JP2007028329A - Muting apparatus, digital audio apparatus and muting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of shock-noise during the time-constant muting. <P>SOLUTION: The time-constant muting unit 11 as a muting means applies muting by gradually reducing a muting gain to an input signal. A muting control unit 22 as an adjusting means adjusts a reducing rate of the muting gain by the time-constant muting unit 11 in accordance with a gain setting value of a volume control 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a muting device, a digital audio device, and a muting method.

  Conventionally, a circuit that performs muting by multiplying a digital signal by a coefficient and gradually reducing the coefficient has been proposed (see, for example, Patent Document 1). Hereinafter, the method of applying mute by gradually decreasing the mute gain is referred to as time constant mute. Such a time constant mute is usually used to reduce noise generated due to a steep voltage change at the time of normal mute in which sound is stopped instantaneously.

  FIG. 7 is a diagram illustrating an example of a signal when time constant mute is applied. In FIG. 7, a solid line represents a signal, and a broken line represents a mute gain. As shown in FIG. 7, when the time constant mute is applied, the mute gain is gradually decreased from the start time To, and the mute gain becomes zero at the end time Te.

  When the time constant mute is realized by a DSP (digital signal processor) or the like, the mute gain is lowered by one mute step every sampling period, thereby realizing the time constant mute. FIG. 8 is an enlarged view of a broken line circle portion of FIG. As shown in FIG. 8, at the time constant mute, the mute gain is microscopically reduced stepwise.

  In the case of a digital audio device, a volume is often arranged at a subsequent stage from a circuit that performs such mute.

  FIG. 9 is a block diagram showing a configuration of a conventional digital audio apparatus. As shown in FIG. 9, when the volume circuit 102 exists in the subsequent stage of the DSP 101 having the time constant mute unit 111 for performing the time constant mute in the audio signal path, the volume circuit 102 is a user for a volume operation unit (not shown). In accordance with the operation, the volume of the audio signal is adjusted with the volume gain, and thus the volume.

  Normally, the volume gain of the volume circuit 102 is 0 or more and 1 or less, and the audio signal is attenuated. However, since the audio signal is amplified by the amplifier circuit 103 in the subsequent stage, it is supplied to an audio output device such as a speaker or headphones. The amplitude of the audio signal is larger than the amplitude of the audio signal output from the volume circuit 102.

  When the volume gain of the volume circuit 102 is large, the amplitude of the audio signal supplied to the audio output device such as a speaker or a headphone increases. When the volume gain is small, the amplitude of the audio signal supplied to the audio output device. Becomes smaller.

JP 2001-203581 A (summary etc.)

  When the volume circuit 102 and the amplifier circuit 103 exist after the time constant mute unit 111 as in the conventional audio device, the amplitude of the audio signal supplied to the audio output device is large when the volume gain of the volume circuit 102 is large. Therefore, if time constant mute is applied when the volume gain is large, the rate of decrease in volume (attenuation amount at a certain time) due to mute for the audio signal supplied to the audio output device is It becomes larger than the decrease rate of mute gain.

  That is, when the time constant mute is applied when the volume gain is large, the mute step on the audio signal supplied to the audio output device is larger than when the time constant mute is applied when the volume gain is small.

  FIG. 10 is a diagram for explaining time constant mute when the volume gain is large. 10A illustrates an example of an audio signal output from the DSP 101, and FIG. 10B illustrates an example of an audio signal supplied to the audio output device. Note that the audio signal output from the DSP 101 is a digital signal, but for the sake of explanation, it is drawn in an analog manner in FIG. As the volume gain of the volume circuit 102 is larger, as shown in FIG. 10B, the mute step on the audio signal supplied to the audio output device becomes larger.

  Therefore, when the volume gain is large, when the mute gain is decreased by the mute step, a sharp voltage change occurs in the audio signal supplied to the audio output device, and the audio signal is mixed with the audio from the audio output device. Shock noise becomes noticeable.

  Also, since the user tends to listen to the sound at a substantially constant volume for each environment, the volume value is set to be large when the input signal level is originally low, and the volume value is set to be high when the input signal level is originally high. It tends to be set smaller. Therefore, the volume value tends to be set larger as the input signal level is smaller.

  For this reason, in a situation where the level of the input signal is generally low and the volume value is set to be high, the level of shock noise with respect to the audio signal is relatively large in the conventional apparatus, and the shock noise is easily noticeable.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain a muting device, a digital audio device, and a muting method that can suppress the generation of shock noise during time constant muting.

  In order to solve the above problems, the present invention is configured as follows.

  The muting device according to the present invention includes a muting means for gradually muting the mute gain with respect to the input signal, and an adjustment for adjusting a decrease speed of the mute gain by the muting means in accordance with a gain setting value of the volume. Means.

  The muting device according to the present invention may be as follows in addition to the above muting device. In other words, in this case, the adjusting means slows down the mute gain decreasing rate as the volume setting value is larger.

  A digital audio apparatus according to the present invention includes a digital signal processor that reduces the mute gain by a mute step at regular intervals, and multiplies the audio signal by the mute gain, and an amplitude of the audio signal that is positioned before or after the digital signal processor. And a control circuit for setting the mute step of the digital signal processor in accordance with the volume gain of the volume.

  In addition to the above digital audio device, the digital audio device according to the present invention may be configured as follows. That is, in that case, the control circuit sets the mute step to a smaller value as the volume gain of the volume is larger.

  The digital audio apparatus according to the present invention may be as follows in addition to any of the above digital audio apparatuses. That is, in this case, the control circuit sets the volume gain of the volume, and when the volume gain of the volume is changed, specifies the mute step value according to the changed volume gain, and uses that value for the digital signal processor. Update the mute step value.

  The muting method according to the present invention includes a step of setting a mute gain decrease rate according to a volume gain setting value, and a mute gain for the input signal gradually decreasing at the set mute gain decrease rate. The step of applying.

  ADVANTAGE OF THE INVENTION According to this invention, the muting apparatus, digital audio apparatus, and muting method which can suppress generation | occurrence | production of the shock noise at the time of a time constant mute can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of the digital audio apparatus according to Embodiment 1 of the present invention. In FIG. 1, a digital signal processor (DSP) 1 is a circuit that performs predetermined processing on a digital input signal. In the DSP 1, the time constant mute unit 11 is a part that functions as a muting unit that performs mute by gradually decreasing the mute gain multiplied to the digital input signal during the mute operation. The time constant mute unit 11 of the DSP 1 reduces the mute gain by a mute step every fixed period such as a sampling period or a constant multiple thereof.

  The volume circuit 2 is an electronic volume circuit that is positioned after the DSP 1 and adjusts the amplitude of the audio signal in accordance with the volume setting value. The volume circuit 2 reduces the amplitude (digital value) of the digital signal and outputs it.

  The control circuit 4 is a circuit that controls the DSP 1 and the volume circuit 2 by supplying data and control signals to the DSP 1 and the volume circuit 2. The control circuit 4 is configured by, for example, a program stored in a recording medium such as a microprocessor, for example, a ROM, and executed by the microprocessor.

  In the control circuit 4, the volume control unit 21 is a part having a function of setting data specifying a volume gain for the volume circuit 2. The mute control unit 22 is a part for setting data specifying the mute gain reduction rate for the time constant mute unit 11. Further, the mute control unit 22 functions as an adjustment unit that adjusts the value of data that specifies the decrease rate of the mute gain in accordance with the value of data set in the volume circuit 2 by the volume control unit 21. The mute controller 22 of the control circuit 4 sets a mute step in the DSP 1 according to the volume setting value of the volume circuit 2.

  The time constant mute unit 11 and the mute control unit 22 constitute an embodiment of a muting device.

  Next, the operation of the above apparatus will be described.

  For example, when a volume operation unit (not shown) is operated, the volume control unit 21 of the control circuit 4 detects this, and sets data specifying a volume gain in the volume circuit 2 in accordance with the operation.

  Then, the mute control unit 22 of the control circuit 4 sets a data value that specifies the decrease rate of the mute gain in accordance with the data value corresponding to the volume gain set in the volume circuit 2 (hereinafter referred to as volume value). decide. When the volume gain of the volume circuit 2 is changed by the volume control unit 21, the mute control unit 22 of the control circuit 4 specifies the value of the mute step according to the changed volume gain, and the DSP 1 The value of the mute step in the time constant mute unit 11 is updated.

  In the first embodiment, a mute step indicating the amount of decrease in mute gain for each sampling period is used as data specifying the mute gain decrease rate. FIG. 2 is a diagram illustrating an example of a correspondence relationship between a volume value and a mute step value according to the first embodiment. As shown in FIG. 2, when the volume value is large, the mute step value is set small. That is, when the volume gain of the volume circuit 2 is large, the decrease rate of the mute gain at the time of mute becomes slow.

  The correspondence between the two shown in FIG. 2 is linear. In FIG. 2, when the volume value is the minimum value Vmin, the mute step is set to the maximum value MSmax, and when the volume value is the maximum value Vmax, the mute step is set to the minimum value MSmin.

  The mute step MS in this case is calculated by the mute controller 22 based on the volume value VS of the volume circuit 2 according to the equation (1). The volume value is also referred to as a volume step when the volume value is set discretely.

  MS = MS0−VS × ΔMS (1)

  Here, MS0 is a default value of the mute step MS, and ΔMS is a change amount of the mute step MS per unit of volume value (one volume step).

  FIG. 3 is a diagram showing a specific example of the correspondence relationship between the volume value and the mute step value in the first embodiment. The example shown in FIG. 3 is an example when VS is an integer value of 0 to 35, MS0 = 0.1, and ΔMS = 0.001 in Formula (1). In this example, the volume value is one of 36 levels, and when the volume value is “0” (that is, when the volume gain is −∞ decibels), the mute step is set to 0.1. When the volume value is “35” (that is, the volume gain is 0 dB), the mute step is set to 0.065. In this example, every time the volume value decreases by “1”, the value of the mute step decreases by “0.001”.

  The mute controller 22 may calculate the mute step value according to the equation (1), or store a table as shown in FIG. 3 in advance and determine the mute step value by referring to the table. You may do it.

  Then, the mute controller 22 of the control circuit 4 sets the mute step value thus obtained in the time constant mute unit 11 of the DSP 1.

  Here, the operation at the time constant mute will be described.

  For example, when a user operation on an operation unit such as a mute switch (not shown) is detected, the mute control unit 22 of the control circuit 4 causes the time constant mute unit 11 to execute time constant mute.

  When the time constant mute unit 11 of the DSP 1 receives a time constant mute start command from the mute control unit 22, the time constant mute unit 11 executes the time constant mute with the value of the mute step MS supplied by the mute control unit 22.

  When the value of the input signal at time n is IN (n) and the mute gain at time n is G (n), the value OUT (n) of the output signal from the time constant mute unit 11 at time n is Calculated by the time constant mute unit 11 according to the equation (2).

  OUT (n) = IN (n) × G (n) (2)

  The mute gain G (n) at time n is calculated by the time constant mute unit 11 according to the equation (3).

  G (n + 1) = G (n) -MS, G (0) = 1 (3)

  However, time n = 0 represents the time constant mute start time To. The unit of time n is DSP1 or the sampling period of the audio signal. That is, the actual time when the time constant mute start time is zero is n × (sampling period).

  Therefore, as time passes, the mute gain G (n) gradually decreases according to the equation (3), and when the mute gain G (n) becomes 0 or less, the mute gain G (n) is fixed to 0. .

  As a result, the amplitude of the signal output from the time constant mute unit 11 gradually decreases, and the rate of decrease is changed according to the volume value of the volume circuit 2.

  FIG. 4 is a diagram illustrating an example of a signal output from the time constant mute unit 11 according to the first embodiment. FIG. 4A is a diagram illustrating an example of a signal output from the time constant mute unit 11 when the volume value is small. FIG. 4B is a diagram illustrating an example of a signal output from the time constant mute unit 11 when the volume value is large. Note that the audio signal output from the time constant mute unit 11 is a digital signal, but is drawn in an analog manner in FIG. 4 for explanation.

  As shown in FIG. 4, when the volume value of the volume circuit 2 is large, the mute step MS is set small. For this reason, even when the volume signal is large and the audio signal is greatly amplified in the volume circuit 2 and the amplifier circuit 3 in the subsequent stage, the mute step on the output signal is made close to or similar to that when the volume value is small. can do. If the mute step MS is set to a small value, the time until the mute is completely applied (that is, until the mute gain becomes zero) becomes longer.

  As described above, according to the first embodiment, the time constant mute unit 11 performs mute by gradually decreasing the mute gain for the input signal. Then, the mute controller 22 adjusts the rate of decrease of the mute gain by the time constant mute unit 11 according to the gain setting value of the volume. In particular, the mute control unit 22 decreases the value of the mute step in the time constant mute unit 11 in order to slow down the decrease rate of the mute gain as the gain setting value of the volume circuit 2 is larger.

  Thereby, even when the gain of the circuit portion subsequent to the time constant mute unit 11 is set higher, it is possible to suppress the occurrence of shock noise during the time constant mute.

  Further, in a situation where the level of the input signal is generally low and the volume value is set to be high, in the conventional apparatus, the level of shock noise with respect to the audio signal is relatively large and shock noise is easily noticeable. According to such a device, even in such a situation, since the mute step is adjusted according to the volume value, shock noise is suppressed regardless of the input signal level.

Embodiment 2. FIG.
The digital audio apparatus according to the second embodiment of the present invention is obtained by changing the correspondence between the volume value of the time constant mute unit 11 and the mute step in the digital audio apparatus according to the first embodiment.

  Since the configuration and operation of the digital audio apparatus according to the second embodiment are the same as those in the first embodiment except for the mute control unit 22, the description thereof is omitted.

  FIG. 5 is a diagram illustrating an example of a correspondence relationship between a volume value and a mute step value according to the second embodiment. Note that the solid line in FIG. 5 shows the correspondence between the volume value and the mute step value in the second embodiment, and the broken line shows the correspondence between the volume value and the mute step value in the first embodiment. .

  The mute control unit 22 according to the second embodiment sets the value of the mute step nonlinearly with respect to the volume value. The mute controller 22 sets the mute step to the predetermined minimum value MSmin when the volume value is equal to or greater than the predetermined threshold value Va, and sets the mute step to the predetermined maximum value when the volume value is less than the predetermined threshold value Va. Let it be the value MSmax. Since other operations of the mute control unit 22 in the second embodiment are the same as those in the first embodiment, description thereof is omitted.

  In the second embodiment, one threshold value Va for the volume value is set so that the mute step is set to one of the two values. However, N (N> 1) threshold values are provided, and the mute step is set. It may be set to any one of (N + 1) values.

  As described above, according to the second embodiment, it is possible to determine the value of the mute step only by determining the threshold condition for the volume value, and the mute control unit 22 indicates the correspondence between the volume value and the mute step value. There is no need to store the table shown or calculate the mute step value from the volume value, and the control circuit 4 can be mounted relatively easily in terms of storage capacity, arithmetic processing capability, and the like.

Embodiment 3 FIG.
The digital audio device according to the third embodiment of the present invention is obtained by changing the correspondence between the volume value of the time constant mute unit 11 and the mute step in the digital audio device according to the first embodiment.

  The configuration and operation of the digital audio apparatus according to the third embodiment are the same as those in the first embodiment except for the mute control unit 22, and thus the description thereof is omitted.

  FIG. 6 is a diagram illustrating an example of a correspondence relationship between a volume value and a mute step value according to the third embodiment. The solid line in FIG. 6 shows the correspondence between the volume value and the mute step value in the third embodiment, and the broken line shows the correspondence between the volume value and the mute step value in the first embodiment. .

  The mute controller 22 in the third embodiment sets the value of the mute step nonlinearly with respect to the volume value. The mute controller 22 decreases the adjustment amount of the mute step in the region where the volume value is small, and increases the adjustment amount of the mute step in the region where the volume value is large. That is, the greater the volume value, the greater the adjustment amount of the mute step. The mute controller 22 in the third embodiment calculates the mute step value from the volume value with such characteristics by calculating the mute step value using a second-order or higher (for example, third order) polynomial having the volume value as a variable. Can be calculated. Alternatively, as in the first embodiment, the mute step value may be determined from the volume value with such characteristics using a table.

  Note that other operations of the mute control unit 22 in the third embodiment are the same as those in the first embodiment, and thus description thereof is omitted.

  As described above, according to the third embodiment, since the mute step does not change abruptly according to the volume gain, it is not necessary to give a sense of incongruity due to the change of the time constant mute before and after the fine adjustment of the volume gain. Moreover, since the shock noise is more strongly suppressed in the region where the volume value where the shock noise is conspicuous is larger, the shock noise can be made less conspicuous in terms of hearing.

Embodiment 4 FIG.
In the digital audio device according to the fourth embodiment, the volume circuit 2 in the digital audio device according to the first embodiment is arranged before the DSP 1 (time constant mute unit 11).

  Since the other configuration and operation of the digital audio apparatus according to the fourth embodiment are the same as those in any of the first to third embodiments, description thereof is omitted. Even in this case, the same effect can be obtained.

  Each embodiment described above is a preferred example of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. It is.

  For example, in each of the above-described embodiments, the volume circuit 2 is an electronic volume that is a digital circuit, but may instead be an analog volume provided in an analog circuit portion at a subsequent stage. In that case, instead of the volume control unit 21, a volume value detection unit for detecting the gain setting value or volume gain of the analog volume is provided, and the value detected thereby is supplied to the mute control unit 22. Good.

  The present invention can be applied to a digital audio apparatus that reproduces a digital audio signal from audio data read from various sound sources such as a compact disc (trademark) and a minidisc (trademark).

1 is a block diagram showing a configuration of a digital audio apparatus according to Embodiment 1 of the present invention. 6 is a diagram illustrating an example of a correspondence relationship between a volume value and a mute step value according to Embodiment 1. FIG. 6 is a diagram illustrating a specific example of a correspondence relationship between a volume value and a mute step value in the first embodiment. FIG. 6 is a diagram illustrating an example of a signal output from a time constant mute unit in the first embodiment. FIG. FIG. 10 is a diagram illustrating an example of a correspondence relationship between a volume value and a mute step value in the second embodiment. FIG. 16 is a diagram illustrating an example of a correspondence relationship between a volume value and a mute step value in the third embodiment. It is a figure which shows an example of the signal at the time of applying a time constant mute. It is an enlarged view of the part of the broken-line circle | round | yen of FIG. It is a block diagram which shows the structure of the conventional digital audio apparatus. It is a figure explaining the time constant mute when a volume gain is large.

Explanation of symbols

1 Digital signal processor (DSP)
2 Volume circuit (volume)
4 Control circuit 11 Time constant mute section (muting means)
22 Mute controller (adjustment means)

Claims (6)

Muting means to mute by gradually decreasing the mute gain for the input signal,
Adjusting means for adjusting the rate of decrease of the mute gain by the muting means in accordance with the gain setting value of the volume;
A muting device comprising:   2. The muting device according to claim 1, wherein the adjusting means slows down the mute gain decreasing rate as the volume setting value is larger. A digital signal processor that reduces the mute gain by a mute step at regular intervals, and multiplies the audio signal by the mute gain.
A volume that is positioned before or after the digital signal processor and adjusts the amplitude of the audio signal;
A control circuit for setting a mute step of the digital signal processor according to a volume gain of the volume;
A digital audio apparatus comprising:   4. The digital audio apparatus according to claim 3, wherein the control circuit sets the mute step to a smaller value as the volume gain of the volume is larger.   The control circuit sets the volume gain of the volume, and when the volume gain of the volume is changed, specifies the value of the mute step according to the changed volume gain, and uses the value to determine the value of the digital signal processor. 4. The digital audio apparatus according to claim 3, wherein a value of the mute step is updated. Setting the mute gain decrease rate according to the volume gain setting value;
The step of applying mute by gradually decreasing the mute gain for the input signal at the set mute gain reduction rate,
A muting method comprising:

Images