JPS63189005A - Sound volume controller - Google Patents

Abstract

PURPOSE:To prevent deterioration in tone quality when sound is low, by setting the output voltage of a D/A converter controlled by a bus line as the reference voltage of the D/A converter. CONSTITUTION:The D/A converter 1 is controlled by the bus line. The reference voltage is applied on the D/A converter 2 via an RC filter 3. A sound output level that is the conversion output of the D/A converter 2 changes almost in proportion to the reference voltage. Meanwhile, a sound volume data is sent to the D/A converter 1 via the bus line, and the converter 1 generates corresponding DC voltage by the RC filter 3. The output voltage of the filter 3 can perform sound volume control by setting it as the reference voltage of the converter 2. Since the converter 1 generates only a sound volume control voltage, it is enough to prepare the one operated at low conversion speed, and the converter is constituted of the one of simple type such as a PWM type converter, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a volume control device for digital processing of audio signals.

(Prior Art) In recent years, attempts have been made to introduce a volume control device as a part of digital signal processing together with sound quality control, balance control, etc. A conventional volume device will be explained based on FIG. In the figure, 11 is a multiplier, and 12 is a D/A converter. One input of the multiplier 11 is an audio signal consisting of m bits;
The other is a coefficient value consisting of n bits. If the multiplier 11 normalizes the maximum values of the two inputs to ±1, the output of the multiplier 11 will take a value from 0 to ±1 depending on the multiplied coefficient value. By D/A converting the output of the multiplier 11, an audio signal output whose amplitude is controlled by the coefficient value can be obtained, and the multiplier 11 functions as a volume control device.

(Problem to be solved by the invention) In general, in digital signal processing that handles audio signals, the dynamic range of a D/A converter is much smaller than m bits, for example, a D/A converter is 90 dB (about 15 bits).
, when the data length m of the audio signal is 24 bits (equivalent to 144 dB), there is little characteristic deterioration in digital signal processing. If you reduce the volume with such a volume control device,
Depending on the characteristics of the power amplifier and speakers used, just before the sound becomes audible, you will hear about 2 to 4 bits of sound, and the quantization noise will hit your ears, resulting in considerably poor quality audio. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a volume control device that eliminates the drawbacks of the prior art and can reduce deterioration in audio quality even when the volume is reduced.

(Means for Solving the Problems) The volume control device of the present invention includes a D/A converter controlled by a bus line, and a D/A converter for an audio signal having the output voltage of the D/A converter as a reference voltage. A converter.

(Function) With the above configuration, the present invention allows a constant signal to be applied to the audio signal D/A converter regardless of the volume, and the audio control is performed using the D/A converter controlled by the bus line.
Since this is done using the output voltage of the converter, there is little deterioration in the characteristics of the audio signal, especially when the volume is low.

(Example) An embodiment of the present invention will be described based on FIG.

FIG. 1 is a block diagram of a volume control device according to the present invention. In the figure, 1 is a D/A converter controlled by bus line;
2 is an audio signal D/A converter, 3 is an RC filter, and 4 is a reference voltage line applied to the D/A converter 2.

The operation of the volume control device configured as described above will be explained.

The audio output level, which is the converted output of the D/A converter 2, changes approximately in proportion to the reference voltage. On the other hand, volume data is sent to the D/A converter 1 through the bus line, and the D/A converter 1 generates a corresponding DC voltage using the RC filter 3. By using the output voltage of the RC filter 3 as the reference voltage of the D/A converter 2, the volume can be controlled.

Since the D/A converter 1 only generates the volume control voltage,
The conversion speed is low and can be configured with a simple one such as a PWM (pulse width modulation) type.

(Effects of the Invention) According to the present invention, a D/A converter controlled by a bus line and an audio signal D/A converter having the output voltage of this D/A converter as a reference voltage are provided. This makes it possible to prevent deterioration of sound quality even when the sound is low, and has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a volume control device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional volume control device. 1...D/A converter, 2...D/A converter,
3...RC filter, 4...Reference voltage line. Patent Applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 3... RC filter 4... Waxing material Figure 2 4 No. 1 ζ 1);

Claims (1)

[Claims] a D/A converter controlled by a bus line;
D/A of audio signal with output voltage of A converter as reference voltage
A volume control device characterized by comprising a converter.