JPH01284117A - Audio signal processor - Google Patents

Abstract

PURPOSE:To suppress the fall of a dynamic range and the deterioration of S/N in a digital part, and to improve quality by controlling a level at an analog area according to the level of an audio signal to be inputted at the time of the occurrence of over-flow. CONSTITUTION:The audio signal to be inputted is converted into a digital signal by an analog-digital converter(ADC) 1, and inputted to a digital signal processor(DSP) 2. When the signal of the level higher than the prescribed input level is inputted, a level detector 7 controls an attenuator(ATT) 4, and since it attenuates the level to be inputted to a DSP operating part 5, the DSP operating part 5 can perform operational processing without causing the over-flow. Besides, the level attenuated by ATT 4 is corrected by a gain amplifier 6 of an analog part. Thus, the dynamic range can be expanded, and simultaneously, the high quality audio digital signal processing of good S/N comes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an audio signal processing device using a digital signal processor.

Conventional technology In recent years, digital signal processors (hereinafter abbreviated as DSP) have been rapidly developing due to advances in LSI technology, and various companies have developed various one-chip DSPs.
Audio equipment using DSP is about to be developed. When processing audio signals using a DSP, the basic configuration is shown in FIG.

In Figure 3, 1 is an analog-digital converter (
Hereinafter, it will be abbreviated as ADC. ), 2 is a DSP, and 3 is a digital-to-analog converter (hereinafter abbreviated as DAC).

The operation of the audio signal processing device configured as described above will be explained.

The analog signal is converted into a digital signal by ADCl, subjected to the desired arithmetic processing by DSP2, and converted to DA
It becomes an analog signal through C3.

Problems to be Solved by the Invention However, with the above configuration, overflow may occur depending on the processing content of the DSP 3. For example, if the digital data input to the DSF3 takes the maximum value and the DSF3 performs further amplification operation, as shown in Figure 4, when an overflow occurs, the audio signal output becomes a limiter operation and loses continuity. Now.

Therefore, conventionally, in order to prevent the above-mentioned overflow,
Although the input level was pre-attenuated, this leads to signal attenuation, i.e., the signal-to-noise ratio (S
/N ratio). As described above, there have been problems such as a limited dynamic range due to DSP processing and deterioration of the S/N ratio.

In view of the above problems, the present invention controls the level in the analog domain when an overflow occurs according to the input audio signal level, suppresses the decline in dynamic range and S/N ratio in the digital section, and improves quality. The present invention provides a high quality audio signal processing device.

Means for Solving the Problems To achieve this object, the audio signal processing device of the present invention includes an A/D converter that converts an analog audio signal into a digital audio signal, and an attenuation degree of the input level of the digital signal. An attenuator for switching the amplification level, a digital signal processing section that receives the output of the attenuator as input, a D/A converter, and an amplifier for switching the amplification level are provided in series, and the input level is detected in parallel with the attenuator. and a level detector for controlling the attenuator and amplifier.

According to the present invention, the level detector detects the input level with the above-described configuration, and when a predetermined input level or higher is input, the ATT is controlled and the level input to the DSP calculation section is attenuated. This allows the DSP calculation section to perform calculation processing without overflowing, and by correcting the level attenuated by the ATT with the gain amplifier, which is an analog section with a relatively large degree of freedom, the continuous audio signal You can maintain your sexuality.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an audio signal processing device in an embodiment of the present invention.

In Figure 1, 1 is ADC, 2 is DSF, 3 is DAC
14 is an attenuator (ATT), 6 is a DSP calculation section, θ is a gain amplifier, and 7 is a level detector.

FIG. 2 is a waveform diagram showing the operation of each part in FIG. 1. a
b is the input analog input waveform, b is the output waveform of the level detector 7, C is the DAC 3 output waveform, and d is the gain amplifier output waveform which is the final output.

The operation of the audio signal processing device of this embodiment will be described below.

In FIG. 1, the input audio signal is
1 is converted into a digital signal and input to the DSP2. The input digital signal passes through ATT4 and D
The SP calculation unit 5 performs predetermined calculation processing and the DSF2
The digital signal is output from the DAC 3 and converted into an analog signal by the DAC 3. A level detector 7 provided in parallel with the ATT3 detects the level input to the DSF2, and a threshold value is set in advance below a level value at which overflow occurs.

When the input level is below the threshold value, the level detector 7 outputs 0, and controls the attenuation of the ATT 4 to 0 and the amplification of the gain amplifier 6 to 1. In other words, the operation is similar to the conventional one shown in FIG. When the next input level is equal to or higher than the threshold value, the level detector 7 outputs 1 and attenuates the digital input by a predetermined coefficient so that the attenuation degree of the ATT 4 becomes 1/α. Based on the attenuated digital input, the DSP calculation section 6 performs predetermined calculation processing and outputs the result. Then, the DAC 3 converts the υ digital signal into an analog signal. The output of the level detector 7 also controls the gain amplifier 6 at the same time, switches the amplification degree of the gain amplifier 6 to d, and operates to correct and amplify the level attenuated by the ATT 4. In other words, as shown in the operation waveform diagram of each part in Figure 2, when the waveform at point b is level ○, there is no cause for overflow occurrence, so it is normal operation, and when the waveform at point b is level 10, overflow has occurred. ATT is expected only in this section.
4, the level is attenuated and calculated to obtain the waveform C as the output of the DAC 3, which is corrected and amplified by the gain amplifier 6 to obtain the final output waveform shown in d.

As shown in this embodiment, by detecting the input level that is the cause of the overflow, the overflow generated inside the DSP is removed and corrected by the analog section at the subsequent stage, thereby making it possible to maintain signal continuity.

Effects of the Invention The present invention focuses on the overflow phenomenon of digital signal processing, and uses an analog signal processing unit to compensate for the data width constraints that are inevitable with digital signals, thereby expanding the dynamic range and reducing the input level. This is an audio signal processing device that enables high-quality audio digital signal processing with a good S/N ratio without having to set it small due to overflow.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an audio signal processing device in one embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of each part in FIG. 1, and FIG. 3 is the configuration of a conventional audio signal processing device. FIG. 4 is a waveform diagram showing the operation of each part in FIG. 3. 1...ADC, 2...DSP, 3...
...DAC. 4...ATT, 6...DSP calculation section,
6...gain amplifier, 7...level detector. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure - Unpublished

Claims (1)

[Claims] An A/D converter that converts an analog audio signal into a digital signal, an attenuator that switches the degree of attenuation of the input level of the digital signal, a digital signal processing unit that receives the output of the attenuator as an input, and converts the digital signal into an analog signal. A D/A converter for conversion and an amplifier for switching the amplification degree are provided in series, and a level detector is provided in parallel with the attenuator for detecting the input level and controlling the attenuator and the amplifier. An audio signal processing device characterized in that when the level increases, the level is attenuated by the attenuator, and the attenuation is corrected and amplified by the amplifier.