JP2945570B2 - Signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ternary digital signal [+
[1, 0, -1], this signal is used as a control signal to set the conditions for applying a constant voltage to the voice coil of the speaker, that is, the polarity of the constant voltage and the ON / OFF conditions, and obtain a sound output by the speaker system. The present invention relates to a signal processing device .

[0002]

2. Description of the Related Art Conventionally, when a ternary digital signal is obtained by delta-sigma modulation of an input analog audio signal or digital audio signal in order to drive a speaker and output sound, setting a quantization threshold of a quantizer. Was fixed. That is, the full swing audio signal S
The range of (t) is [-1 <S (t) <1], and the signal input to the quantizer in the delta-sigma modulation circuit is X (t).
Then, for example, when X (t) ≦ − (）), the quantization value is “−1” − (１ ／) <X (t) <(１ ／), and the quantization value : “0” (１ ／) ≦ 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.

Here, as a general characteristic when a ternary digital signal is generated by performing delta-sigma modulation,
When the range to be quantized to “0” is expanded, that is, for example, the quantization threshold is set to [− (2/3), (2 /
3)], oscillation due to delta-sigma modulation is unlikely to occur even when an audio signal having a large peak value is input. Further, the level of quantization noise and the amount of harmonic distortion included in the generated ternary signal increase.

When the range to be quantized to "0" is narrowed, that is, for example, the quantization threshold is set to [-(1
/ 6), (1/6)], oscillation due to delta-sigma modulation easily occurs even when an audio signal having a large peak value is input. In addition, the level of the quantization noise included in the generated ternary signal decreases as compared with the case of (1). There is a tendency.

[0005]

However, in the above-mentioned conventional signal processing apparatus , when the ternary digital signal is generated, the quantization threshold is fixed in spite of the above-mentioned tendency, so that the oscillation limit is reduced. And the level of quantization noise are fixed. Therefore, the audio signal obtained after inputting the generated ternary digital signal to the low-pass filter and the generated ternary digital signal as a control signal are obtained by switching the voltage applied to the voice coil of the speaker. There is a problem that it is difficult to further expand the dynamic range of the acoustic signal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to make a quantization threshold variable when generating a ternary digital signal.
Expanding the dynamic range, avoiding oscillation phenomena and reducing quantization noise, can improve reproduction sound quality
It is to provide a signal processing device .

[0007]

In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that the ternary quantization means comprises two ternary quantization means after delta-sigma modulation of an input audio signal .
A ternary digital signal is generated by performing quantization using a quantization threshold, and generated by ternary quantization means.
Delta-valued audio signal
In a signal processing device for negatively feeding back to an input side at the time of sigma modulation, a peak value detecting means for detecting a peak value of an input audio signal, and the peak value information detected based on the peak value information detected by the peak value detecting means. while providing a threshold varying means for varying the quantization threshold value quantization means, the threshold value
When the peak value is larger than the set value,
Increase the interval of the quantization threshold, and the peak value is smaller than the set value.
Quantization threshold to narrow the interval between two quantization thresholds
Variable and the absolute value of the two quantization thresholds
It is characterized by making the values equal .

[0008] The invention according to claim 2 provides the signal according to claim 1.
The signal processing device is characterized in that a low-pass filter for demodulating the ternary digital signal generated by the ternary quantization means into an original audio signal is provided.

[0009] The invention according to claim 3 provides the communication according to claim 1.
The signal processing device is characterized in that a sound reproducing means for obtaining a sound signal by switching a voltage applied to a speaker based on the ternary digital signal generated by the ternary quantization means is provided.

[0010] The invention according to claim 4 is the invention according to claims 1 to
Item 3. In the signal processing device according to any one of Items 3, the threshold value varying means includes a peak value S of an input audio signal.
When (t) is in the range of -1 <S (t) <1, the quantization threshold is changed in the range of 0 <[absolute value of quantization threshold] <1. I have.

[0011]

According to the above arrangement, the input audio signal
When the peak value of the signal is detected by the peak value detecting means,
The threshold changing means determines that the detected peak value is larger than the set value.
Two quantizations in the ternary quantization means in critical cases
If the threshold interval is widened and it is smaller than the set value
Reduce the interval between two quantization thresholds in the ternary quantization means
The quantization threshold is varied so that two quantities
Input by equalizing the absolute value of the child threshold
Ternary quantization even when the peak value of the audio signal is large
By expanding the quantization range of "0" in the means
Oscillation in delta-sigma modulation circuit can be avoided
While the peak value of the input audio signal is small.
In this case, the quantization range of "0" in the ternary quantization means
The quantization noise level can be reduced by reducing the
You.

[0012]

Therefore, an audio signal obtained after inputting the generated ternary digital signal to the low-pass filter and an audio signal obtained by switching the voltage applied to the speaker using the generated ternary digital signal as a control signal. Since the dynamic range of the signal is expanded, the quality of reproduced sound 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 have a large ratio of the peak value of the audio signal to the switching voltage, so that good and efficiency can be obtained. Good sound reproduction becomes possible.

That is, by making the quantization threshold variable when generating a ternary digital signal, the dynamic range is expanded, the oscillation phenomenon is avoided, the quantization noise is reduced, and the reproduction sound quality is improved. be able to.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the speaker driving device of the present embodiment to which the signal processing device of the present invention is applied has an input terminal 1 for inputting an analog audio signal or a digital audio signal. 1 is connected to a delta-sigma modulation circuit 2, and the output of the delta-sigma modulation circuit 2 is input to a switching drive speaker 4 via a switching circuit 3.

The delta-sigma modulation circuit 2 includes integrators 6 for performing delta-sigma modulation on the audio signal.
A multiplier 7, an adder 8, a one-clock delay unit 9, and the like are connected, and a quantizer 10 as ternary quantization means for generating a ternary digital signal is provided.

A peak value detecting circuit 5 is connected to the input terminal 1, and the output of the peak value detecting circuit 5 is transmitted through a threshold value changing device 11 as a threshold value changing means composed of a microcomputer chip or the like. And input to the quantizer 10.

That is, when the peak value of the audio signal input by the peak value detection circuit 5 is larger than the set value, the threshold value varying device 11 sets the quantization range of “0” in the quantizer 10 to the threshold value. On the other hand, when the peak 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.

On the other hand, the switching circuit 3 includes the quantizer 1
When the output of 0 is "+1", a constant voltage in the positive direction is applied to a voice coil (not shown) of the switching drive speaker 4, and when the output of the quantizer 10 is "0", the switching drive speaker 4 The voltage application to the voice coil is turned off, and when the output of the quantizer 10 is “−1”, a constant negative voltage is applied to the voice coil of the switching speaker 4.

The operation of the speaker driving device having the above configuration will be described. First, the audio signal input to the input terminal 1 is input to a peak value detection circuit 5, and the peak value detection circuit 5 detects the absolute value of the input signal peak value. However, the peak value S (t) of the input audio signal is in the range of -1 <S (t) <1.

On the other hand, the audio signal input to the delta-sigma modulation circuit 2 is guided to an integration loop composed of multi-stage integrators 6 and then added by an adder 8.
The value is input to a quantizer 10. In this quantizer 10, for example, [-(1/3), + (1/3)]
The absolute values of the two quantization thresholds are set to be equal, and the quantizer 10 is determined by these two quantization thresholds.
If the added result is larger than two quantization thresholds, the quantization value = “+ 1”. If the added result is between the two quantization thresholds, the quantization value = “0”. Is smaller than the two quantization thresholds, the quantization value = “− 1” is output. Further, the two quantization thresholds can be changed in the range of 0 <[absolute value of the quantization threshold] <1 by the threshold variable device 11, and the threshold variable device 11 If the crest value information is larger than the set value based on the crest value information, the absolute value of the quantization threshold is set to be larger, and if the crest value information is smaller than the set value, the quantization threshold is set. Is continuously controlled so that the absolute value of is set smaller.

This will be described in detail with reference to FIGS. 2 (a), 2 (b) and 2 (c). That is, as shown in FIG.
When a sine wave of z is input, | quantization threshold | = 1 /
In the case of 3, the position indicated by the broken line is the oscillation limit, and the portion indicated by the diagonal lines is the existence range of the audio output signal.

Now, for this sine wave, | quantization threshold |
Assuming that ＝= 2/3, as shown in FIG. 2B, the oscillation limit rises to the position indicated by the broken line in FIG. 2B, and the peak value also rises, so that delta-sigma modulation of a large peak value is possible. Becomes However, at this time, the quantization noise level also increases.

On the other hand, as shown in FIG. 2 (c), if | quantization threshold | = 1/6 with respect to the sine wave, the oscillation limit is lowered to the position indicated by the broken line in FIG. At the same time as the peak value falls, the quantization noise level also falls. Therefore, it is possible to reproduce even a signal having a small peak value after the delta-sigma modulation.

As described above, when the quantization threshold is changed in accordance with the input peak value, the level of the quantization noise changes. Therefore, the maximum signal and the minimum signal (which cannot be buried in the quantization noise) by delta-sigma modulation. (Minimum signal) can be made larger than before. Therefore, the dynamic range is expanded in this sense.

The output of the quantizer 10 on which the above processing has been performed is negatively fed back to the input section of the delta-sigma modulation circuit 2 via a one-clock delay unit 9 and the like, and a control signal for controlling the switching circuit 3. Is output as Then, the switching circuit 3 sets the output of the quantizer 10 to “+”.
In the case of "1", a constant voltage in the positive direction is applied to the switching drive speaker 4, and when the output of the quantizer 10 is "+1", the voltage application to the switching drive speaker 4 is turned off. When the output of the switch 10 is “−1”, the switching is performed so that a constant negative voltage is applied to the switching drive speaker 4.

The switching voltage is output to a voice coil (not shown) of the switching speaker 4 to reproduce sound.

As described above, in the speaker drive device of the present embodiment, the peak value of the input audio signal is detected by the peak value detecting circuit 5. Then, the threshold variable device 11
When the peak value of the audio signal input by the peak value detection circuit 5 is larger than the set value, the quantization range of “0” in the quantizer 10 is expanded, while the peak value of the input audio signal is set. If the value is smaller than the value, the quantization threshold is changed so as to narrow the quantization range of “0” in the quantizer 10.

As a result, even when the peak value of the input audio signal is large, the quantization range of “0” in the quantizer 10 is expanded to thereby increase the delta-sigma modulation circuit 2.
Can be avoided, but when the peak value of the input audio signal is small, the annoying quantization noise level can be reduced by narrowing the quantization range of “0” in the quantizer 10. .

Therefore, the voltage applied to the switching drive speaker 4 is switched using the audio signal obtained after inputting the generated ternary digital signal to a low-pass filter (not shown) and the generated ternary digital signal as control signals. As a result, the dynamic range of the acoustic signal obtained is expanded, so that the switching drive speaker 4 can realize audio reproduction with a wide dynamic range, and can improve reproduction sound quality.

That is, by making the quantization threshold for generating a ternary digital signal variable with a simple circuit configuration, the dynamic range can be expanded, oscillation phenomena can be avoided, and quantization noise can be reduced, and reproduction can be performed. Sound quality can be improved.

In particular, the acoustic signal obtained by switching the voltage applied to the switching drive speaker 4 using the generated ternary digital signal as a control signal is:
Since the ratio of the peak value of the audio signal to the switching voltage can be increased, sound reproduction can be performed well and efficiently. For example, + 5V, 0V,
When three values of -5 V are switched at a high speed with a signal after delta-sigma modulation, the maximum peak value of an audio band signal that can be extracted from this switching signal can be made larger than before. That is, for example, if the switching maximum potential difference is 10 V, the maximum peak value of the conventional audio band signal is 4 Vpp, but in the present embodiment, it is 8 Vpp, for example. Therefore, since an audio signal having a higher peak value than that of the related art can be obtained from the same power supply voltage, efficient sound reproduction becomes possible.

In this embodiment, a method has been described in which a ternary digital signal is directly input to the switching circuit 3 as a control signal for switching the voltage applied to the switching drive speaker 4. However, the present invention is not limited to this. For example, the same effect can be obtained 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.

[0035]

As described above, the signal processing device according to the first aspect of the present invention converts an input audio signal into a delta signal.
After the sigma modulation, the ternary quantization means sets two quantization thresholds.
A ternary digital signal is obtained by performing quantization using values.
And the 3 generated by the ternary quantization means.
Value digital signal, audio signal delta-sigma
Signal processing device that provides negative feedback to the input side when tuning
A peak value detecting means for detecting a peak value of an input audio signal; and a threshold value varying means for varying a quantization threshold value of the ternary quantizing means based on the peak value information detected by the peak value detecting means. While the threshold variable means
Are two quantization thresholds when the peak value is greater than the set value.
When the value interval is widened and the peak value is smaller than the set value
Variable quantization threshold to narrow the interval between two quantization thresholds
And at that time, the absolute values of the two quantization thresholds are equal
It is a Kusuru configuration.

The invention according to claim 2 is the same as the invention according to claim 1.
In the signal processing device described above, the ternary quantization means
The ternary digital signal generated by
This is a configuration in which a low-pass filter for demodulating is provided.

The invention according to claim 3 is the same as the invention according to claim 1.
In the signal processing device described above, the ternary quantization means
To the speaker based on the ternary digital signal generated by
Reproduction to obtain sound signal by switching applied voltage
This is a configuration in which means are provided.

The invention described in claim 4 is the same as the invention described in claim 1.
4. The signal processing device according to claim 3, wherein
The threshold variable means is used to calculate the peak value of the input audio signal.
When S (t) is in the range of -1 <S (t) <1, the quantity
The quantization threshold in the range of 0 <[absolute value of quantization threshold] <1
It is configured to change.

Thus, even when the peak value of the input audio signal is large, it is possible to avoid oscillation in the delta-sigma modulation circuit by expanding the quantization range of "0" in the ternary quantization means. on the other hand,
If the peak value of the input audio signal is small, 3
The quantization noise level can be reduced by narrowing the quantization range of "0" in the value quantization means.

Therefore, an audio signal obtained by inputting the generated ternary digital signal to the low-pass filter and an acoustic signal obtained by switching the voltage applied to the speaker using the generated ternary digital signal as a control signal. Since the dynamic range of the signal is expanded, the quality of reproduced sound 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 have a large ratio of the peak value of the audio signal to the switching voltage, so that good and efficiency can be obtained. Good sound reproduction becomes possible.

That is, by making the quantization threshold variable when generating a ternary digital signal, the dynamic range can be expanded, the oscillation phenomenon and the quantization noise can be reduced, and the reproduced sound quality can be improved. This has the effect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a speaker driving device according to an embodiment of the present invention.

FIGS. 2A and 2B are explanatory diagrams showing a spectrum level of an audio output signal. FIG. 2A shows a case where | quantization threshold | = 1/3, FIG. 2B shows a case where | quantization threshold | = 2/3, c) shows the case where | quantization threshold | = 1/6.

[Explanation of symbols]

 Reference Signs List 2 Delta-sigma modulation circuit 3 Switching circuit 4 Switching drive speaker (speaker) 5 Peak value detection circuit (peak value detection means) 10 Quantizer (ternary quantization means) 11 Threshold variable device (threshold variable means)

Claims (4)

(57) [Claims] 1. A ternary quantizer uses two quantization thresholds after delta-sigma modulation of an input audio signal .
To generate a ternary digital signal by performing quantization, and the ternary digital signal generated by the ternary quantization means.
Digital signal, delta-sigma modulation of audio signal
A signal processing device for providing a negative feedback to the input side at the time, a peak value detecting means for detecting a peak value of the input audio signal, and the ternary quantization based on the peak value information detected by the peak value detecting means. A threshold variable means for varying a quantization threshold of the means, while the threshold variable means is provided when the peak value is larger than a set value.
Widen the interval between the two quantization thresholds and make the peak value
To narrow the interval between two quantization thresholds when
The quantization threshold is varied, and two quantization thresholds are used.
A signal processing device for making the absolute values of the values equal . 2. The three-value quantization means according to claim 2, wherein
2. The signal processing apparatus according to claim 1, further comprising a low-pass filter for demodulating the value digital signal into an original audio signal. 3. The three-valued quantizer generated by the ternary quantizer.
2. The signal processing apparatus according to claim 1, further comprising: a sound reproducing unit that switches an applied voltage to the speaker based on the digital value signal to obtain a sound signal. 4. The threshold changing means sets a quantization threshold to 0 <[quantization when a peak value S (t) of an input audio signal is in a range of -1 <S (t) <1. 4. The signal processing apparatus according to claim 1, wherein the absolute value of the threshold value is changed within a range of <1.