位相差が付加されていても、サラウンドチャンネル信号ＬＳ，ＲＳと前方チャンネル信号Ｌ，Ｃ，Ｒ間との間の相対位相差を適度な位相差になるように設定変更することにより、仮想音像定位処理されたサラウンドチャンネル信号ＬＳ，ＲＳによって、拡がり感のある音場を提供することができる。
【００８７】
図７に戻り、仮想音像定位処理回路１４において仮想音像定位処理が施されたサラウンドチャンネル信号ＬＳ，ＲＳは、第１移相回路１１Ｌ，１１Ｒにおいて移相処理が施された前方チャンネル信号Ｌ，Ｒと、加算回路１５Ｌ，１５Ｒにおいてそれぞれ加算される。加算回路１５Ｌ，１５Ｒにおいてサラウンドチャンネル信号ＬＳ，ＲＳが加味された前方チャンネル信号Ｌ，Ｒは、第１移相回路１１Ｃにおいて移相処理が施され、かつ定数積算回路１７において定数が乗算された前方チャンネル信号Ｃと、加算回路１６Ｌ，１６Ｒでさらに加算され、前方中央チャンネル信号Ｃが加味された前方チャンネル信号Ｌv，Ｒvが出力端子から出力される。そして、上記前方チャンネル信号Ｌv，Ｒvは、増幅器７Ｒ，７Ｌによって増幅され、スピーカ装置Ｂから音響として出力される。
【００８８】
上記処理により、サラウンドチャンネル信号ＬＳ，ＲＳ同士の関係や、前方チャンネル信号との関係に左右されることなく、サラウンドチャンネル信号ＬＳ，ＲＳと前方チャンネル信号Ｌ，Ｃ，Ｒ間との間の相対位相差を適度な位相差にすることができるので、映画や音楽を問わず、様々な信号形態を有するマルチチャンネルソースに対して最適な仮想サラウンド再生を実現することができる。
【００８９】
なお、第１移相回路１１Ｌ，１１Ｃ，１１Ｒ，１１ＬＳ，１１ＲＳ、第２および第３移相回路１２，１３における、前方チャンネル信号Ｌ，Ｃ，Ｒ、およびサラウンドチャンネル信号ＬＳ，ＲＳに対する位相シフトは、上記したのと同様に、２００Ｈｚ程度から２ｋＨｚ程度の間で実現されればよい。
【００９０】
もちろん、この発明の範囲は上述した実施の形態に限定されるものではない。たとえば、音響信号処理回路は、上記実施形態における音響再生装置Ａに適用されることに限らず、たとえば車載用音響装置等、音響を出力するあらゆる装置に採用可能である。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る音響信号処理回路が適用される音響再生装置のブロック図である。
【図２】図１に示す音響信号処理回路のブロック図である。
【図３】オールパスフィルタの回路図である。
【図４】オールパスフィルタの回路図である。
【図５】オールパスフィルタの回路図である。
【図６】図１に示す音響信号処理回路における位相−周波数特性を示す図である。
【図７】他の音響信号処理回路のブロック図である。
【図８】係数算出処理を示すフローチャートである。
【図９】係数と偏移角度との関係を示す図である。
【図１０】係数の算出方法の一例を説明するための図である。
【図１１】図７に示す音響信号処理回路における位相−周波数特性を示す図である。
【図１２】従来の音響信号処理回路のブロック図である。
【図１３】従来の音響信号処理回路における位相−周波数特性を示す図である。
【符号の説明】
６ 音響信号処理回路
８Ｌ，８Ｒ スピーカ
１１Ｌ，１１Ｃ，１１Ｒ 第１移相回路
１２ 第２移相回路
１３ 第３移相回路
１４ 仮想音像定位処理回路
１５Ｌ，１５Ｒ 加算回路
Ａ 音響再生装置
Ｌ 前方左チャンネル信号
Ｒ 前方右チャンネル信号
ＬＳ 左サラウンドチャンネル信号
ＲＳ 右サラウンドチャンネル信号[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an acoustic signal processing circuit and an acoustic reproduction device for processing a multi-channel acoustic signal.
[0002]
[Prior art]
In recent years, an audio reproduction device having an acoustic signal processing circuit for processing a multi-channel acoustic signal has made it possible to experience a multi-channel audio experience full of realism even at home. Usually, in order to realize multi-channel sound, it is necessary to arrange three front speakers in front of the listener and two surround speakers on both sides or both sides behind the listener. Recently, a so-called virtual surround system has been developed that can give a listener a multi-channel audio experience with only two front speakers placed in front of the listener.
[0003]
In this virtual surround system, the phantom center sound image can be obtained by equally allocating the center channel signal to the front left and right channel signals with respect to the front center channel sound, so that the center channel sound can be easily realized. .
[0004]
Originally, a special process called a virtual sound image localization process is required to reproduce the left and right surround channel signals that localize the sound on both sides or both sides behind the listener with the left and right front speakers. In the virtual sound image localization processing, the sound output from the two speakers arranged in front is processed from the left and right surround speakers that are not actually arranged at the listener's ear position by processing using a human auditory mechanism. This is achieved by simulating the characteristics of the output voice. The left and right surround channel signals processed by the virtual sound image localization processing are mixed with the front left and right channel signals and can be reproduced by the left and right front speakers.
[0005]
In the method using the virtual sound localization processing, the listener can obtain an effect only in a place where the auditory mechanism is established in the positional relationship between the left and right front speakers and the listener, so the listener has a relatively narrow listening area called a sweet spot. You can only experience the effect. However, it is widely used as one feature due to a plurality of advantages such as that a sufficient effect can be expected for personal audition and that the system can be configured with only the same two speakers as the conventional stereo audition.
[0006]
The virtual sound image localization processing of the surround channel signal is not particularly problematic when there is no correlation with the originally input left and right surround channel signals, that is, when the surround channel signal is a stereo signal. However, when the surround channel signal is monaural, such as a matrix type Dolby surround, and even if the surround sound of the front 3 channels and the surround 2 channels is discrete, the left and right surround channel signals are effectively a monaural source. In many cases, the correlation between the left and right surround channel signals becomes very large and a good effect cannot be obtained.
[0007]
When playing back with the actual surround speakers placed on both sides of the listener or on both sides of the listener, the reflected sound on the wall or floor is added before the sound reaches the listener's ears, and the arrival time is subtly Because of the difference, at the position of the listener's ear, the degree of correlation of the signal decreases and the sound becomes slightly diffused. However, in the case of virtual sound image localization processing, only the direct sound and the arrival time from the front left and right speakers to the listener are the same, so the monaural sound remains highly correlated.
[0008]
In human hearing, sound image localization is likely to be mistaken on the median plane, and when a speaker is placed in front, the sound image is often recognized in front by helping the visual effect. Therefore, even when virtual sound image localization processing is performed on a monaural surround channel signal, the sound image is easily recognized in the listener's head or in front, and the listener's back or head, such as playback by an actual surround speaker, is used. The sound field is not diffused around.
[0009]
In order to avoid this problem, the virtual sound image localization processing generally employs a method in which the surround channel signal is previously uncorrelated. For decorrelation, it is common to use a phase shift process in order to maintain compatibility with stereo input.
[0010]
Mathematically, if a 90 ° phase difference is added between the left and right surround channel signals, the degree of correlation becomes “0”. Tend to be pulled. Further, when the phase difference is 180 ° (correlation degree: −1), a sense of spread is obtained, but a strong sense of reverse phase results in an unnatural sound image, resulting in a feeling of fatigue in a long-time audition.
[0011]
Further, when the phase difference is set to 150 °, the sense of reverse phase is not so much felt and there is a feeling of spread, and the tendency of the sound image to be pulled to one side is reduced. Therefore, a method has been proposed in which the relative phase difference of such surround channel signals is about 150 °.
[0012]
FIG. 12 is a diagram illustrating an example of an acoustic signal processing circuit for realizing the above method. According to this figure, the surround channel signals LS, RS are relative to each other by the phase shift circuits 31, 32. Phase difference Is set to about 150 °, and virtual sound image localization processing is performed by the virtual sound image localization processing circuit 33. Then, after being added by the front center channel signal C and the addition circuits 36L and 36R, which are added by the front channel signals L and R by the addition circuits 34L and 34R and multiplied by the constant by the constant integration circuit 35, for example, via an amplifier. Output from a speaker (both not shown). With this acoustic signal processing circuit, the phase-frequency characteristics shown in FIG. 13 are obtained.
[0013]
By the way, so-called Dolby Surround is a modified version of Dolby Stereo in a movie for consumer use. In both Dolby Surround and Dolby Stereo, the monaural surround channel signals are matrix-encoded on the front left and right channels so as to be in opposite phase to each other.
[0014]
When a movie using Dolby stereo is shown in a movie theater compatible with Dolby stereo, matrix decoding is performed to restore the original four channels, and a surround channel signal is also taken out. However, movies using Dolby Stereo are not only shown in Dolby Stereo compatible movie theaters, but may also be shown in stereo sound movie theaters and monaural sound movie theaters.
[0015]
Since audio encoded in Dolby Stereo is originally considered to be compatible with stereo playback, it can be played back without problems in a stereo audio movie theater. However, since a monaural sound movie theater mixes two encoded channel signals and reproduces them as monaural sound, the surround channel signal originally encoded in reverse phase is canceled and cannot be reproduced.
[0016]
Therefore, a certain guideline is provided so that important audio information is not mixed with only the surround channel signal at the time of signal mixing, and a part thereof is mixed with any one of the channel signals in front. By doing so, it is possible to avoid the problem that important audio information is lost in the monaural cinema.
[0017]
[Problems to be solved by the invention]
However, in the method using the acoustic signal processing circuit shown in FIG. 12, only the relative phase between the left and right surround channel signals is manipulated, so that the relative between the front channel signal and the surround channel signal as shown in FIG. The actual phase difference greatly changes depending on the frequency.
[0018]
In this case, there is no problem if there is no correlation between any one of the front channel signals and the surround channel signal. However, if the surround channel signal is partly mixed with one of the front channel signals, such as playback in a specific movie theater, it is correlated with either the surround channel signal or the front channel signal. There are certain signal components.
[0019]
Then, when the surround channel signal subjected to the phase shift process is subjected to the virtual sound image localization process and mixed with the front channel signal, it may interfere with the surround channel information originally mixed in the front channel signal. In this case, there is a possibility that the frequency band is emphasized in a certain frequency band or canceled in another frequency band due to the effect of the comb filter.
[0020]
The present invention has been conceived under such circumstances, and an acoustic signal processing circuit capable of solving the problem when there is a correlation between the front channel signal and the surround channel signal, and An object of the present invention is to provide a sound reproducing device including the same.
[0021]
DISCLOSURE OF THE INVENTION
In order to solve the above problems, the present invention takes the following technical means.
[0022]
The acoustic signal processing circuit provided by the first aspect of the present invention is an acoustic signal for mixing the left and right surround channel signals with the front left and right channel signals to be output to the speakers arranged at the front left and right of the listener. A first phase shifter that applies a phase shift of a reference angle to the front left and right channel signals, and one of the left and right surround channel signals; Second phase shifting means for providing a phase shift so as to have a phase difference of a first shift angle of about + 75 ° with respect to a reference angle of the phase shift given to the left and right channel signals, and the left and right surround channels The other surround channel signal among the signals is transferred to the front by the first phase shifting means. With respect to the reference angle of the given phase shift to the right channel signal so as to have relatively a phase difference of the second shift angle of about -75 °, and a third phase shifting means for providing a phase shift The first to third phase shifting means give a phase shift to each channel signal in a frequency band of at least 200 Hz to 2 kHz. It is characterized by that.
[0023]
According to a preferred embodiment, virtual sound image localization processing means for performing virtual sound image localization processing on the left and right surround channel signals to which a phase shift is given by the second phase shifting means and the third phase shifting means; First adding means for adding the one surround channel signal subjected to the virtual sound image localization processing by the virtual sound image localization processing means and one of the front left and right channel signals given the phase shift by the first phase shifting means; Second addition for adding the other surround channel signal subjected to the virtual sound image localization processing by the virtual sound image localization processing means and the other of the front left and right channel signals given phase shift by the first phase shifting means, respectively. Means.
[0025]
According to the present invention, the front left and right channel signals are mixed with the surround left and right channel signals and output from the speakers arranged on the front left and right of the listener. In this case, a phase shift of a reference angle is given to the front left and right channel signals, and a first deviation angle (about + 75 °) or a second deviation angle (−−) with respect to the reference angle is given to the surround left and right channel signals. A phase shift process is performed in which a phase shift is given so as to have a phase difference of about 75 °. Therefore, since a relative phase difference of, for example, 150 ° is obtained between the surround left and right channel signals, even if the surround left and right channel signals are monaural, if the surround left and right channel signals are subjected to virtual sound localization processing, the surroundings of the listener's head Can provide a wide sound field. In addition, a fixed relative phase difference of ± 75 ° is obtained between the surround front channel signal and the front left and right channel signals, for example, over a predetermined frequency range, so even if there is a correlation between both signals, Problems with frequency characteristics due to interference caused thereby can be solved.
[0026]
The sound reproduction device provided by the second aspect of the present invention is a sound signal processing for mixing the left and right surround channel signals with the front left and right channel signals to be output to the speakers arranged at the front left and right of the listener. A first phase shift means for respectively giving a phase shift of a reference angle to the front left and right channel signals and the left and right surround channel signals, and the left and right surround channel signals to which the phase shift is given by the first phase shift means. The first shift angle is different from the one surround channel signal, and the first shift channel signal has a first shift angle with respect to the reference angle of the phase shift given to the front left and right channel signals by the first phase shift means. A second counterpart that provides a phase shift so as to have a relative phase difference And the other surround channel signal of the left and right surround channel signals to which the phase shift is given by the first phase shift means, and the other surround channel signal is transferred to the front by the first phase shift means. A first phase shift is applied so as to have a phase difference of a second shift angle shifted in a direction opposite to the first shift angle with respect to the reference angle of the phase shift applied to the left and right channel signals. 3 phase shifting means, a setting means for setting a predetermined deviation angle based on the level ratio of the sum and difference of the left and right surround channel signals, and a coefficient based on the deviation angle set by the setting means. Coefficient calculation means for calculating, said one surround channel signal given a phase shift by said first phase shifting means, and said second phase shifting means A first coefficient multiplier for multiplying the one surround channel signal to which the phase shift is given by a coefficient calculated by the coefficient calculator, and the one multiplied by the first coefficient multiplier First surround means for adding together the surround channel signals, the other surround channel signal given a phase shift by the first phase shift means, and another phase shift given by the third phase shift means A second coefficient multiplier for multiplying the other surround channel signal by the coefficient calculated by the coefficient calculator, and the other surround channel signal multiplied by the second coefficient multiplier are added together. Second adding means for The first to third phase shifting means give a phase shift to each channel signal in a frequency band of at least 200 Hz to 2 kHz. .
[0027]
According to another preferred embodiment, the setting means sets the deviation angle to the first deviation angle or the second deviation angle when the sum of the left and right surround channel signals is larger than the difference between the left and right surround channel signals. When the sum of the left and right surround channel signals is smaller than the difference between the left and right surround channel signals, the deviation angle is set so as to approach the reference angle.
[0028]
According to another preferred embodiment, virtual sound image localization processing means for performing virtual sound image localization processing on the left and right surround channel signals added by the first addition means and the second addition means, and the virtual sound image localization processing A third adding means for adding the one surround channel signal subjected to the virtual sound image localization processing by the means and one of the front left and right channel signals given a phase shift by the first phase shifting means; and the virtual sound image And a fourth adding means for adding the other surround channel signal subjected to the virtual sound image localization processing by the localization processing means and the other of the front left and right channel signals given the phase shift by the first phase shifting means. .
[0030]
According to the present invention, when the left and right surround channel signals are close to a monaural signal, the sum of the left and right surround channel signals is larger than the difference between the left and right surround channel signals. In such a case, the left and right surround channel signals and the front channel signal are The relative phase difference between them is set to be close to, for example, about 150 °. On the other hand, when the left and right surround channel signals are uncorrelated or out of phase with each other, the sum of the left and right surround channel signals is smaller than the difference between the left and right surround channel signals. The relative phase difference of is made small. Therefore, even if a phase difference is previously added to the left and right surround channel signals on the sound source side, the relative phase difference between the left and right surround channel signals and the front left and right channel signals is moderate. Phase difference By changing the setting so that the sound field can be expanded, the left and right surround channel signals that have undergone virtual sound localization processing can provide a sound field with a sense of breadth, regardless of whether it is a movie or music. Virtual surround playback that is optimal for the source can be realized.
[0031]
The sound reproducing device provided by the third aspect of the present invention is characterized by including the sound signal processing circuit provided by the first aspect or the second aspect of the present invention.
[0032]
Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0034]
FIG. 1 is a diagram showing a block configuration of a main part of an audio reproduction device to which an audio signal processing circuit according to an embodiment of the present invention is applied. The sound reproducing device A is a device that can realize a so-called home theater, and for example, a pair of speaker devices B that output sound can be connected. In addition, a pair of speaker apparatus B is each arrange | positioned symmetrically in front right and left of a listener.
[0035]
The sound reproducing device A includes a CPU 1, a ROM 2, a RAM 3, an interface circuit 4, a DVD (digital versatile disc) reproducing device 5, an acoustic signal processing circuit 6, and amplifiers 7R and 7L. The CPU 1, the ROM 2, the RAM 3, and the interface The circuits 4 are bus-connected to each other.
[0036]
The CPU 1 controls the entire sound reproducing device A including the DVD reproducing device 5, the sound signal processing circuit 6, and the amplifiers 7R and 7L. That is, although not shown, the sound reproducing apparatus A is provided with an operation unit, a display unit, various sensors, and the like, and the CPU 1 controls the display unit and the like according to signals from the operation unit and the sensor. To do.
[0037]
The ROM 2 stores a program for operating the CPU 1, fixed data, and the like.
[0038]
The RAM 3 provides a work area for the CPU 1 and stores various data.
[0039]
The interface circuit 4 controls communication between the CPU 1 and the DVD playback device 5, the acoustic signal processing circuit 6, and the like.
[0040]
A DVD (digital versatile disc) playback device 5 plays back a DVD and is controlled by a control signal from the CPU 1 to rotate the DVD and output acoustic data such as music stored in the DVD. Note that the device for outputting acoustic data is not limited to the DVD playback device.
[0041]
The acoustic signal processing circuit 6, which will be described in detail later, is controlled by the CPU 1 to perform various processes on the acoustic data from the DVD playback device 5.
[0042]
The amplifiers 7R and 7L are controlled by the CPU 1 to amplify the acoustic signal from the acoustic signal processing circuit 6.
[0043]
The speaker device B is constituted by a plurality of box-like members that are independent from each other on the left and right sides, and includes, for example, a left channel playback speaker 8L and a right channel playback speaker 8R, respectively. The pair of speakers 8R and 8L convert the acoustic signals from the amplifiers 7R and 7L into sound. The speakers 8R and 8L have substantially the same acoustic characteristics.
[0044]
FIG. 2 is a diagram showing a circuit configuration of the acoustic signal processing circuit 6. The acoustic signal processing circuit 6 is a circuit for mixing the left and right surround channel signals LS and RS with the front left and right channel signals L and R, and includes a first phase shift circuit 11L, 11C and 11R, and a second phase shift circuit. 12, a third phase shift circuit 13, a virtual sound image localization processing circuit 14, addition circuits 15L, 15R, 16L, and 16R, and a constant integration circuit 17 are provided.
[0045]
The first phase shift circuits 11L, 11C, and 11R are circuits that perform phase shift processing that gives a phase shift of the same reference angle φ to the front channel signals L, C, and R. Here, the reference angle φ can be set to an arbitrary value.
[0046]
The second phase shift circuit 12 is a circuit that performs a phase shift process for giving a phase shift so that the left surround channel signal LS has a phase difference of the first shift angle relative to the reference angle φ. Specifically, the first shift angle is about + 75 ° (+ 70 ° to + 80 °) with respect to the reference angle φ.
[0047]
The third phase shift circuit 13 relatively has a phase difference of the second shift angle shifted in the direction opposite to the first shift angle with respect to the reference angle φ in the right surround channel signal RS. It is a circuit that performs a phase shift process for providing a phase shift. Specifically, the second deviation angle is about −75 ° (−70 ° to −80 °) with respect to the reference angle φ. Contrary to the above, a phase shift is given to the left surround channel signal LS so as to have a phase difference of the second deviation angle, and a first deviation angle of the right surround channel signal RS is given. A phase shift may be provided to have a phase difference. In short, the surround channel signals LS and RS may be prevented from being given a phase shift so as to have the same phase angle difference.
[0048]
The first phase shift circuits 11L, 11C, 11R, the second phase shift circuit 12, and the third phase shift circuit 13 can be realized by, for example, an analog circuit shown in FIG. Alternatively, it can be realized by a digital circuit having an all-pass filter (APF) which is a digital filter shown in FIG. In the case where the order is required, for example, as shown in FIG.
[0049]
Returning to FIG. 2, the virtual sound image localization processing circuit 14 virtually generates a sound image on the side of the listener, for example, with respect to the surround channel signals LS and RS to which the phase shift is given by the second and third circuits 12 and 13. This is a circuit for performing virtual sound image localization processing for localization.
[0050]
The adder circuits 15L and 15R are circuits that add the front channel signals L and R to which the phase shift is given by the first circuits 11L and 11R and the surround channel signals LS and RS subjected to the virtual sound image localization process.
[0051]
The addition circuits 16L and 16R are circuits for adding the front channel signals L and R to which the surround channel signals LS and RS are added and the front center channel signal C. That is, the front center channel signal C is branched after the constants are accumulated by the constant accumulation circuit 17, and each of the branched front center channel signals C is divided into the front channel signals L, R, RS added with the surround channel signals LS, RS. R is added to each.
[0052]
The constant integration circuit 17 multiplies the input signal by a predetermined constant. This constant is set by the CPU 1 and can be changed.
[0053]
With the above configuration, when the front channel signals L, C, and R are respectively input to the first phase shift circuits 11L, 11C, and 11R, the phase shift of the same reference angle φ is given to these signals.
[0054]
On the other hand, when the surround channel signals LS and RS are input to the second and third phase shift circuits 12 and 13, for example, the left surround channel signal LS has a first deviation angle (about + 75 ° with respect to the reference angle φ). ) To provide a phase shift. Further, for example, the right surround channel signal RS is given a phase shift so as to have a phase difference of a second deviation angle (about −75 °) with respect to the reference angle φ.
[0055]
The phase shifts for the front channel signals L, C, R and the surround channel signals LS, RS in the first phase shift circuits 11L, 11C, 11R and the second and third phase shift circuits 12, 13 For example, it may be realized between about 200 Hz and about 2 kHz that play an important role in sound source localization. That is, the relative phase difference may be gradually reduced at 200 Hz or lower and 2 kHz or higher, which is not related to sound source localization.
[0056]
The surround channel signals LS and RS subjected to the phase shift processing in the second and third phase shift circuits 12 and 13 are input to the virtual sound image localization processing circuit 14 and subjected to virtual sound image localization processing.
[0057]
The surround channel signals LS and RS subjected to the virtual sound image localization processing in the virtual sound image localization processing circuit 14 are the forward channel signals L and R subjected to the phase shift processing in the first phase shift circuits 11L and 11R and the addition circuit 15L. 15R, the left channels and the right channels are added.
[0058]
On the other hand, the front center channel signal C subjected to the phase shift processing in the first phase shift circuit 11C is multiplied by a constant such as “0.707” in the constant integration circuit 17. Thereafter, the front center channel signal C is branched and supplied to the adder circuits 16L and 16R, respectively. In the addition circuits 16L and 16R, the supplied front channel signal C is further added to the front channel signals L and R to which the surround channel signals LS and RS are added in the addition circuits 15L and 15R, and the front center channel signal C is added. The added front channel signals Lv and Rv are output from the output terminal.
[0059]
The front channel signals Lv and Rv are amplified by amplifiers 7R and 7L (see FIG. 1) and output as sound from the speaker device B, respectively.
[0060]
By such processing, as shown in FIG. 6, a relative phase difference of about 150 ° can be obtained between the surround channel signals LS and RS. Therefore, even if the surround channel signals LS and RS are monaural surround channel signals, a sound field spreading around the head of the listener can be provided by performing virtual sound image localization processing.
[0061]
In addition, a relative phase difference fixed at approximately ± 75 ° is maintained between the surround channel signals LS, RS and the front channel signals L, C, R over a wide frequency range (for example, 200 Hz to 2 kHz). Therefore, there is no peak / dip on the frequency characteristics due to the comb filter effect between the surround channel signals LS and RS originally mixed with the front channel signals L, C and R. Therefore, even when there is a correlation between the surround channel signals LS, RS and the front channel signals L, C, R, it is possible to avoid a problem in frequency characteristics due to interference caused by the correlation.
[0062]
By the way, multi-channel contents are expanded not only to the above-mentioned movie sources but also to music recording, and multi-channel music sources are increasing. In the case of sound in a movie, the surround channel signal is often used as a diffuse sound image in order to provide an ambience effect, and there are certain guidelines for mixing. There is no proper guideline and it is used relatively freely by the mixer. For this reason, the same signal having a phase difference with respect to the left and right surround channel signals is often mixed.
[0063]
For example, in the acoustic signal processing circuit 6 shown in FIG. 2 described above, relative phase differences are added to the surround channel signals LS and RS in the second and third phase shift circuits 12 and 13. For this reason, for example, when the surround channel signals LS and RS to which the phase difference has been added in advance are input to the acoustic signal processing circuit 6 in the circuit in the previous stage of the acoustic signal processing circuit 6, that is, on the sound source side (DVD playback device 5). As a result, the intended phase difference of the mixer cannot be obtained.
[0064]
That is, if a certain signal is mixed in advance so that the sound source side is in reverse phase with the surround channel signals LS and RS, virtual sound image localization processing is performed by the second and third phase shift circuits 12 and 13. A phase of about 30 ° cannot be inserted between the surround channel signals LS and RS. Therefore, when listening to the original source with an actual surround speaker, there is a sense of breadth, but when listening with the virtual sound localization processing, the sound field is almost close to a monaural surround signal and has no sense of breadth. Become.
[0065]
Therefore, by using the acoustic signal processing circuit shown below, a sound field with a sense of spread is realized even when the phase difference is previously given to the surround channel signals LS and RS on the sound source side. Yes.
[0066]
FIG. 7 is a diagram showing another acoustic signal processing circuit 60 different from the acoustic signal processing circuit 6 shown in FIG. The acoustic signal processing circuit 60 includes, in addition to the configuration in the acoustic signal processing circuit 6 described above, first phase shift circuits 11LS and 11RS, constant integration circuits 21, 22, 23, 24 and 25, addition circuits 26L and 26R, 27L and 27R and a level comparison circuit 28 are further provided.
[0067]
The first phase circuits 11LS and 11RS are circuits that perform a phase shift process that gives a phase shift of the same reference angle φ to the surround channel signals LS and RS, similarly to the first phase shift circuits 11L, 11C, and 11R. is there.
[0068]
The constant integration circuits 21, 22, 23, and 24 have a left surround channel signal LS and a reference angle φ that are given a phase shift so as to have a phase difference of a first deviation angle (for example, + 75 °) with respect to the reference angle φ. Left surround channel signal LS to which a phase shift is given, a right surround channel signal RS to which a phase shift is given so as to have a phase difference of a second deviation angle (for example, −75 °) with respect to the reference angle φ, and Left surround channel signal with phase shift given to reference angle φ LS Are multiplied by the coefficients x and y from the level comparison circuit 28, respectively.
[0069]
The adder circuits 26L and 26R add the left surround channel signals LS multiplied by the coefficients x and y and the right surround channel signals RS multiplied by the coefficients x and y, respectively.
[0070]
The constant integration circuit 25 multiplies the right surround channel signal RS supplied from the DVD playback device 5 by a constant “−1”.
[0071]
The adder circuit 27L adds the left surround channel signal LS and the right surround channel signal RS. The adding circuit 27R adds the left surround channel signal LS and the right surround channel signal RS multiplied by the constant “−1” by the constant integrating circuit 25.
[0072]
The level comparison circuit 28 adds the absolute value | LS + RS | of the sum of the left surround channel signal LS and the right surround channel signal RS added by the adder circuit 27L, and the left surround channel signal LS added by the adder circuit 27R. The absolute value | LS-RS | of the difference with the right surround channel signal RS is input, and the coefficients x and y are calculated by performing an appropriate calculation, and the coefficient x is calculated for the constant integration circuits 21, 22, 23, and 24. , Y.
[0073]
In operation, the left surround channel signal LS is supplied to the second phase shift circuit 12 and to the first phase shift circuit 11LS. The left surround channel signal LS supplied to the second phase shift circuit 12 is phase-shifted so as to have a phase difference of the first shift angle with respect to the reference angle φ, and is supplied to the constant integration circuit 21. On the other hand, the left surround channel signal LS supplied to the first phase shift circuit 11 LS is phase-shifted to the reference angle φ and supplied to the constant integration circuit 22.
[0074]
The right surround channel signal RS is supplied to the third phase shift circuit 13 and also to the first phase shift circuit 11RS. The right surround channel signal RS supplied to the third phase shift circuit 13 is given a phase shift so as to have a phase difference of the second shift angle with respect to the reference angle φ, and is supplied to the constant integration circuit 23. On the other hand, the right surround channel signal RS supplied to the first phase shift circuit 11RS is given a phase shift to the reference angle φ and supplied to the constant integration circuit 24.
[0075]
In each of the constant integration circuits 21 to 24, the surround channel signals LS and RS are multiplied by coefficients x and y given from the level comparison circuit 28. The coefficients x and y given from the level comparison circuit 28 are obtained by the following procedure, and will be described with reference to the flowchart shown in FIG.
[0076]
When surround channel signals LS and RS are input from the DVD playback device 5 (S1), addition processing and subtraction processing of both are performed. In other words, the left surround channel signal LS and the right surround channel signal RS are added by the addition circuit 27L to be added. The right surround channel signal RS is subtracted by adding a constant of “−1” by the constant integration circuit 25 and adding it to the left surround channel signal LS by the addition circuit 27R.
[0077]
Next, in the level comparison circuit 28, the absolute value | LS + RS | of the sum of the left surround channel signal LS and the right surround channel signal RS, and the left surround channel signal LS and the right surround channel signal RS added by the addition circuit 27R, The absolute value | LS−RS | of the difference between the two is obtained (S2). Then, | LS + RS | is set as a and | LS-RS | is set as b, and both a and b are compared (S3).
[0078]
Then, based on the comparison result between them, the shift angle θ is assigned (S4). However, the shift angle θ is set within a range of 0 ° to 75 °. For example, as shown in FIG. 9, when a >> b, specifically, when (a / b) ≧ 8-10, the shift angle θ is assigned to be large (close to 75 °). On the other hand, in the case of a << b, specifically, in the case of (a / b) ≦ 1 to 1.5, the shift angle θ is assigned to be small (close to 0 °). When the value of (a / b) is other than the above, an appropriate deviation angle θ is assigned.
[0079]
Next, when the shift angle θ is assigned, the coefficients x and y are respectively calculated by the following formula 1 (S5). FIG. 9 shows the relationship between the deviation angle θ and the coefficients x and y.
[0080]
[Expression 1]

[0081]
If it is difficult to assign the deviation angle θ in the calculation method of the coefficients x and y, instead of the calculation method, | LS + RS | / | LS-RS | or | LS-RS | / | LS + RS | A predetermined approximate expression may be obtained from the value, and the coefficients x and y may be calculated using the approximate expression.
[0082]
In addition, when a DSP (digital signal processor) is used in the calculation method of the coefficients x and y, since many steps are generally required for division, the levels of (LS + RS) and (LS-RS) are set as follows. A method may be used in which direct comparison is performed using a left / right shift process as shown in FIG. In the left-right shift process shown in FIG. 10, when a> b, the value of b is shifted to the left until “1” that appears first becomes the same digit as a, and according to the required number of shifts. Assign θ in steps. Conversely, when a ≦ b, a right shift is performed. Alternatively, a method may be used in which a table of coefficients x and y corresponding to the number of shifts is prepared and the coefficients x and y are directly calculated. Furthermore, if the coefficients x and y change stepwise in one sample period, it seems to cause a problem in sound reproduction, the gradual increase and decrease processes from the current coefficients x and y to the target coefficients x and y are performed. You may use the method to utilize.
[0083]
Returning to FIG. 7, the coefficients x and y calculated in the level comparison circuit 28 are used in the constant integration circuits 21 to 24, respectively. That is, the coefficient x is used in the constant integration circuits 21 and 23, and the coefficient y is used in the constant integration circuits 22 and 24.
[0084]
The left surround channel signals LS multiplied by the coefficients x and y in the constant integration circuits 21 and 22 are then added by the adding circuit 26L and supplied to the virtual sound image localization processing circuit 14. Further, the right surround channel signals RS multiplied by the coefficients x and y in the constant integration circuits 23 and 24 are added by the adding circuit 26R and supplied to the virtual sound image localization processing circuit 14.
[0085]
According to such processing, as shown in FIG. 11, when the surround channel signals LS and RS are close to monaural signals, the value of (a / b) described above becomes large, and in order to add a diffusion effect, The relative phase difference between the surround channel signals LS, RS and the front channel signals L, C, R is made to be close to about 150 °. On the other hand, when the surround channel signals LS and RS are uncorrelated or out of phase with each other, the value of (a / b) is small, and between the surround channel signals LS and RS and the front channel signals L, C and R. The relative phase difference is made small.
[0086]
Therefore, even if a phase difference is added in advance to the surround channel signals LS and RS on the sound source side, the relative phase difference between the surround channel signals LS and RS and the front channel signals L, C, and R is moderate. Phase difference By changing the setting so as to be, the surround sound field LS, RS subjected to the virtual sound image localization processing can provide a sound field with a sense of spread.
[0087]
Returning to FIG. 7, the surround channel signals LS and RS subjected to the virtual sound image localization processing in the virtual sound image localization processing circuit 14 are the front channel signals L and R subjected to the phase shift processing in the first phase shift circuits 11L and 11R. Are added in addition circuits 15L and 15R, respectively. The forward channel signals L and R to which the surround channel signals LS and RS are added in the adder circuits 15L and 15R are subjected to phase shift processing in the first phase shift circuit 11C and forward multiplied by a constant in the constant integration circuit 17. The channel signal C is further added by the adder circuits 16L and 16R, and the front channel signals Lv and Rv added with the front center channel signal C are output from the output terminal. The front channel signals Lv and Rv are amplified by the amplifiers 7R and 7L and output as sound from the speaker device B.
[0088]
By the above processing, the relative position between the surround channel signals LS, RS and the front channel signals L, C, R is not affected by the relationship between the surround channel signals LS, RS and the relationship with the front channel signals. Moderate phase difference Phase difference Therefore, it is possible to realize optimal virtual surround reproduction for multi-channel sources having various signal forms regardless of movies and music.
[0089]
The phase shifts of the first phase shift circuits 11L, 11C, 11R, 11LS, and 11RS and the second and third phase shift circuits 12 and 13 with respect to the front channel signals L, C, and R and the surround channel signals LS and RS are as follows. Similarly to the above, it may be realized between about 200 Hz and about 2 kHz.
[0090]
Of course, the scope of the present invention is not limited to the embodiment described above. For example, the acoustic signal processing circuit is not limited to being applied to the sound reproducing device A in the above-described embodiment, and can be employed in any device that outputs sound, such as an in-vehicle acoustic device.
[Brief description of the drawings]
FIG. 1 is a block diagram of an audio reproduction device to which an audio signal processing circuit according to an embodiment of the present invention is applied.
FIG. 2 is a block diagram of the acoustic signal processing circuit shown in FIG.
FIG. 3 is a circuit diagram of an all-pass filter.
FIG. 4 is a circuit diagram of an all-pass filter.
FIG. 5 is a circuit diagram of an all-pass filter.
6 is a diagram showing phase-frequency characteristics in the acoustic signal processing circuit shown in FIG. 1. FIG.
FIG. 7 is a block diagram of another acoustic signal processing circuit.
FIG. 8 is a flowchart showing a coefficient calculation process.
FIG. 9 is a diagram illustrating a relationship between a coefficient and a shift angle.
FIG. 10 is a diagram for explaining an example of a coefficient calculation method.
11 is a diagram showing phase-frequency characteristics in the acoustic signal processing circuit shown in FIG. 7. FIG.
FIG. 12 is a block diagram of a conventional acoustic signal processing circuit.
FIG. 13 is a diagram showing phase-frequency characteristics in a conventional acoustic signal processing circuit.
[Explanation of symbols]
6 Acoustic signal processing circuit
8L, 8R speaker
11L, 11C, 11R first phase shift circuit
12 Second phase shift circuit
13 Third phase shift circuit
14 Virtual sound image localization processing circuit
15L, 15R adder circuit
A Sound reproduction device
L Front left channel signal
R Front right channel signal
LS Left surround channel signal
RS Right surround channel signal

Claims (6)

An acoustic signal processing circuit for mixing left and right surround channel signals with front left and right channel signals to be output to speakers arranged at the front left and right of the listener,
First phase shifting means for respectively giving a phase shift of a reference angle to the front left and right channel signals;
The phase difference of the first deviation angle of about + 75 ° with respect to the reference angle of the phase shift given to the front left and right channel signals by the first phase shifting means to one of the left and right surround channel signals. Second phase shifting means for providing a phase shift so as to have
Of the left and right surround channel signals, the other surround channel signal has a second shift angle of about −75 ° with respect to the phase shift reference angle given to the front left and right channel signals by the first phase shifting means. Third phase shifting means for providing a phase shift so as to have a relative phase difference ,
The acoustic signal processing circuit according to claim 1, wherein the first to third phase shifting means give a phase shift to each channel signal in a frequency band of at least 200 Hz to 2 kHz . Virtual sound image localization processing means for performing virtual sound image localization processing on the left and right surround channel signals to which a phase shift is given by the second phase shifting means and the third phase shifting means;
First adding means for adding the one surround channel signal subjected to virtual sound image localization processing by the virtual sound image localization processing means and one of the front left and right channel signals given phase shift by the first phase shifting means. When,
Second adding means for adding the other surround channel signal subjected to virtual sound image localization processing by the virtual sound image localization processing means and the other of the front left and right channel signals given phase shift by the first phase shifting means. The acoustic signal processing circuit according to claim 1, comprising: An acoustic signal processing circuit for mixing left and right surround channel signals with front left and right channel signals to be output to speakers arranged at the front left and right of the listener,
First phase shifting means for giving a phase shift of a reference angle to each of the front left and right channel signals and the left and right surround channel signals;
Of the left and right surround channel signals to which a phase shift is given by the first phase shift means, a path different from one of the surround channel signals, and the one surround channel signal is transferred to the front left and right channels by the first phase shift means. Second phase shift means for providing a phase shift so as to have a phase difference of the first shift angle relative to a reference angle of the phase shift given to the signal;
Of the left and right surround channel signals that have been phase-shifted by the first phase shift means, the other surround channel signals are separated from the other surround channel signals by the first phase shift means and the front left and right channels. A third shift that gives a phase shift so as to have a phase difference of a second shift angle shifted in a direction opposite to the first shift angle with respect to the reference angle of the phase shift given to the signal. Phase means,
Setting means for setting a predetermined deviation angle based on the level ratio of the sum and difference of the left and right surround channel signals;
Coefficient calculating means for calculating a coefficient based on the deviation angle set by the setting means;
The coefficient calculation is performed on the one surround channel signal to which the phase shift is given by the first phase shift means and the one surround channel signal to which the other phase shift is given by the second phase shift means. First coefficient multiplication means for respectively multiplying the coefficients calculated by the means;
First addition means for adding the one surround channel signals multiplied by the first coefficient multiplication means;
The coefficient calculation is performed on the other surround channel signal to which the phase shift is given by the first phase shift means and the other surround channel signal to which the other phase shift is given by the third phase shift means. Second coefficient multiplying means for respectively multiplying the coefficients calculated by the means;
Second addition means for adding the other surround channel signals multiplied by the second coefficient multiplication means ,
The acoustic signal processing circuit according to claim 1, wherein the first to third phase shifting means give a phase shift to each channel signal in a frequency band of at least 200 Hz to 2 kHz . The setting means sets the deviation angle to be close to the first deviation angle or the second deviation angle when the sum of the left and right surround channel signals is larger than the difference between the left and right surround channel signals, 4. The acoustic signal processing circuit according to claim 3 , wherein when the sum of the left and right surround channel signals is smaller than the difference between the left and right surround channel signals, the deviation angle is set to be close to the reference angle. Virtual sound image localization processing means for performing virtual sound image localization processing on the left and right surround channel signals added by the first addition means and the second addition means;
Third adding means for adding the one surround channel signal subjected to virtual sound image localization processing by the virtual sound image localization processing means and one of the front left and right channel signals given phase shift by the first phase shifting means. When,
Fourth adding means for adding the other surround channel signal subjected to virtual sound image localization processing by the virtual sound image localization processing means and the other of the front left and right channel signals given phase shift by the first phase shifting means. comprising the door, the sound signal processing circuit according to claim 3 or 4. Characterized in that it comprises a sound signal processing circuit according to any one of claims 1 to 5, an audio reproducing device.

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