JP4007151B2 - Volume control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a volume control circuit suitable for use in an audio apparatus such as a home theater system using a digital surround system.
[0002]
[Prior art]
FIG. 8 shows a schematic configuration of a home theater system using a conventional volume control circuit. A 5.1ch digital surround signal from a DVD player or the like is compressed and encoded by a method such as Dolby Digital or DTS, and the digital bit stream is sent to a surround decoder 1 by a DSP-LSI (digital signal processor-large scale integrated circuit). Entered. The bit stream is decoded in the surround decoder 1 based on each method and restored to a 5.1ch digital multi-channel signal as shown in the figure. The 5.1ch digital multi-channel signal is output through the first variable gain units 2, 2... For volume adjustment, converted to an analog signal by the DAC (D / A converter) 3, and the multi-channel power. Through the amplifier 4, the signals are output to the front woofers L, C, R, left and right surround LS, RS signals, and the subwoofer SW responsible for bass.
[0003]
A volume knob 7 is shown as an example of operation means provided for volume adjustment. The internal gain setting and amplitude state in a general design example will be described. At the 0 dB position of the volume knob 7, the variable gain section 2 for the digital signal in FIG. 8 is set to 0 dB, and the output of the surround decoder 1 is directly sent to the DAC 3. Entered. After being converted to an analog signal by the DAC 3, it is input to the power amplifier 4. The gain of the power amplifier 4 is determined so that the maximum possible amplitude of the output of the power amplifier 4 can be obtained at the maximum output amplitude of the DAC 3. That is, in this state, the decoded waveform at the maximum output is output to the speaker without loss.
[0004]
When the volume knob 7 is turned to the + side, a signal at a level lower than the rated level can be heard at a higher volume. On the other hand, when the dial is turned to the-side, the decoded signal is attenuated to a small extent, so that the volume can be lowered and heard. FIG. 9 shows a correspondence relationship between the gain of the variable gain unit 2 and the gain set by the volume knob 7. The gain of the variable gain unit 2 is set according to the volume designation gain designated at the position of the knob 7.
[0005]
Now, the volume adjustment by this method does not require a dedicated part for volume adjustment, and thus has a feature that the function can be realized without increasing the cost. However, when listening at a low volume, there is a disadvantage that the residual noise of the DAC 3 is relatively increased and the sound quality is impaired. FIG. 10 shows the state of S / N (signal to noise ratio) degradation during listening to a small volume when a 16-bit DAC is used for DAC3. If the DAC 3 main body has an ideal 16-bit DAC performance, and a 16-bit full-bit signal is 0 dB, the residual noise is approximately −96 dB, and the S / N value, which is the ratio of the signal and noise, is 96 dB. In the -30 dB state where the volume is lowered, the output of the DAC 3 is -30 dB, while the residual noise remains unchanged -96 dB, so the S / N value has deteriorated to 66 dB. Similarly, the distortion was also degraded by −30 dB = 5 bits from the 16-bit resolution.
[0006]
FIG. 11 is a block diagram showing a schematic configuration of a home theater system to which another conventional volume adjustment circuit is applied. In this system, variable gain sections 5, 5,... For analog signals are provided after the DAC 3 for volume adjustment. FIG. 12 shows the relationship between the designated gain of the volume knob 7 and the gain of the variable gain unit 5. The input signal of the DAC 3 does not depend on the volume adjustment value, and the resolution is maintained as it is. The problem is that in the state where the listening volume is greatly increased with the volume position of 0 dB or more, the residual noise of the DAC 3 is enlarged and heard, so that the residual noise increased when no signal is input is heard as shown in FIG. was there. In the state of listening at a reduced listening volume, it can be said that, for example, when −50 dB is designated as shown in the numerical example of the figure, the noise amount is attenuated beyond the practically required range of −146 dB. In addition, since the entire gain adjustment range is realized by the variable gain unit 5 in this circuit, in the case of an electronic volume composed of a plurality of resistors and electronic switches, a large number of electronic switch circuits and resistors are required, and the cost is reduced. It was up.
[0007]
Patent Documents 1 to 4 are known as other conventional circuit examples. These will be described below.
(1) Patent Document 1
As shown in Fig. 1, the digital signal processing unit is equipped with a digital volume and an analog volume after D / A conversion. When the gain exceeds 1, the analog volume is fixed at gain 1, and the digital volume is set to the required gain. Below 1, the digital volume gain is fixed to 1 and the necessary gain setting is performed with the analog volume.
[0008]
In this prior art, the gain is set with the analog volume up to the minimum gain, so that the performance required for the analog volume is severe. For example, in the case of a mechanical volume that obtains the desired attenuation by mechanically changing the contact position using a resistor applied on the substrate as a dividing resistor, the attenuation is accurate in a narrowing area exceeding -60 dB (1/1000). Therefore, it is difficult to obtain a good volume level of each channel, which is important in multi-channel surround playback, at a low volume. As described in this prior art, when a variable gain amplifier called VCA is used, there is a disadvantage that a certain amount of amplifier residual noise of about −100 dB remains. Further, when the circuit is configured with a circuit that obtains a desired division ratio by providing a large number of resistors and switching with an electronic switch, a large number of electronic switches are required according to the amount of narrowing down, resulting in high costs.
[0009]
(2) Patent Document 2
This prior art is a technique in which the switching gain position is made arbitrary and the degree of freedom is increased in accordance with the state of digital signal processing with respect to that described in Patent Document 1, and the maximum narrowing amount below a certain gain value is reduced to D. This is the same as that of Patent Document 1 in that it is performed with the volume after the / A conversion, and the problem that Patent Document 1 has similarly exists.
[0010]
(3) Patent Document 3
The block diagram shown in FIG. 1 of Patent Document 3 is the same as the basic configuration of the invention shown in FIG. The novel point of this Patent Document 3 is that one of the two points of the digital domain and the analog domain is the main adjustment, the other is the fine adjustment, and the fineness of the desired adjustment step can be realized economically in combination. Secondary, reduction of residual noise is obtained according to the attenuation after D / A conversion. In this way, when the adjustment of a wide step but a coarse step is combined with the adjustment of a small step but a fine step, it is difficult to make the difference in attenuation realized by each switching combination uniform. It is difficult to obtain a monotonous increase / decrease property when continuously changing.
[0011]
Further, this Patent Document 3 does not have a concept of using a digital attenuator and an analog attenuator separately according to the volume variable region. In addition, this Patent Document 3 discusses that an analog electronic volume having good characteristics is expensive and that it is difficult to manufacture, and mentions a problem that is aimed to be solved in the present application.
[0012]
(4) Patent Document 4
This patent document 4 is an invention for adjusting the volume by interlockingly controlling the digital gain control in the digital signal processing unit and the D / A conversion gain of the D / A converter itself, and varying the D / A conversion gain. In order to reduce the accompanying characteristic deterioration, the gain control of the digital part is also used. It differs from the present application in that the gain adjustment of the analog unit uses the conversion gain of the D / A converter. In general, the method of changing the conversion gain by changing the reference voltage of the D / A converter has a drawback that it is characteristically deteriorated with an increase in distortion and noise.
[0013]
[Patent Document 1]
Japanese Patent Publication No. 4-45004 [Patent Document 2]
JP 2000-174574 A [Patent Document 3]
JP-A-9-153748 [Patent Document 4]
JP 58-146114 A [0014]
[Problems to be solved by the invention]
The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to minimize the residual noise of the DAC and to minimize the cost increase due to the use of multistage volumes for analog signals. An object of the present invention is to provide a sound volume adjustment circuit that can perform the above-described operation.
[0017]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the invention according to claim 1 converts digital musical tone data into an analog signal by a digital / analog converter, and amplifies and outputs the analog signal. In a volume control circuit in an audio device, a first variable gain unit that controls the volume of the digital musical sound data, a second variable gain unit that controls the volume of the output of the digital / analog converter, and a volume setting operator Control means for controlling each gain of the first variable gain section and the second variable gain section based on a set value in the control section, wherein the control means is configured such that the volume setting operator is equal to or greater than a first value. Is specified, the gain of the second variable gain unit is set to a constant value, while the gain of the first variable gain unit is set to a value corresponding to the set value of the volume setting operator. When the setting operator specifies a volume that is less than or equal to the first value and greater than the second value, the gain of the first variable gain unit is set to a constant value while the gain of the second variable gain unit is set to a constant value. When the volume setting operator designates a volume equal to or lower than the second value, the gain of the second variable gain unit is set to a constant value. The volume control device is characterized in that the gain of the first variable gain section is set to a value corresponding to a set value of the volume setting operator.
[0018]
The invention according to claim 2, wherein the volume control device according to claim 1, relationship between the gain setting value and the first variable gain unit and the second variable gain portion of the volume setting operator When the volume setting operator designates a volume greater than or equal to a first value, the gain of the second variable gain section is set to a constant value while the first variable gain is set. When the volume setting operator specifies a volume that is equal to or less than the first value and greater than the second value, the first variable gain is set to a value corresponding to a setting value of the volume setting operator. The gain of the second variable gain unit is set to a value corresponding to the setting value of the volume setting operation element, and the volume setting operation element specifies a volume less than or equal to the second value. In this case, the gain of the second variable gain section is set to a constant value, while the first variable gain section A memory storing a gain for setting the gain of the variable gain unit to a value corresponding to a set value of the volume setting operator; and the control means stores data in the memory in accordance with an operation of the volume setting operator. The gain of the first variable gain unit and the second variable gain unit is controlled based on the read and read data.
[0019]
The invention according to claim 3, in volume control apparatus according to claim 2, wherein the control unit, the set value of the volume setting operator is corrected by the correction value previously internally stored the corrected Based on the set value, data is read from the memory, and each gain of the first variable gain unit and the second variable gain unit is controlled.
According to a fourth aspect of the present invention, in the volume control device according to any one of the first to third aspects, the first value is 0 dB.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a home theater system to which a volume control circuit according to the embodiment is applied. In this figure, portions corresponding to the respective portions in FIG. 8 and FIG. It is. In this figure, 1 is a surround decoder, 2, 2... Are a first variable gain unit for adjusting the volume of a digital channel signal output from the surround decoder 1, and 3 is an output of the first variable gain unit 2. DACs to be converted into analog signals, 5, 5,... Are second variable gain units for adjusting the volume of the analog channel signal output from the DAC 3, 4 is a power amplifier, and 7 is a volume knob. As described above, the system of FIG. 1 is different from the system of FIG. 8 in that the second variable gain unit 5 is provided in the subsequent stage of the DAC 3.
[0021]
Next, volume control in the above-described system, that is, gain control of the first variable gain unit 2 and the second variable gain unit 5 will be described.
In the figure, 11 is a microcomputer for controlling the gains of the first variable gain unit 2 and the second variable gain unit 5, and 12 to 15 are each for correcting the volume of the C channel, LS channel, RS channel, and SW channel. This is a memory in which a correction value β is stored. Reference numeral 16 denotes a memory in which a correspondence relationship between a designated gain output from the microcomputer 11 and gains to be set in the first variable gain unit 2 and the second variable gain unit 5 is stored. FIG. 2 is a diagram showing data set in the memory 16, in which A gain indicates the gain to be set in the first variable gain section 2, and B gain is set in the second variable gain section 5. Indicates the gain to be done.
[0022]
In such a configuration, when the user operates the volume knob 7, the gain α specified by the volume knob 7 after the operation is input to the microcomputer 11. The microcomputer 11 receives the gain α, and first accesses the memory 16 using the gain α as a designated gain, and reads out the A gain and the B gain corresponding to the designated gain α. For example, if the specified gain is +5 dB, as shown in FIG.
A gain = + 5db B gain = + 0dB
Is read by the microcomputer 11. The microcomputer 11 sets the A gain and B gain read from the memory 16 in the first variable gain unit 2 and the second variable gain unit 5 corresponding to each channel.
[0023]
Next, the microcomputer 11 corrects the volume of the C, LS, RS, and SW channels as necessary. This correction is intended to compensate for the difference in volume output from each speaker of the L, R, C, LS, RS, and SW channels due to the difference in speaker size, efficiency, and the like. First, for the C channel, the correction value β is read from the memory 12, and the gain α is added to the read value. The addition result is output to the memory 16 as a designated gain. FIG. 3 shows the designated gain corresponding to the gain α when the correction value β is “+5 dB”. When the specified gain described above is output to the memory 16, the A gain and the B gain corresponding to the specified gain are read from the memory 16 and output to the microcomputer 11. The microcomputer 11 sets the A gain and B gain read from the memory 16 in the first variable gain unit 2 and the second variable gain unit 5 corresponding to the C channel, respectively.
Hereinafter, similarly, the gains of the first variable gain unit 2 and the second variable gain unit 5 of the LS, RS, and SW channels are set.
[0024]
Here, the A gain and the B gain in the memory 16 are set as follows (see FIG. 2).
(1) When designated gain is 0 dB or more A gain = designated gain B gain = 0 dB
(2) When the specified gain is -36 dB to 0 dB, A gain = 0 dB
B gain = specified gain
(3) When designated gain is -36 dB or less A gain = designated gain + 36 dB
B gain = -36 dB
That is, the set value of A gain changes as shown in FIG. 4 with respect to the designated gain, and the set value of B gain changes as shown in FIG. 5 with respect to the designated gain. The total gain A × B of the A gain and the B gain is a straight line having a constant slope as shown in FIG.
[0025]
FIG. 7 is a diagram showing the magnitude of residual noise in the volume adjustment circuit in correspondence with the signal amplification gain. As shown in this figure, when the designated gain is 0 dB or more, the gain of the second variable gain unit 5 is constant, so that the residual noise is also −96 dB constant. Further, when the designated gain is 0 dB to -36 dB, the gain of the second variable gain unit 5 is sequentially reduced, and accordingly, the residual noise is also reduced. Further, when the designated gain is −36 dB or less, the gain of the second variable gain unit 5 is constant, so that the residual noise is also −132 dB constant.
[0026]
Here, the value of −36 dB which is the gain mode switching point is determined by the expected residual noise reduction effect. That is, in the case of -36 dB, the residual noise is -132 dB in the low sound volume region as described above. However, if the value is set higher than -36 dB, the residual noise also increases correspondingly, and the S / N deteriorates. Therefore, this switching point is determined from the residual noise value and the S / N value.
[0027]
As described above, in the above embodiment, in the range where the specified gain is 0 dB or more, the residual noise does not change and is constant at −96 dB, and noise that deteriorates to −76 dB as shown in FIG. There is no increase. Further, when the designated gain is in the range of 0 dB to -36 dB, the residual noise also attenuates in proportion to the signal, and no increase in noise accompanied by S / N deterioration as shown in FIG. In addition, in the range where the specified gain is −36 dB or less, the residual noise is constant at −132 dB, but is a sufficiently low value.
[0028]
As described above, in the above-described embodiment, good overall characteristics can be obtained by providing the second variable gain section 5 for 36 dB and performing special control. In this case, if the second variable gain section 5 is set to 1 dB step, the control switch may be 36 steps. In the conventional one shown in FIG. 11, the cost is about 1/3 compared with the case where a control switch of 100 steps is required. In addition, a method of providing a correction value β for correcting the volume difference between the speakers is also necessary while maintaining the improvement effect of this system in the same manner by correcting the gain α which is the setting value of the volume knob 7. The correction effect is obtained.
[0029]
The gain mode switching point −36 dB described above is determined with the aim of improving the minimum residual noise to approximately the audible limit value in accordance with the actual residual noise performance of the DAC 3 to be used. That is, when the residual noise capability value of the DAC to be used is -96 dB when the 16-bit phase or the like is selected, -36 dB is selected, and -132 dB is obtained as the minimum residual noise when listening to a small volume, and the minimum audible level generally called -120 to -130 dB It has been reduced to the following. Similarly, for example, when the residual noise capability value of the used DAC is −108 dB such as an 18-bit phase, if −24 dB is selected as the switching point, the minimum residual noise at the time of listening to a small volume can be set to −132 dB.
[0030]
Further, in the method of changing the conversion gain by changing the DAC reference voltage or the like as described in the prior art, characteristics are deteriorated with an increase in distortion and noise. In the present embodiment, the D / A conversion gain is fixed, D / A conversion is performed under the most advantageous conditions, and then an economical and excellent volume control function is provided.
[0031]
【The invention's effect】
As described above, according to the present invention, it is possible to minimize the residual noise of the DAC, and therefore, it is possible to obtain a good S / N, and to increase the cost by using a multistage volume for an analog signal. There is also an effect that can be minimized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a home theater system to which a volume adjustment circuit according to an embodiment of the present invention is applied.
FIG. 2 is a diagram showing data in a memory 16 in the same embodiment.
FIG. 3 is a diagram showing a relationship example between a set value α, a correction value β and a designated gain of the volume knob 7 in the same embodiment;
FIG. 4 is a diagram showing a gain change of the first variable gain section 2 in the same embodiment.
FIG. 5 is a diagram showing a gain change of a second variable gain section 5 in the same embodiment.
FIG. 6 is a diagram showing a change in total gain of the first variable gain unit 2 and the second variable gain unit 5 in the same embodiment;
FIG. 7 is a diagram showing a residual noise level in correspondence with a signal level in the embodiment.
FIG. 8 is a block diagram showing a configuration of a home theater system to which a conventional volume adjustment circuit is applied.
9 is a diagram showing the relationship between the set gain of the volume knob 7 and the gain of the first variable gain section 2 in FIG. 8;
FIG. 10 is a diagram showing the residual noise level in the circuit of FIG. 8 in correspondence with the signal level.
FIG. 11 is a block diagram showing a configuration of a home theater system to which another conventional volume adjustment circuit is applied.
12 is a diagram showing the relationship between the set gain of the volume knob 7 and the gain of the second variable gain section 2 in FIG.
13 is a diagram showing the residual noise level in the circuit of FIG. 11 in correspondence with the signal level.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Surround decoder, 2 ... 1st variable gain part, 3 ... DAC, 4 ... Power amplifier, 5 ... 2nd variable gain part, 7 ... Volume knob, 11 ... Microcomputer, 12-16 ... Memory.

Claims (4)

In a volume control circuit in an acoustic device that converts digital musical sound data into an analog signal by a digital / analog converter, and amplifies and outputs the analog signal.
A first variable gain unit for controlling the volume of the digital musical sound data;
A second variable gain unit for controlling the volume of the output of the digital / analog converter;
Control means for controlling each gain of the first variable gain section and the second variable gain section based on a set value in a volume setting operator;
Comprising
The control means sets the gain of the second variable gain unit to a constant value while the gain of the first variable gain unit is set to a constant value when the volume setting operator designates a volume equal to or higher than the first value. A value corresponding to the setting value of the volume setting operator,
When the volume setting operator designates a volume that is less than or equal to the first value and greater than the second value, the gain of the first variable gain section is set to a constant value, while the second variable gain section The gain is set to a value corresponding to the set value of the volume setting operator,
When the volume setting operator designates a volume less than or equal to the second value, the gain of the second variable gain section is set to a constant value, while the gain of the first variable gain section is set to the volume setting operation. A volume control device characterized by having a value corresponding to a set value of a child. A memory that stores a correspondence relationship between a set value of the volume setting operator and the gains of the first variable gain unit and the second variable gain unit, wherein the volume setting operator is equal to or greater than a first value. Is specified, the gain of the second variable gain unit is set to a constant value, while the gain of the first variable gain unit is set to a value corresponding to the set value of the volume setting operator. When the setting operator specifies a volume that is less than or equal to the first value and greater than the second value, the gain of the first variable gain unit is set to a constant value while the gain of the second variable gain unit is set to a constant value. When the volume setting operator designates a volume equal to or lower than the second value, the gain of the second variable gain unit is set to a constant value. The gain of the first variable gain section is set to a value corresponding to the set value of the volume setting operator. Comprising a memory storing the gain,
The control means reads data in the memory in response to an operation of the volume setting operator, and controls gains of the first variable gain unit and the second variable gain unit based on the read data. The volume control device according to claim 1 . The control means corrects a setting value of the volume setting operator using a correction value stored in advance, reads data from the memory based on the corrected setting value, and the first variable gain unit The volume control device according to claim 2 , wherein each gain of the second variable gain unit is controlled. Volume control apparatus according to any one of claims 1 to claim 3, wherein the first value is 0 dB.

Images