JPS63300612A - Sound volume adjusting device in digital audio system - Google Patents

Abstract

PURPOSE:To obtain a sound volume adjusting device with a wide adjusting range and less distortion by providing 1st and 2nd analog sound volume adjusting means and a control section selecting the combination of sound volume adjusting means in response to the indicated sound volume adjusting level. CONSTITUTION:With switches 11, 12 of the 1st analog sound volume adjusting means 13 opened, a feedback element of a current/voltage converter (IVC) 3 is only a resistor R10 to bring the attenuation to 0dB. With the switch 11 closed, the attenuation is 6dB and when both the switches are closed, the attenua tion is 12dB. On the other hand, the 2nd analog sound volume adjusting means 14 offers an attenuation of 0dB with the switches 21, 22 opened and gives an attenuation of 12dB with the switch 21 closed. When both the switches are closed, the attenuation is set to be 24dB. The switches 11, 12 and 21, 22 are switched by a command from a CPU 9 to apply analog sound volume adjustment through a prescribed combination in a prescribed dB step.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a volume adjustment device for a digital audio system, and more particularly to a volume adjustment device for a digital audio system that has a wide adjustment range and less distortion.

[Summary of the invention]

The present invention provides a volume adjustment device for a digital audio system, which includes a digital volume adjustment means, first and second analog volume adjustment means by switching between small attenuation steps and larger attenuation steps, and an instruction volume adjustment. By including a control section that selects a combination of the above-mentioned volume adjustment means according to the level, a volume adjustment device with a wide adjustment range and less distortion can be obtained.

[Conventional technology]

Compared to analog audio systems using AM-FM broadcasts, LP discs, tape recorders, etc.

Digital audio systems, such as PCM broadcasting, compact discs (CDs), and digital audio tapes (DATs), which have a much wider dynamic range and extremely less noise and distortion, are rapidly becoming popular.

Therefore, the quality of playback devices is required to be improved, and a volume adjustment device with a wide adjustment range and low distortion has become necessary as a part of the playback device.

Examples of conventional volume adjustment devices are shown in FIGS. 3 and 4.

FIG. 3 shows an example of a volume adjustment device using analog volume adjustment means, with digital input terminals 1. Digital-to-analog converter (hereinafter referred to as rDAcJ)2. Current-voltage converter (hereinafter referred to as rIVCJ)3. Feedback resistance R work. , sample and hold circuit (hereinafter referred to as rsHJ)4. Low pass filter (hereinafter referred to as rLPFJ)
5. It is composed of an attenuator 6 made of a variable resistor VR1 and an analog output terminal 7.

A digital audio signal input from digital input terminal 1 (for example, if a CD is used as the source program, 16 bits, dynamic range 96 dB) is converted to an analog current signal by DAC 2, and then converted to a current voltage determined by feedback resistor R1°. Based on the conversion ratio I
VC2; is converted into an analog voltage signal.

The extra signal components generated during this conversion process are SH4, LP
The signal is removed by F5 and input to the attenuator 6 as a normal analog audio signal.

When the value of the variable resistor VR is set, the analog audio signal is attenuated according to the instructed volume adjustment level and output from the analog output terminal 7.

FIG. 4 shows an example of a volume adjustment device using digital volume adjustment means, which includes a digital signal processing circuit (hereinafter referred to as rDsPJ) 8 inserted between the digital input terminal 1 and the DAC 2, as well as a control system using a microcomputer, etc. Department (
(hereinafter referred to as rCPUJ)9. Analog-digital converter (hereinafter referred to as rADCJ) 10 and variable resistor vR2
The structure is the same as the example shown in FIG. 3 except that the attenuator 6 is added and the attenuator 6 is removed, and the same parts are denoted by the same reference numerals and the explanation thereof will be omitted.

The variable resistor VR2 has one end connected to the power supply and the other end connected to the ground, and when set according to the instructed volume adjustment level, a corresponding analog DC level voltage is inputted to ADCl0. When the signal digitized by the ADC 10 is input to the CPU 9, the attenuation coefficient (K≦1) corresponding to the digital signal is read out from the memory and output to the DSP.
Sent to 8th.

On the other hand, a digital audio signal input from the digital input terminal 1 is multiplied by an attenuation coefficient K inside the DSP 8 to be adjusted to a predetermined volume level, and is input to the DAC 2.

After that, the same processing as in Fig. 3 is performed, and then
It is output from the analog output terminal 7 as an analog audio signal.

[Problem that the invention seeks to solve]

However, the analog sound volume adjustment means shown in FIG. 3 has a problem in that it tends to generate sliding noise and distortion after long-term use.

Furthermore, in the case of remote control, especially wireless remote control, a mechanical part such as a motor is required to adjust the variable resistor VR1, making fine adjustment even more difficult and causing problems such as noise generation from the mechanical part. will be added.

Furthermore, according to the digital volume adjustment means shown in Figure 4, there is no effect of stray capacitance, so the high frequency range is not lost, but as the amount of attenuation increases, the wide dynamic range is lost. There were problems such as distortion and noise becoming noticeable.

[Means for solving problems]

In order to solve the above problems, the present invention provides a volume adjustment device for a digital audio system, which includes a digital volume adjustment means, a first analog volume adjustment means by switching small attenuation steps, and the first analog volume adjustment means. The apparatus includes a second analog volume adjustment means that switches attenuation steps larger than that of the analog volume adjustment means, and a control section that selects a combination of the volume adjustment means according to the instructed volume adjustment level.

[Function] With the above configuration, the control section adjusts the volume by selectively combining the digital volume adjustment means and the first and second analog volume adjustment means according to the instructed volume adjustment level. Therefore, the maximum amount of attenuation of each volume adjusting means can be suppressed within a range that does not cause the above-mentioned problems, and the volume can be adjusted with a wide overall adjustment range and little distortion.

〔Example〕

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

FIG. 1 is a block diagram showing an example of a volume adjustment device embodying the present invention.
, ; feedback resistance R□. A resistor R is connected in parallel to 0.
A resistor R2 is added, and switches 11 and 12 for opening and closing the feedback circuits are provided to constitute the first analog sound volume adjustment means 13, and a resistor R2 is connected between the LPF 5 and the analog output terminal 7. R2□, R22
and resistance R2□.

Attenuator 1 which is a second analog volume adjustment means consisting of switches 21 and 22 that open and close between R2□ and ground.
4 was inserted. Note that the same parts as in FIG. 4 are designated by the same reference numerals, and the explanation thereof will be omitted.

To explain the operation of this embodiment, when the switches 11 and 12 are open, the feedback resistance of IVC3 is R1.
IVC; is set to a certain current-voltage conversion ratio, and the attenuation amount at that time is OdB.

When switch 11 is closed, the feedback resistor is Rl
o and R1 are connected in parallel, and the current-voltage conversion ratio is, for example, 1/
2, so the attenuation amount is 6 dB.

Furthermore, when switches 11 and 12 are closed, the feedback resistors R1o, R11, and R1 become parallel, and the current-voltage conversion ratio becomes, for example, 1/4, so the attenuation amount is 12d.
It becomes B.

On the other hand, in the attenuator 14, which is the second analog sound volume adjustment means, the amount of attenuation is OdB when the switches 21 and 22 are open.

When the switch 21 is closed, the lower end of R21 is grounded, and the output voltage is reduced to, for example, 1/4, that is, the amount of attenuation is reduced to 1.
2dB, and when switches 21 and 22 are closed, R2
1, R2° are grounded in parallel, and the output voltage is, for example, 1
/16, that is, the attenuation amount is set to 24 dB.

These switches 11.12 and 21.22
These are relays or electronic switches that are opened and closed by commands from 9. For example, by combining them as shown in the table below, the analog volume adjustment changes in 6 dB steps. (Open: ×, closed: O) Attenuation switch 11 12 2
1 220dB
X6dB OX X

For example, if the adjustment level step is 12 dB, C
The attenuation coefficients that the PU9 reads from the memory and sends to the DSP8 are 1 (Od B) and 0.79 (-2d B).

It is 0.63 (-4d B).

The analog DC level voltage corresponding to the instructed volume adjustment level outputted from the variable resistor vR2 is converted into a digital signal by ADClo according to the adjustment level step and adjustment range, and is input to the CPU 9. CPU9 has attenuation amount 3
Up to 6 dB, open and close each switch 11.12 and 21.22 as described above in steps of 6 dB.
Attenuation coefficient according to steps less than dB & send to DSP8.

FIG. 2 is a level diagram showing the method of adjusting the volume according to this embodiment, and the horizontal axis shows the instructed volume adjustment level. (A) shows the change in the level of the digital volume adjustment means (
B), (C), (D), and (E) are switches 11, 12, and 2 constituting the first and second analog volume adjustment means.
1.22 operation and the resulting change in level, (
F) is a combination of the above adjustment levels.

When the horizontal axis (instruction volume adjustment level) is OdB, CPU9
The attenuation coefficient sent from the switch is 1, and the switches 11, 12,
21.22 are all open. When the horizontal axis changes in 12 dB steps, K first changes to 0.79, the output of the DSP8 attenuates by 2 dB, and then becomes = 0.63. It is attenuated by 4dB.

When the horizontal axis reaches 16 dB, the switch 11 is closed as shown in (B) of the figure, and the output of the DSP 8 returns to O dB as shown in (A).

Next, -8 dB and -10 dB are obtained by changing the DSP8. When the horizontal axis reaches -12 dB, the switch 12 is also closed as shown in (C), and the DSP 8 changes to cover up to -16 dB as shown in (A).

When the horizontal axis reaches -18 dB, as shown in (C) and (D), switch 12 is opened and switch 21 is closed, covering up to -22 dB.

Similarly, all switches are closed when the voltage reaches -36 dB. When it exceeds -36 dB, the excess portion is adjusted by the DSP 8 as shown in (A).

The maximum attenuation amounts of the first and second analog sound volume adjustment means are -12 dB and -24 dB, respectively, which can be achieved without distortion or noise being a problem.

For example, even if the audio signal is 1/1000, that is, the amount of attenuation is 60 dB, the amount due to the digital volume adjustment means is 24 dB. For example, in the case of a CD, the dynamic range is still 72 dB, and distortion due to quantization is not a problem. No.

If all digital volume adjustment means were used, the dynamic range would be 36 dB, which is an extremely large difference.

Also, unlike the analog volume adjustment illustrated in Figure 3, even in the case of wireless remote control, it is only necessary to input the coded adjustment instructions directly to the CPU 9, and there are advantages such as no problems caused by the use of a motor, etc. There is.

In addition, in this example, the adjustment level step is 2 dB.
However, it goes without saying that the output of the DSP 8, that is, the digital sound volume adjustment means, allows the attenuation coefficient K to be adjusted as finely as desired.

Further, in this embodiment, the step of the first and second analog volume adjustment means is 6 dB, and each changes in three steps including OdB, but the step can be set arbitrarily or the number of changes can be increased or decreased. is also possible.

Furthermore, in the region where the attenuation amount is 42 dB or more, by appropriately selecting the attenuation coefficient K, the attenuation characteristic with respect to the change in the variable resistor VR can be set not only linearly but also arbitrarily.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a volume adjustment device with a wide adjustment range and less distortion in a digital audio system.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a level diagram for explaining the operation of the embodiment of Fig. 1, and Figs. 3 and 4 are block diagrams showing a conventional example. be. 2... Digital to analog converter (DAC) 3.
・Current voltage converter (IVC) 4...Sample hold circuit (SH) 5...Low pass filter (LPF) 8...Digital signal processing circuit (DSP) 9...Control unit (CPU)

Claims (1)

[Claims] 1. In a volume adjustment device for a digital audio system, a digital volume adjustment means, a first analog volume adjustment means by switching between small attenuation steps, and a second analog volume adjustment means by switching between attenuation steps larger than the first analog volume adjustment means. 1. A volume adjustment device for a digital audio system, comprising: analog volume adjustment means; and a control section that selects a combination of the volume adjustment means according to a commanded volume adjustment level.