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DESCRIPTION JPH07131881

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DESCRIPTION JPH07131881
[0001]
BACKGROUND OF THE INVENTION The present invention delta sigma modulates an input audio
signal into a ternary digital signal [+1, 0, -1], and then uses this signal as a control signal to
control the voice coil of the speaker. The present invention relates to a speaker driving device
that sets a constant voltage application condition, that is, a constant voltage polarity and an ON /
OFF condition, and obtains an acoustic output from a speaker system.
[0002]
2. Description of the Related Art Conventionally, in the case where delta sigma modulation of an
input analog audio signal or digital audio signal is performed to obtain a ternary digital signal in
order to drive a speaker for sound output, setting of a quantization threshold of a quantizer is
performed. Was fixed. That is, assuming that the range of the full swing audio signal S (t) is [−1
<S (t) <1] and the signal input to the quantizer in the delta sigma modulation circuit is X (t), for
example, , X (t) ≦ − (1/3), the quantization value: “−1” − (1/3) <X (t) <(1/3), the
quantization value: “0” In the case of (1/3) ≦ X (t), the quantization value is “+1”. The
quantization threshold at this time is [− (1/3), (1/3)], and these values are fixed regardless of the
peak value of the input audio signal.
[0003]
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Here, as a general characteristic when delta sigma modulation is performed to generate a ternary
digital signal, when the range to be quantized to "0" is expanded, that is, for example, the
quantization threshold is In the case of (2/3), (2/3)], even if an audio signal having a large peak
value is input, oscillation due to delta sigma modulation hardly occurs. Also, the level of
quantization noise and the amount of harmonic distortion included in the generated ternary
signal increase.
[0004]
When the range to be quantized to "0" is narrowed, that is, for example, when the quantization
threshold is [-(1/6), (1/6)] under the above conditions, an audio signal with a large peak value
Even when is input, oscillation due to delta sigma modulation tends to occur. Also, the level of
quantization noise included in the generated ternary signal is reduced compared to the case of.
There is a tendency.
[0005]
However, in the above-described conventional speaker driving device, the quantization threshold
is fixed despite the above tendency when generating a ternary digital signal, so the oscillation
limit is generated. And the level of quantization noise is fixed. For this reason, it is obtained by
switching the voltage applied to the voice coil of the speaker by using the audio signal obtained
after inputting the generated ternary digital signal to the low pass filter and the generated
ternary digital signal as the control signal. There is a problem that it is difficult to further expand
the dynamic range of the acoustic signal.
[0006]
The present invention has been made in view of the above-mentioned conventional problems,
and its object is to expand the dynamic range and make the oscillation phenomenon by changing
the quantization threshold when generating a ternary digital signal. It is an object of the present
invention to provide a speaker driving device which can improve the reproduction sound quality
by avoiding quantization noise and reducing quantization noise.
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the speaker
driving device of the present invention delta sigma modulates an input audio signal to generate a
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ternary digital signal by ternary quantization means, In the speaker driving device for switching
the voltage applied to the speaker based on the control signal to reproduce the sound, the peak
value detecting means for detecting the peak value of the input audio signal and the detected
peak value information 3 It is characterized in that threshold value variable means for changing
the quantization threshold value of the value quantization means is provided.
[0008]
According to the above configuration, the peak value of the audio signal inputted by the peak
value detecting means is detected.
Then, when the crest value of the audio signal input by the crest value detection means is larger
than the set value by the threshold value changing means, the quantization range of “0” in the
ternary quantization means is expanded while being inputted When the crest value of the audio
signal is smaller than the set value, it is possible to change the quantization threshold so as to
narrow the quantization range of "0" in the ternary quantization means.
[0009]
As a result, even when the crest value of the input audio signal is large, it is possible to avoid the
oscillation in the delta sigma modulation circuit by widening the quantization range of "0" in the
ternary quantization means, while the input When the peak value of the audio signal to be
reproduced is small, the quantization noise level can be reduced by narrowing the quantization
range of "0" in the ternary quantization means.
[0010]
Therefore, the dynamic of the audio signal obtained after inputting the generated ternary digital
signal into the low pass filter, and the dynamic of the acoustic signal obtained by switching the
voltage applied to the speaker using the generated ternary digital signal as the control signal.
Since the range is expanded, the reproduction sound quality can be improved.
In particular, an acoustic signal obtained by switching a voltage applied to a speaker using the
generated ternary digital signal as a control signal can increase the ratio of the peak value of the
audio signal to the switching voltage, so that it is good and efficient. Good sound reproduction is
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possible.
[0011]
That is, by making the quantization threshold value variable at the time of generating the ternary
digital signal, the dynamic range can be expanded, the oscillation phenomenon can be avoided,
and the quantization noise can be reduced to improve the reproduction sound quality. .
[0012]
DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description will explain one
embodiment of the present invention in reference to FIG. 1 and FIG.
[0013]
As shown in FIG. 1, the speaker driving apparatus of this embodiment has an input terminal 1 to
which an analog audio signal or a digital audio signal is input, and a delta sigma modulation
circuit 2 is connected to the input terminal 1. The output of the delta sigma modulation circuit 2
is input to the switching drive speaker 4 via the switching circuit 3.
[0014]
The above-described delta sigma modulation circuit 2 is connected to an integrator 6..., A
multiplier 7..., An adder 8 and a 1 clock delay 9 etc. for delta sigma modulating an audio signal,
and a ternary digital A quantizer 10 is provided as ternary quantization means for generating a
signal.
[0015]
A peak value detection circuit 5 is connected to the input terminal 1, and the output of the peak
value detection circuit 5 is quantized through a threshold value variable device 11 as threshold
value variable means such as a microcomputer chip, for example. It is designed to be input to the
unit 10.
[0016]
That is, when the crest value of the audio signal input by the crest value detection circuit 5 is
larger than the set value, the above-described threshold variable device 11 widens the
quantization range of “0” in the quantizer 10; When the crest value of the input audio signal is
smaller than the set value, the quantization threshold is changed so as to narrow the quantization
range of “0” in the quantizer 10.
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[0017]
On the other hand, when the output of the quantizer 10 is "+1", the switching circuit 3 applies a
constant voltage in the positive direction to the voice coil (not shown) of the switching drive
speaker 4 and the output of the quantizer 10 is "0". In the case, the voltage application to the
voice coil of the switching drive speaker 4 is turned off, and when the output of the quantizer 10
is “−1”, a constant voltage in the negative direction with respect to the voice coil of the
switching drive speaker 4 Is to be applied.
[0018]
The operation of the speaker driving device having the above configuration will be described.
First, an audio signal input to the input terminal 1 is input to the peak value detection circuit 5,
and the peak value detection circuit 5 detects the absolute value of the input signal peak value.
However, it is assumed that the peak value S (t) of the input audio signal is in the range of −1 <S
(t) <1.
[0019]
On the other hand, the audio signal input to the delta sigma modulation circuit 2 is led to an
integration loop composed of multistage integrators 6, then added by the adder 8 and then input
to the ternary quantizer 10. .
In this quantizer 10, for example, the absolute values of the two quantization thresholds are set
to be equal as in [− (1/3), + (1/3)], and these two quantization thresholds are set. The quantizer
10 determines that the quantization value = “0” if the quantization value = “+ 1” is between
the two quantization thresholds if the sum is greater than the two quantization thresholds. If the
result of the addition is smaller than two quantization thresholds, it outputs a ternary value of
quantization value = "-1".
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Further, the two quantization thresholds can be changed by the threshold variable device 11 in
the range of 0 <[absolute value of quantization threshold] <1, and the threshold variable device
11 receives the peak value detection circuit 3 The absolute value of the quantization threshold is
set larger if the peak value information is larger than the set value based on the peak value
information of the quantization threshold, and the quantization threshold is set if the peak value
information is smaller than the set value It controls continuously to set the absolute value of to a
smaller value.
[0020]
This will be described in detail based on FIGS. 2 (a), (b) and (c).
That is, as shown in FIG. 2A, when a 1 kHz sine wave is input, the position shown by the broken
line is the oscillation limit when | quantization threshold | = 1⁄3; The hatched portion is the range
of the audio output signal.
[0021]
Now, assuming that | quantization threshold | = 2/3 with respect to this sine wave, as shown in
FIG. 2B, the oscillation limit rises to the position of the broken line shown in the figure, whereby
the peak value is also As it rises, delta sigma modulation of a large peak value becomes possible.
At the same time, however, the quantization noise level also rises.
[0022]
On the other hand, as shown in FIG. 2 (c), assuming that | quantization threshold | = 1/6 with
respect to the above-mentioned sine wave, the oscillation limit falls to the position of the broken
line shown in FIG. At the same time as falling, the quantization noise level also falls.
Therefore, even after a signal with a small peak value, reproduction after delta sigma modulation
becomes possible.
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[0023]
In this way, when the quantization threshold is changed according to the input peak value, the
level of quantization noise changes, so the maximum signal and the minimum signal (the
minimum signal not buried in quantization noise) by delta sigma modulation The difference with)
can be taken larger than before.
Therefore, the dynamic range is expanded in this sense.
[0024]
The output of the quantizer 10 subjected to the above-described processing is negatively fed
back to the input portion of the delta sigma modulation circuit 2 via a one-clock delay 9 or the
like, and is output as a control signal for controlling the switching circuit 3 Ru. Then, the
switching circuit 3 applies a constant voltage in the positive direction to the switching drive
speaker 4 when the output of the quantizer 10 is “+1”, and when the output of the quantizer
10 is “+1”. When the voltage application is turned off for the switching drive speaker 4 and
the output of the quantizer 10 is “−1”, the switching drive speaker 4 is switched to apply a
constant voltage in the negative direction.
[0025]
Then, the switching voltage is output to the voice coil (not shown) of the switching drive speaker
4 to reproduce the sound.
[0026]
As described above, in the speaker driving device according to the present embodiment, the peak
value of the audio signal input in the peak value detection circuit 5 is detected.
Then, when the crest value of the audio signal input by the crest value detection circuit 5 is
larger than the set value, the threshold variable device 11 widens the quantization range of
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“0” in the quantizer 10 while being inputted. If the crest value of the audio signal is smaller
than the set value, the quantization threshold is changed so as to narrow the quantization range
of “0” in the quantizer 10.
[0027]
As a result, even when the crest value of the input audio signal is large, it is possible to avoid the
oscillation in the delta sigma modulation circuit 2 by widening the quantization range of “0” in
the quantizer 10, If the peak value of the audio signal to be played back is small, it is possible to
reduce the offensive quantization noise level by narrowing the quantization range of "0" in the
quantizer 10.
[0028]
Therefore, it is obtained by switching the voltage applied to the switching drive speaker 4 by
using the audio signal obtained after inputting the generated ternary digital signal to the low
pass filter (not shown) and the generated ternary digital signal as the control signal. Since the
dynamic range of the audio signal to be output is expanded, the switching drive speaker 4 can
realize audio reproduction with a wide dynamic range, and can improve the reproduction sound
quality.
[0029]
That is, by making the quantization threshold variable at the time of generating a ternary digital
signal variable by a simple circuit configuration, the dynamic range is expanded, the oscillation
phenomenon is avoided, and the quantization noise is reduced to improve the reproduction
sound quality Can be
[0030]
In particular, an acoustic signal obtained by switching a voltage applied to the switching drive
speaker 4 using the generated ternary digital signal as a control signal can increase the ratio of
the peak value of the audio signal to the switching voltage, Good and efficient sound
reproduction is possible.
For example, when three values of +5 V, 0 V and -5 V are switched at high speed with a signal
after delta sigma modulation, the maximum peak value of the audio band signal that can be
extracted from this switching signal can be made larger than before.
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That is, for example, assuming that the switching maximum potential difference is 10 V, the
maximum peak value of the conventional audio band signal is 4 Vpp, but in this embodiment it is
8 Vpp, for example.
Therefore, since an audio signal having a peak value larger than that of the conventional one can
be obtained from the same power supply voltage, efficient acoustic reproduction can be
performed.
[0031]
In the present embodiment, the method of directly inputting the ternary digital signal to the
switching circuit 3 as the control signal for switching the voltage applied to the switching drive
speaker 4 has been described. However, the present invention is not limited thereto. The same
effect can be obtained even when an audio signal is obtained by inputting a ternary digital signal
to a general low-pass filter. In this case, the output of the low pass filter is acoustically
reproduced from the speaker via the amplifier.
[0032]
As described above, according to the speaker driving device of the present invention, the peak
value detecting means for detecting the peak value of the input audio signal and the ternary
quantization means based on the detected peak value information. And threshold value variable
means for changing the quantization threshold value of.
[0033]
As a result, even when the crest value of the input audio signal is large, it is possible to avoid
oscillation in the delta sigma modulation circuit by widening the quantization range of “0” in
the three-value quantization means, When the peak value of the audio signal to be reproduced is
small, the quantization noise level can be reduced by narrowing the quantization range of "0" in
the ternary quantization means.
[0034]
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Therefore, the dynamic of the audio signal obtained after inputting the generated ternary digital
signal into the low pass filter, and the dynamic of the acoustic signal obtained by switching the
voltage applied to the speaker using the generated ternary digital signal as the control signal.
Since the range is expanded, the reproduction sound quality can be improved.
In particular, an acoustic signal obtained by switching a voltage applied to a speaker using the
generated ternary digital signal as a control signal can increase the ratio of the peak value of the
audio signal to the switching voltage, so that it is good and efficient. Good sound reproduction is
possible.
[0035]
That is, by making the quantization threshold value variable at the time of generating the ternary
digital signal, the dynamic range can be expanded, the oscillation phenomenon and the
quantization noise can be reduced, and the reproduction sound quality can be improved. Play.
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