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JPS6398265

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DESCRIPTION JPS6398265
[0001]
[Summary] When voices recorded in stereo by two microphones are converted to digital signals
and the phase difference is determined, the higher power is used as the reference signal, and this
reference signal and the power of the smaller power signal By obtaining the phase difference, it
is possible to reduce the operation amount of phase difference detection and eliminate a fixed
delay in which one is always on the delay side. [Industrial field of application] In the present
invention, a voice conference system, a video conference system, etc. convert voices recorded in
stereo with two microphones into digital signals, obtain a phase difference, and encode them. The
present invention relates to improvement of a phase difference detection method for a
conference speech coding apparatus or the like, which is transmitted to the reception side with
voice and heard as a stereo signal on the reception side. As a phase difference detection method
for a conference speech coding apparatus or the like, it is desirable that the amount of
calculation of phase difference detection is small and it is not necessary to provide a fixed delay
in which one side is always on the delay side. [Prior Art] A conventional example will be
described below with reference to the drawings. FIG. 4 is a block diagram of a conventional
conference speech coding apparatus. In FIG. 4, voices recorded in stereo by two microphones 1
and 2 are converted to digital signals respectively by an analog-to-digital converter 3.4, and one
of them is input to the phase difference detector 8 with human power. And the other is input to
the phase difference detector 8 via the delay circuit 26 which gives a delay amount in the phase
difference detection range of the two digital signals in order to make the delay side always, and
the phase difference detector 8 The correlation function is calculated, and the maximum value of
the values is given (the phase difference is detected by setting the order as the signal amount
phase difference, and the detected difference is sent to the multiplexing unit 10. Also, the output
of the analog-to-digital converter 3.4 is added by the adder 25 to form a monaural signal, which
is encoded by the encoder 9 and sent to the multiplexing unit 10 as a low bit rate signal to be
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multiplexed and received Sending to the side. On the reception side, the signal encoded by the
separation unit 20 and the phase difference signal are separated, and the encoded signal is
decoded by the decoder 2I and branched, and one of the signals is delayed by the delay circuit
26. It is sent to the speaker 23 via the delay circuit 28 of the same delay amount as the amount,
and the other is given the delay amount of the phase difference signal sent by the variable phase
shifter 27 and sent to the speaker 24 to be a stereo signal. I am trying to The provision of the
delay circuit 26 in the above-described manner can be understood by the phase difference
detector 8 that which of the signal from the microphone 1 side and the signal from the
microphone 2 side is advanced in phase. Therefore, a delay circuit 26 for delaying the phase
difference detection range, which is the maximum phase difference for which the phase
difference can be obtained, is inserted in the microphone 2 side, and the signal on the
microphone 2 side is the microphone 1 The phase difference d = D + τ (τ may be advanced or
delayed due to the actual phase difference), which is a delay amount relative to the microphone 1
side, always delayed from the example signal. Ask and send it to the receiver.
On the reception side, assuming that the microphone 1 is on the right side and the microphone 2
is on the left side with respect to the sound source, the sound from the microphone l is heard
from the right speaker 23 and the sound from the microphone 2 is separated from the left
speaker 24 Need to For this purpose, the signal decoded by the decoder 21 is delayed by the
delay circuit 28 and sent to the right speaker 23 and the variable phase shifter 27 is delayed by
the phase difference d to the left. By sending to the speaker 24, the stereo sound can be
separated without making a mistake between right and left. [Problem to be Solved by the
Invention] However, in the above-mentioned phase difference detection method, it is not clear
either of the signal from the microphone 1 side and the signal from the microphone 2 side is in
advance although the phase is advanced. As to the voice that becomes the above, since the phase
difference detection range is shifted, as a result, it is necessary to perform an operation to detect
the phase difference twice as large as the phase difference detection range. There is a problem
that a delay circuit 26 is required to provide a delay of detection range. [Means for Solving the
Problems] As shown in FIG. 1, the above-mentioned problems are that the audio recorded in
stereo by two microphones 1.2 is digitalized by the analog / digital converter 3.4. Convert to
signals, calculate the power in power calculators 5 and 6, calculate the power level, compare in
level comparator 7, use selector 11 and use the higher level as the reference signal and lower the
level This is solved by the phase difference detection method of the present invention in which
the phase difference detector 8 inputs the signal as a sub signal to the phase difference detector
8 and finds the phase difference in which the sub signal lags the reference signal. [Operation]
Assuming that the distances between the seven sound sources 30 and the microphone 1 ° 2 are
a and b and a <b, as shown in FIG. 2, the level of the audio signal received by the microphone
31.32 is inversely proportional to the distance. The level of the microphone 1 is high, and the
phase difference is ((b−a) / sound velocity), and the microphone 2 is delayed. Therefore, the
present invention focuses on the point that the phase is always delayed from the high level one.
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That is, in the present invention, the outputs of the power calculation units 5 and 6 are compared
by the level comparator 7, and as a result, the higher one is used as the reference signal, and the
one whose phase lag is always lower is used as the auxiliary signal. At step S11, the signal is
switched and input to the phase difference detector 8, where a phase difference in which the sub
signal lags the reference signal is obtained. Therefore, the phase difference can be obtained in
the range of "D", the amount of calculation is reduced, and the delay circuit becomes
unnecessary.
An embodiment of the present invention will be described with reference to the drawings. FIG. 3
is a block diagram of a conference speech coding apparatus according to an embodiment of the
present invention. In FIG. 3, audio recorded in stereo by two microphones 1 and 2 is converted to
digital signals by analog / digital converters 3 and 4 respectively, and power is calculated by
power calculation unit 5.6. Then, the power level is determined and compared by the level
comparator 7 to determine which is higher. Assuming that the microphone 1 side on the right
side of the sound source is higher in level, a reference identification signal using the microphone
1 side as a reference signal is sent to the multiplexing unit 10 and the switches SWI and SW2 of
the selector are switched to solid lines. If the 2 side is high, the switch SW1. The signal of the
example of the microphone 1 is encoded by the encoder 9 and sent to the multiplexing unit 10.
Also, the higher level is used as a reference signal, and the lower level is input to the phase
difference detector 8 as a side signal, and the phase difference between the side signal and the
reference signal is determined by cross-correlation function calculation. It is sent to the
multiplexing unit 10, multiplexed with the reference identification signal and the encoded signal,
and sent to the receiving unit. On the receiving side, this is separated by the separation unit 20,
and the switch SW3. If SW4 is controlled to the solid line side and the level on the microphone 2
side is high, the switch SW3. SW4 is on the dotted line side, and the encoded signal on the right
side of the microphone 1, which is on the right side, is decoded by the decoder 21 and sent to the
speaker 23 on the right side. It is delayed and sent to the left speaker 24 and opened as a stereo
signal. In this case, since the calculation by the phase difference detector 8 is necessarily delayed
on the sub signal side, the range for detecting the phase difference is sufficient, and the amount
of calculation is smaller than in the prior art, and the delay side is known. There is no need for a
delay circuit that always takes the delay side. Therefore, when it is used for a speech encoding
apparatus for a conference, the delay on the transmitting side and the receiving side is almost
eliminated, and the stereo signal is not heard (it is not unpleasant for human beings. As described
above in detail, according to the present invention, the amount of operation for detecting the
phase difference by the phase difference detector is reduced, and a delay circuit which always
takes one as the delay side becomes unnecessary, and the voice code for the conference When
used in an audio system, there is almost no delay between the transmitting side and the receiving
side, and there is an effect that the person who listens to the stereo signal does not feel
uncomfortable.
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[0002]
Brief description of the drawings
[0003]
1 is a block diagram of the principle of the present invention, FIG. 2 is a diagram for explaining
the relationship between level and phase depending on the distance between a sound source and
a microphone, and FIG. 3 is a block diagram of a speech coding apparatus for conferencing
according to an embodiment of the present invention. FIG. 4 is a block diagram of a conventional
conference speech coding apparatus.
In the figure, ■, 2 is a microphone, 3.4 is an analog-to-digital converter, 5.6 is a power
calculator, 7 is a level comparator, 8 is a phase difference detector, 9 is an encoder, 10 is a
multiplexer , SWI and SW2 indicate switches.
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