Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1998-05-15
2003-01-14
Harvey, Minsun Oh (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S001000, C381S061000
Reexamination Certificate
active
06507657
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a stereophonic sound image enhancement apparatus and a stereophonic sound image enhancement method, capable of enhancing a stereophonic sound image during a stereophonic sound reproducing operation. The apparatus and methods may be used in, for example, electronic music instruments, game machines, and acoustic appliances (for example, mixers). More specifically, the present invention is directed to a technique for enhancing stereophonic sound images during a 2-channel speaker reproducing operation.
2. Description of the Related Art
Several conventional sound image localizing techniques are known in this field. For example, in one technique, a left channel signal and a right channel signal for a stereophonic sound are produced and supplied to left/right speakers, respectively, to produce stereophonic sounds simultaneously so that a sound image is localized. Essentially, this conventional sound image localizing technique localizes the sound image by changing the balance in the sound volumes of the left/right channels. As a consequence, the sound image is localized only between the left speaker and the right speaker.
Another sound image localizing technique has been developed where a sound that a phase of a right-channel signal is inverted and is mixed with a left-channel signal and a phase of the left-channel signal is inverted and is mixed with the right-channel signal. As a consequence, the resulting sound image is localized at any position except for positions between the left speaker and the right speaker (namely, a left side, or a right side located apart from left/right speakers). This sound image localizing technique is disclosed in, for instance, “SOUND IMAGE MANIPULATION APPARATUS AND METHOD FOR SOUND IMAGE ENHANCEMENT” of WO94/16538 (PCT/US93/12688).
This conventional sound image manipulation apparatus/method for sound image enhancement produces a difference signal between a left-channel input signal and a right-channel input signal. The amplitude or magnitude of this difference signal is adjusted, and the adjusted difference signal is supplied to a band-pass filter. Then, the difference signal filtered by the band-pass filter is added to the left-channel input signal to produce the left-channel output signal. Similarly, the difference signal filtered from the band-pass filter is subtracted from the right-channel input signal to produce the right-channel output signal. The left-channel output signal and the right-channel output signal are supplied to the left speaker and the right speaker, respectively. According to the conventional sound image manipulation apparatus and sound image enhancement method, the sound image can be localized at any position except for positions between the left speaker and the right speaker. As a consequence, the stereophonic sound image is enhanced and a sound stage having excellent presence may be realized.
However, these sound image manipulation apparatus and sound image enhancement methods may have a problem in that when the enhancement effect of the stereophonic sound image is increased by controlling the amplitude of the difference signal the sound quality may be deteriorated. In the worst case, the sound quality would be deteriorated to such an extent that the inputted source could not be reproduced.
Also, the Schroeder method is known in this field as another technique capable of localizing the sound image at any position except for the position between the left speaker and the right speaker. In the Schroeder method, crosstalk sounds from the left speaker to a right ear and from the right speaker to a left ear are canceled. As a result, a listening condition using a headphone may be established. When the Schroeder localizing technique is introduced, the sound image can be localized at any arbitrary position such as positions immediately beside a listener, immediately behind a listener, and also between the left speaker and the right speaker.
However, if a sound image localization apparatus to which the basic idea of this Schroeder method has been strictly applied is constituted by an analog circuit, then a huge amount of hardware is necessarily required. On the other hand, if this sound image localization apparatus is arranged by a digitally-operated processor such as a digital signal processor (DSP) and a CPU, then a large amount of data processing operation is required. As a result, conventionally, the sound image localization apparatus with employment of the Schroeder method is allowed to be applied only to such a limited appliance, for instance, high-grade electronic musical instruments, game machines, and acoustic appliances.
SUMMARY OF THE INVENTION
As a consequence, the present invention has an object to provide a stereophonic sound image enhancement apparatus and a stereophonic sound image enhancement method, capable of enhancing a stereophonic sound image without deteriorating a sound quality during a 2-channel speaker reproducing operation. Furthermore, another object of the present invention is to provide a stereophonic sound image enhancement apparatus and a stereophonic sound image enhancement method, which can be made by a simple circuit arrangement and at low cost.
To achieve the above explained object, as indicated in
FIG. 1
, a stereophonic sound image enhancement apparatus, according to a first aspect of the present invention, includes:
a first all-pass filter
10
a
for changing a phase of a left channel input signal Lin in response to a frequency of the left channel input signal Lin to thereby output a phase-changed left channel input signal;
a second all-pass filter
10
b
for changing a phase of a right channel input signal Rin in response to a frequency of the right channel input signal Rin to thereby output a phase-changed right channel input signal;
first calculating means
11
a
for calculating a first difference between the left channel input signal Lin and the phase-changed right channel input signal outputted from the second all-pass filter lob to thereby output a first difference signal corresponding to the first difference as a left channel output signal Lout; and
second calculating means
11
b
for calculating a second difference between the right channel input signal Rin and the phase-changed left channel input signal outputted from the first all-pass filter
10
a
to thereby output a second difference signal corresponding to the second difference as a right channel output signal.
Each of the first all-pass filter
10
a
and the second all-pass filter may comprise by a first order all-pass filter. In general, this first order all-pass filter may not change the frequency characteristic of the input signal, but will change the phase characteristic thereof. For example, as indicated in
FIG. 2
, such a filter may be employed, by which the phase of the input signal is shifted by 180 degrees.
Each of the first calculating means
11
a
and the second calculating means
11
b
comprises, for example, an operational amplifier.
The first calculating means
11
a
subtracts the left channel input signal Lin from the phase-changed right channel input signal derived from the second all-pass filter
10
b
to obtain a first difference signal which is outputted as the left channel output signal Lout.
Similarly, the second calculating means
11
b
subtracts the right channel input signal Rin from the phase-changed left channel input signal derived from the first all-pass filter
10
a
to obtain a second difference signal which is outputted as the right channel output signal Rout.
Now, a consideration is made of such a case that both the first all-pass filter
10
a
and the second all-pass filter
10
b
are not employed. In this case, the first calculating means
11
a
subtracts the left channel input signal Lin from the right channel input signal Rin to obtain a difference signal, and then outputs this difference signal as the left channel output signal Lout. Similarly, the second calculating means
11
b
subtracts the rig
Fujita Akihiro
Kamada Kenji
Kuwano Kouji
Christie Parker & Hale LLP
Grier Laura A.
Harvey Minsun Oh
Kabushiki Kaisha Kawai Gakki Seisakusho
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