JP2006352221A - Amplitude variable apparatus and amplitude variable method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amplitude variable apparatus and an amplitude variable method capable of suppressing deterioration in an analog output signal in the case that a level of a digital signal is varied. <P>SOLUTION: A first DA converter 1 converts a digital input signal into an analog signal. On the other hand, a multiplier means 3 multiplies a coefficient with the digital input signal, and a second DA converter 2 converts the digital input signal with which the coefficient is multiplied by the multiplier means 3 into an analog signal. Then an output means 5 outputs the sum of both the analog signals by the first DA converter 1 and the second DA converter 2 as an analog output signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an amplitude variable device and an amplitude variable method.

  For example, a sound reproducing device that reproduces an audio signal from a digital signal or digital data generally has a function of adjusting the amplitude of the output audio signal. One such mechanism is a digital volume.

  FIG. 7 is a block diagram illustrating an example of a digital volume. In the digital volume shown in FIG. 7, the coefficient unit 101 multiplies the digital data (digital signal) by a coefficient, the DA converter 102 performs DA (Digital-to-Analog) conversion on the digital data after multiplication, The converted analog signal is output. As a result, the amplitude of the audio signal (that is, the digital value) is reduced in the digital signal region, and as a result, the amplitude of the output analog signal is also reduced (see, for example, Patent Document 1).

  Normally, in such a digital volume, when the volume is maximum, the digital input signal is directly DA-converted and the converted analog signal is output as it is. On the other hand, when the volume is not maximum (when the volume is reduced), a digital signal multiplied by a coefficient of 0 or more and 1 or less is DA-converted, and the converted analog signal is output as it is. In other words, when the volume is maximum, the amount of attenuation at the digital volume is zero, and when the volume is not maximum, the amplitude of the analog signal is attenuated compared to the maximum value by the amount of attenuation according to the coefficient value at the time of multiplication To do.

  In addition, in such a digital volume, in order to avoid losing the resolution of the digital signal due to a decrease in the amplitude in the digital signal area, DA conversion having a higher resolution than the resolution (that is, the dynamic range) of the digital signal. A vessel may be employed. For example, since the resolution of a digital signal by a compact disk is 16 bits (96 dB, 6 dB / bit), a DA converter having a resolution of 24 bits is used. In this case, if the attenuation of the signal in the coefficient unit 101 in the digital signal region is 48 decibels (that is, 8 bits) or less, the digital signal after attenuation is converted to a DA converter while maintaining the resolution of the digital input signal. 102 can be input.

JP 2000-138585 A (FIG. 2 etc.)

  However, if the resolution of the digital signal and the resolution of the DA converter are approximately the same, the resolution of the attenuated digital signal input to the DA converter will be reduced, resulting in increased quantization noise. The S / N ratio is lower than when the digital signal is not attenuated. In particular, in a device with a wide volume adjustment range, during normal playback, playback is often performed at a volume attenuated from the maximum value, and degradation of sound quality in a normal use state becomes a problem.

  Further, as described above, when the resolution of the DA converter is made larger than the resolution of the digital signal, the above problem is solved under a certain condition, but when the attenuation is increased (in the above example, 48 dB). A similar problem occurs.

  An object of the present invention is to provide an amplitude variable device and an amplitude variable method capable of suppressing deterioration of an analog output signal when the amplitude is varied in a digital signal region.

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

  One of the amplitude variable devices according to the present invention includes a first DA converter that converts a digital input signal into an analog signal, a multiplying unit that multiplies the digital input signal by a coefficient, and a multiplier that multiplies the coefficient by the multiplier. The second DA converter that converts a digital input signal into an analog signal and the sum of both the analog signal from the first DA converter and the analog signal from the second DA converter or the difference between one and the other is output as an analog output Output means for outputting as a signal.

  In addition to the amplitude variable device described above, the amplitude variable device according to the present invention may be configured as follows. That is, in that case, the value of the coefficient of the multiplication means is variable.

  In addition to the amplitude variable device described above, the amplitude variable device according to the present invention may be configured as follows. That is, in that case, the multiplication means can set the coefficient value to either positive or negative.

  In addition to the amplitude variable device described above, the amplitude variable device according to the present invention may be configured as follows. In other words, in this case, the amplitude variable device further includes a control circuit that changes the value of the coefficient in the multiplication means when adjusting the amplitude of the analog output signal output from the output means.

  One of the amplitude variable devices according to the present invention includes a first DA converter that converts a digital input signal into an analog signal, a multiplying unit that multiplies the digital input signal by a coefficient, and a multiplier that multiplies the coefficient by the multiplier. A second DA converter that converts a digital input signal into an analog signal, and an analog signal from the second DA converter combined with an analog signal from the first DA converter in a reverse phase, and a combined signal Is output as an analog output signal.

  One of the amplitude variable devices according to the present invention is a first multiplication means for multiplying a digital input signal by a first coefficient, and a first for converting the digital input signal after being multiplied by the first coefficient to an analog signal. A DA converter, second multiplying means for multiplying the digital input signal by a second coefficient, a second DA converter for converting the digital input signal after being multiplied by the second coefficient to an analog signal, Output means for outputting the sum of the analog signal from the first DA converter and the analog signal from the second DA converter or the difference between one and the other as an analog output signal.

  One of the amplitude variable devices according to the present invention is a first multiplication means for multiplying a digital input signal by a first coefficient, and a first for converting the digital input signal after being multiplied by the first coefficient to an analog signal. A DA converter, second multiplying means for multiplying the digital input signal by a second coefficient, a second DA converter for converting the digital input signal after being multiplied by the second coefficient to an analog signal, Output means for synthesizing the analog signal from the second DA converter in reverse phase with the analog signal from the first DA converter and outputting the synthesized signal as an analog output signal.

  In addition to the amplitude variable device described above, the amplitude variable device according to the present invention may be configured as follows. That is, in this case, the amplitude variable device includes a control circuit that sets the value of the first and / or second coefficient in accordance with the attenuation amount of the analog output signal. The control circuit sets the value of the second coefficient to zero when the absolute value of the second coefficient is equal to or less than a predetermined value for a certain attenuation, and sets the first coefficient to a value corresponding to the attenuation. Set to.

  In addition to the amplitude variable device described above, the amplitude variable device according to the present invention may be configured as follows. That is, in this case, when the attenuation amount of the analog output signal is larger than 0.5, the control circuit sets the first coefficient to 1, sets the second coefficient to a value corresponding to the attenuation amount, and sets the analog output signal. When the amount of attenuation is smaller than 0.5, the second coefficient is set to zero, and the first coefficient is set to a value corresponding to the amount of attenuation.

  One of the amplitude variable methods according to the present invention converts a digital input signal into a first analog signal, multiplies the digital input signal by a coefficient, and multiplies the digital input signal after the coefficient into a second analog signal. Converting and outputting the sum of both the first and second analog signals or the difference between one and the other as an analog output signal.

  One of the amplitude variable methods according to the present invention is to multiply a digital input signal by a first coefficient, convert the digital input signal after being multiplied by the first coefficient to a first analog signal, and convert the digital input signal to a digital input signal. Multiply the second coefficient, convert the digital input signal after the second coefficient to the second analog signal, and calculate the sum of both the first and second analog signals or the difference between one and the other Output as an analog output signal.

  According to the present invention, it is possible to obtain an amplitude variable device and an amplitude variable method capable of suppressing degradation of an analog output signal when amplitude is varied in a digital signal region.

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

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of an amplitude variable device according to Embodiment 1 of the present invention. In FIG. 1, a DA converter (DAC) 1 is a first DA converter that converts a digital input signal into an analog signal. The DA converter (DAC) 2 is a second DA converter that converts the digital input signal after being multiplied by the coefficient by the coefficient unit 3 into an analog signal. The resolution of the DA converters 1 and 2 may be the same as the resolution of the digital input signal, or may be higher than the resolution of the digital input signal.

  The coefficient unit 3 is a circuit that multiplies the digital signal by a coefficient having a certain value. The coefficient unit 3 includes, for example, a multiplier and a storage unit such as a memory that stores coefficient data. The control circuit 4 is a circuit that sets the value of the coefficient in the coefficient unit 3.

  The adder 5 is a circuit that functions as an output unit that calculates the sum of both the analog signal from the DA converter 1 and the analog signal from the DA converter 2 and outputs the result as an analog output signal.

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

  First, the same digital input signal from a digital audio playback device or the like is supplied to the DA converter 1 and the coefficient unit 3.

  The DA converter 1 converts the digital input signal into an analog signal and supplies it to the adder 5.

  On the other hand, the coefficient unit 3 multiplies the digital input signal by a coefficient having a value set by the control circuit 4 and supplies the digital input signal after the multiplication to the DA converter 2. The DA converter 2 converts the digital input signal after the multiplication into an analog signal and supplies it to the adder 5.

  The adder 5 calculates the sum of the analog signal from the DA converter 1 and the analog signal from the DA converter 2 and outputs it as an analog output signal.

  In addition, the control circuit 4 causes the coefficient unit 3 to store digital data of coefficient values. When the analog output signal is attenuated, the control circuit 4 sets the coefficient to a negative value larger than −1 and smaller than 0, for example, according to the operation amount of an operation on a volume operation unit (not shown). The analog signals input from the DA converters 1 and 2 to the adder 5 are in opposite phases, and the amplitude of the analog signal from the DA converter 2 is smaller than the amplitude of the analog signal from the DA converter 1. The analog output signal from the adder 5 is attenuated. At this time, the closer the coefficient value is to -1, the greater the attenuation of the analog output signal. When the coefficient of the coefficient unit 3 is α, the attenuation amount of the analog output signal is expressed by the equations (1) and (2). Therefore, the control circuit 4 sets the coefficient value corresponding to the attenuation amount as the coefficient of the coefficient unit 3 based on the equations (1) and (2).

  α = (Attenuation amount of analog output signal) −1 (1)

Attenuation [decibel] = 20 × log ₁₀ (1 + α) (2)

  FIG. 2 is a diagram illustrating a correspondence relationship between the attenuation amount of the analog output signal and the coefficient value of the coefficient unit 3 according to the first embodiment. When the coefficient value of the coefficient unit 3 is positive, the attenuation amount becomes negative and the analog output signal is amplified.

  FIG. 3 is a diagram showing an analog output signal when the attenuation is 6 dB in the first embodiment. FIG. 4 is a diagram illustrating an analog output signal when the attenuation is 24 decibels in the first embodiment. FIG. 5 is a diagram showing an analog output signal when the attenuation is 1 dB in the first embodiment. 3, 4, and 5, the analog signal from the DA converter 1 is a normal phase output signal, the analog signal from the DA converter 2 is a negative phase output signal, and the analog output from the adder 5 is The signal is an output signal, and the amplitude of the positive phase output signal is 1.

  In the case of FIG. 3, the coefficient value of the coefficient unit 3 is set to -0.49881, in the case of FIG. 4, the coefficient value of the coefficient unit 3 is set to -0.09369, and in the case of FIG. The coefficient value of the coefficient unit 3 is set to −0.10875.

  Note that the control circuit 4 may cause the analog output signal to fade in or fade out by changing the coefficient value of the coefficient unit 3 continuously or stepwise over time.

  In addition, the upper limit of the dynamic range of the signal processing system in the digital signal region is generally matched with the upper limit of the dynamic range of the digital signal, and no headroom margin is generally provided. For this reason, digital signals in the digital signal region are usually not amplified. Therefore, when various kinds of signal processing are performed on a digital signal by a digital signal processor (DSP) or the like under such conditions, in order to prevent overflow at the time of signal processing by the DSP or the like, the digital signal is processed by a predetermined headroom margin. Signal processing is performed after attenuation. However, since the conventional digital volume does not have an amplification function, the attenuation amount due to this attenuation is not compensated, and when the signal processing by this DSP or the like is turned on / off, the amplitude of the output signal becomes discontinuous. That is, a volume difference occurs when signal processing by a DSP or the like is turned on / off. In such a situation, in the amplitude variable device according to the first embodiment, the control circuit 4 sets the coefficient to a positive value when the signal processing is in an on state according to such an on / off state of the signal processing (that is, The volume difference may be compensated by setting the attenuation amount to be negative. For example, if the coefficient value is set to 0.995262, the analog output signal is amplified by 6 dB.

  As described above, according to the first embodiment, the DA converter 1 as the first DA converter converts a digital input signal into an analog signal. On the other hand, the coefficient unit 3 as a multiplication means multiplies the digital input signal by a coefficient, and the DA converter 2 as the second DA converter converts the digital input signal after being multiplied by the coefficient by the coefficient unit 3 into an analog signal. Convert to The adder 5 as output means outputs the sum of both the analog signal from the DA converter 1 and the analog signal from the DA converter 2 as an analog output signal. That is, when the analog output signal is attenuated, the adder 5 combines the analog signal from the DA converter 2 with the analog signal from the DA converter 1 in reverse phase, and the combined signal is converted into the analog output signal. Output as.

  As a result, when the attenuation amount of the analog output signal is large as shown in FIG. 4, the amplitude of the signal input to the two DA converters 1 and 2 is maintained at the same level as the amplitude of the digital input signal. Therefore, the resolution of the input signals to the DA converters 1 and 2 is maintained during DA conversion. On the other hand, when the attenuation is small as shown in FIG. 5, the resolution of the input signal to the DA converter 2 is lowered, but the amplitude of the output signal from the DA converter 2 is small. The influence on the analog output signal is small. Therefore, according to the first embodiment, deterioration of the analog output signal can be suppressed when the amplitude is varied in the digital signal region.

  Further, according to the first embodiment, the coefficient unit 3 can set the coefficient value to either positive or negative. As a result, the analog output signal can be amplified in addition to the attenuation of the analog output signal only by changing the sign of the coefficient with the same circuit configuration.

Embodiment 2. FIG.
The amplitude variable device according to the second embodiment of the present invention is such that the positive phase signal is multiplied by a coefficient in the amplitude variable device according to the first embodiment.

  FIG. 6 is a block diagram showing a configuration of an amplitude variable device according to Embodiment 2 of the present invention. In FIG. 6, a coefficient unit 11 is a circuit that multiplies a digital signal by a coefficient having a certain value. The coefficient unit 11 includes, for example, a multiplier and a storage unit such as a memory that stores coefficient data. The control circuit 12 is a circuit for setting coefficient values in the coefficient multiplier 3 and the coefficient multiplier 11.

  The other components in FIG. 6 are the same as those in the first embodiment, and a description thereof is omitted.

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

  First, the same digital input signal from a digital audio reproduction device or the like is supplied to the coefficient multiplier 11 and the coefficient multiplier 3.

  The coefficient unit 11 multiplies the digital input signal by the coefficient of the value set by the control circuit 12 and supplies the digital input signal after the multiplication to the DA converter 1. The DA converter 1 converts the digital input signal after the multiplication into an analog signal and supplies it to the adder 5.

  On the other hand, the coefficient unit 3 multiplies the digital input signal by a coefficient having a value set by the control circuit 12 and supplies the digital input signal after the multiplication to the DA converter 2. The DA converter 2 converts the digital input signal after the multiplication into an analog signal and supplies it to the adder 5.

  The adder 5 calculates the sum of the analog signal from the DA converter 1 and the analog signal from the DA converter 2 and outputs it as an analog output signal.

  The control circuit 12 sets coefficient values in the coefficient multiplier 3 and the coefficient multiplier 11. When the control circuit 12 attenuates the analog output signal, for example, the coefficient of the coefficient unit 11 is set to 1 and the coefficient of the coefficient unit 3 is set to be larger than −1 and 0 in accordance with the operation amount of the volume operation unit (not shown). A smaller negative value is set, or the coefficient of the coefficient unit 3 is set to 0, and the coefficient of the coefficient unit 11 is set to a negative value larger than 0 and smaller than 1. At this time, the closer the coefficient value of the coefficient unit 3 is to −1 and the closer the coefficient value of the coefficient unit 11 is to 0, the greater the attenuation amount of the analog output signal. When the coefficient of the coefficient unit 3 is α and the coefficient of the coefficient unit 11 is β, the attenuation amount of the analog output signal is expressed by the equations (3) and (4). Therefore, the control circuit 12 sets the coefficient value corresponding to the attenuation amount as the coefficient of the coefficient multipliers 3 and 11 based on the equations (3) and (4).

  α = (Attenuation amount of analog output signal) −β (3)

Attenuation [decibel] = 20 × log ₁₀ (α + β) (4)

  In the second embodiment, when the attenuation amount of the analog output signal is larger than 0.5, the control circuit 12 sets the coefficient β to 1, sets the coefficient α to a value corresponding to the attenuation amount, and outputs the analog output. When the signal attenuation is smaller than 0.5, the coefficient α is set to zero, and the coefficient β is set to a value corresponding to the attenuation. For example, when the attenuation amount of the analog output signal is 1 dB, the coefficient β is set to 0.891251 and the coefficient α is set to 0.

  As described above, according to the second embodiment, the coefficient unit 11 serving as the first multiplying unit multiplies the digital input signal by the first coefficient β, and the DA converter 1 serving as the first DA converter. Converts the digital input signal after being multiplied by the first coefficient β to an analog signal. On the other hand, the coefficient multiplier 3 as the second multiplication means multiplies the digital input signal by the second coefficient α, and the DA converter 2 as the second DA converter multiplies the digital coefficient after the second coefficient α is multiplied. Convert input signal to analog signal. The adder 5 as output means outputs the sum of both the analog signal from the DA converter 1 and the analog signal from the DA converter 2 as an analog output signal. That is, when the analog output signal is attenuated, the adder 5 combines the analog signal from the DA converter 2 with the analog signal from the DA converter 1 in reverse phase, and the combined signal is converted into the analog output signal. As output.

  Thereby, it is possible to suppress the deterioration of the analog output signal when the amplitude is varied in the digital signal region.

  Further, according to the second embodiment, the control circuit 12 sets the value of the first coefficient β and / or the second coefficient α according to the attenuation amount of the analog output signal. When the absolute value of the second coefficient α is equal to or less than a predetermined value for a certain attenuation, the control circuit 12 sets the value of the second coefficient α to zero and sets the first coefficient β to the attenuation. Set the value according to. In particular, when the attenuation amount of the analog output signal is larger than 0.5, the control circuit 12 sets the first coefficient β to 1 and sets the second coefficient α to a value corresponding to the attenuation amount. Is less than 0.5, the second coefficient α is set to zero, and the first coefficient β is set to a value corresponding to the attenuation. When the attenuation is in units of 1 decibel, when the attenuation is 7 decibels or more, the first coefficient β is set to 1, the second coefficient α is set to a value corresponding to the attenuation, and the attenuation is Is 6 dB or less, the second coefficient α is set to zero, and the first coefficient β is set to a value corresponding to the amount of attenuation.

  As a result, the resolution of the input signals to the DA converters 1 and 2 can be maintained satisfactorily regardless of the amount of attenuation of the analog output signal, and the deterioration of the analog output signal when the amplitude is varied in the digital signal region is suppressed. be able to.

  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 first and second embodiments, the coefficient of the coefficient unit 3 is set to a value larger than 0 and smaller than 1, and instead of the adder 5, the output signal of the DA converter 1 is output from the output signal of the DA converter 1. A subtractor that subtracts the signal may be used. Even in this case, the output signal from the DA converter 2 is synthesized in reverse phase with respect to the output signal from the DA converter 1.

  In each of the first and second embodiments, the coefficient values of the coefficient multipliers 3 and 11 may be fixed. In that case, the control circuits 4 and 12 are not particularly necessary.

  The present invention is applicable to a volume of a digital audio device, for example.

It is a block diagram which shows the structure of the amplitude variable apparatus which concerns on Embodiment 1 of this invention. 6 is a diagram illustrating a correspondence relationship between an attenuation amount of an analog output signal and a coefficient value of a coefficient device in Embodiment 1. FIG. 6 is a diagram showing an analog output signal when the attenuation is 6 dB in the first embodiment. FIG. 6 is a diagram illustrating an analog output signal when the attenuation is 24 decibels in Embodiment 1. FIG. 6 is a diagram illustrating an analog output signal when the attenuation is 1 dB in the first embodiment. FIG. It is a block diagram which shows the structure of the amplitude variable apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows an example of a digital volume.

Explanation of symbols

1 DA converter (first DA converter)
2 DA converter (second DA converter)
3 Coefficient multiplier (multiplication means, second multiplication means)
4,12 Control circuit 5 Adder (output means)
11 Coefficient multiplier (first multiplication means)

Claims (11)

A first DA converter for converting a digital input signal into an analog signal;
Multiplying means for multiplying the digital input signal by a coefficient;
A second DA converter for converting the digital input signal after being multiplied by the coefficient by the multiplication means into an analog signal;
Output means for outputting a sum of both of the analog signal from the first DA converter and the analog signal from the second DA converter or a difference between one and the other as an analog output signal;
An amplitude variable device comprising:   2. The amplitude variable device according to claim 1, wherein the value of the coefficient of the multiplication means is variable.   3. The amplitude variable apparatus according to claim 1, wherein the multiplication means can set the value of the coefficient to either positive or negative.   4. The control circuit according to claim 1, further comprising: a control circuit that changes a value of the coefficient in the multiplication unit when adjusting an amplitude of an analog output signal output from the output unit. 5. The amplitude variable device according to claim 1. A first DA converter for converting a digital input signal into an analog signal;
Multiplying means for multiplying the digital input signal by a coefficient;
A second DA converter for converting the digital input signal after being multiplied by the coefficient by the multiplication means into an analog signal;
Output means for synthesizing the analog signal from the second DA converter in reverse phase with the analog signal from the first DA converter, and outputting the synthesized signal as an analog output signal;
An amplitude variable device comprising: First multiplying means for multiplying the digital input signal by a first coefficient;
A first DA converter that converts the digital input signal after being multiplied by the first coefficient into an analog signal;
Second multiplying means for multiplying the digital input signal by a second coefficient;
A second DA converter that converts the digital input signal multiplied by the second coefficient to an analog signal;
Output means for outputting a sum of both of the analog signal from the first DA converter and the analog signal from the second DA converter or a difference between one and the other as an analog output signal;
An amplitude variable device comprising: First multiplying means for multiplying the digital input signal by a first coefficient;
A first DA converter that converts the digital input signal after being multiplied by the first coefficient into an analog signal;
Second multiplying means for multiplying the digital input signal by a second coefficient;
A second DA converter that converts the digital input signal multiplied by the second coefficient to an analog signal;
Output means for synthesizing the analog signal from the second DA converter in reverse phase with the analog signal from the first DA converter, and outputting the synthesized signal as an analog output signal;
An amplitude variable device comprising: A control circuit for setting a value of the first and / or second coefficient according to an attenuation amount of the analog output signal;
The control circuit sets the value of the second coefficient to zero when the absolute value of the second coefficient is less than or equal to a predetermined value for a certain attenuation, and sets the first coefficient according to the attenuation. Set the value to
The amplitude variable device according to claim 7.   When the attenuation amount of the analog output signal is larger than 0.5, the control circuit sets the first coefficient to 1, sets the second coefficient to a value corresponding to the attenuation amount, and attenuates the analog output signal. 8. The amplitude variable apparatus according to claim 7, wherein when the amount is smaller than 0.5, the second coefficient is set to zero, and the first coefficient is set to a value corresponding to the attenuation amount. Converting the digital input signal to a first analog signal;
Multiplying the digital input signal by a coefficient, converting the digital input signal after multiplying the coefficient to a second analog signal,
Outputting the sum of both the first and second analog signals or the difference between one and the other as an analog output signal;
A variable amplitude method characterized by the above. Multiplying the digital input signal by a first coefficient, converting the digital input signal after multiplying by the first coefficient to a first analog signal,
Multiplying the digital input signal by a second coefficient, converting the digital input signal after multiplying the second coefficient to a second analog signal,
Outputting the sum of both of the first and second analog signals or the difference between one and the other as an analog output signal;
A variable amplitude method characterized by the above.

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