JPH11122065A - Automatic equalizer of dsp constitution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute an automatic equalizer only the rough a DSP(digital signal processor) without the use of a microcomputer. SOLUTION: In this automatic equalizer for controlling the gain of an equalizer based on an input signal level, a digital signal processing (21) for monitoring the peak value of input audio signals in each prescribed period, the digital signal processing (22) for successively updating an equalizer coefficient value by the peak value and the digital signal processing (23) for executing an equalizing processing to the audio signals by using the equalizer coefficient value and outputting them are respectively performed by a DSP 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auto equalizer having a DSP structure, and more particularly to an auto equalizer for controlling a gain of an equalizer based on an input signal level.

[0002]

2. Description of the Related Art When an input signal level is low, low-frequency and high-frequency components are difficult to hear in terms of audibility. For this reason, there is an auto equalizer that increases the gain when the input signal level is low and restores the gain when the input signal level is high to prevent distortion, and uses a DSP (digital signal processor). There is one that is configured. FIG. 6 is a configuration diagram of an auto equalizer having such a DSP configuration.
Reference numeral 1 denotes a microcomputer, which includes an AD converter 1a for converting an input audio signal into a digital signal and a processor (CPU) 1b for calculating an equalizer coefficient value (EQ data) based on the level of the input audio signal. 2 is an AD converter for converting an input audio signal to digital, 3 is an EQ
A DSP (Digital Signal Processor) 4 performs an equalizing process on the audio signal using the data and outputs the resulting signal, and a DA converter 4 converts the DSP output into an analog signal.

[0003]

In such a conventional auto equalizer having a DSP configuration, the microcomputer 1 needs to detect the input signal level. Therefore, the microcomputer is A
The D converter 1a is required, and the D converter 1a overlaps with the A / D converter 2 for DSP, and the amount of hardware increases. Further, the microcomputer 1 calculates the EQ data by checking the constantly changing level of the music signal. For this reason, the microcomputer processing time must be devoted to the calculation of the EQ data and the communication with the DSP. In addition, in order to avoid a sudden change in gain, small data is required, which places a burden on the ROM capacity of the microcomputer. For this reason, if there is no room for the microcomputer to execute other control processing, it is necessary to provide a separate microcomputer, which increases the amount of hardware. From the above, the object of the present invention is:
An object of the present invention is to provide an automatic equalizer having a DSP configuration without using a microcomputer.

[0004]

According to the present invention, there is provided an auto-equalizer for controlling a gain of an equalizer based on an input signal level. (1) A digital equalizer for monitoring a level of an input audio signal every predetermined period. Signal processing, (2) digital signal processing for sequentially updating an equalizer coefficient value according to the audio signal level, and (3) digital signal processing for performing an equalizing process on an audio signal using the equalizer coefficient value and outputting the resulting signal to a DSP. This is achieved by a DSP-equipped auto-equalizer.

[0005]

There block diagram of the automatic equalizer DSP configuration of the embodiment of the invention Figure 1 the present invention, AD converter 11 for converting an input audio signal S _A to a digital signal x (n),
Reference numeral 12 denotes a DSP (digital signal processor), and reference numeral 13 denotes a DA converter that converts the DSP output signal y (n) into an analog signal. In the DSP, reference numeral 21 denotes a peak monitoring unit that monitors a peak value of the input audio signal x (n) every predetermined period (predetermined sampling number N), and 22 denotes an equalizer coefficient calculation that sequentially updates an equalizer coefficient (EQ data) based on the peak value. The unit 23 is an equalizer unit (EQ) that performs equalizing processing on the audio signal using the equalizer coefficient value and outputs the result.

[0006] The equalizer section 23 performs an IIR type digital filter process to obtain an audio signal x.
(n) is subjected to an equalizing process. In the block diagram of FIG. 1, DL is a sampling time delay unit, ML
Is a multiplication unit that multiplies the coefficients A to E, and AD is an addition unit that adds all the multiplier outputs. That is, the equalizer unit 23 equalizes the audio signal by the following equation: y (n) = Ax (n) + Bx (n-1) + Cx (n-2) + Dy (n-1) + Ey (n-2) (1) Perform processing.

[0007] The equalizer coefficient calculator 22 calculates equalizer coefficient values A to D based on the peak value of the input audio signal.
Is calculated and set in the equalizer unit 23. FIG. 2 is a diagram showing the relationship between the peak level and the equalizer gain G. When the peak level | x | of the input signal is 1, the equalizer gain G is 0 (dB), and when the peak level of the input signal is 0,
The equalizer gain G is +12 (dB), and when the peak level | x | of the input signal is in the range of 0 to 1, the equalizer gain G
Is determined by G = (1− | x |) ² · K (2). K is a constant, which will be described later. When the center frequency of the equalizer is 1 KHz and Q (sharp value) is 1, the coefficients A to E at the gains of 0 dB, +6 dB, and +12 dB are the values shown in FIG.
The frequency characteristics are as shown in FIG.

The target value of the gain G is determined by the equation (2). However, if this value is adopted suddenly, the EQ gain changes suddenly every N samplings, which is not preferable in terms of tone. Therefore, the EQ gain is smoothly increased or decreased by the attack / release processing. That is, the following equation G (n + 1) = G (n) + (GG (n)) × μ (3) is used to make the EQ gain gradually increase and decrease every sampling. In the equation (3), μ is a coefficient that determines an attack / release speed of 1 or less, G is a target gain, G
(n) is the current gain, and G (n + 1) is the gain at the next sampling time.

Referring to FIG. 3, when the equalizer gain G increases, the coefficient A increases, and the coefficient C decreases.
The increasing amount of the coefficient A and the decreasing amount of the coefficient C are equal.
The other coefficients B, D, and E do not change with the gain. Therefore, if the coefficients A and C are changed according to the peak level of the music signal (the other coefficients are constant), the gain G of the equalizer can be changed. That is, the equalizer coefficient calculator 22 may determine the coefficients A and C so that the gain changes according to the equations (2) and (3) according to the peak level of the music signal, and input the coefficients A and C to the equalizer 23. The constant K in the equation (2) is a difference between the minimum value and the maximum value of the coefficient A,
K = “CA5 _H ”.

In actual rewriting of the EQ coefficients, first, coefficient values A ₀ , B ₀ , C ₀ , D ₀ , and E ₀ with a gain of 0 dB are prepared as reference values. Then, the gain G (n + 1) obtained by the equation (3) for the coefficient values A ₀ and C ₀ for each sampling is expressed by the following equation: A = A ₀ + G (n + 1) (4) C = C ₀ −G (n + 1) The values of coefficients A and C are obtained by addition and subtraction according to (5).
The values of D and E are fixed at B ₀ , D ₀ and E ₀ , and these coefficient values are set in the equalizer unit 23. The equalizer 23 executes the operation of the expression (1) for each sampling, and outputs the obtained audio signal y (n).

FIG. 5 is a flow chart of an automatic equalizer digital signal processing by the DSP, where N is, for example, 2000. DS
P12 receives the input audio signal x (n) for each sampling and detects the peak level of the input signal x (n) for N samplings (step 101). Peak level ｜
When x | is obtained, the target gain G is calculated by the equation (2) (step 102), and then the attack / release calculation is performed by the equation (3) to calculate the gain G (n + 1) at the next sampling time. (Step 103). Gain G (n + 1)
Is obtained, the values of the coefficients A and C are calculated by the equations (4) and (5) (step 104), and the values of the equalizer coefficients A to E are rewritten. An arithmetic operation is performed to output an audio signal y (n) obtained by performing an equalizer process (step 105).

Next, the magnitude of the previous peak level | x | and the current sampling value | x (n) | are compared. If the current sampling value | x (n) | If the previous peak level | x | is large, the peak level is not updated (step 1).
06). Thereafter, n (the initial value is 0) is incremented (step 107), and it is checked whether or not n = N (step 108). If n <N, the processing after step 103 is repeated, and n = n If N, the process returns to step 101 and the subsequent processing is repeated. As described above, an auto equalizer can be configured using only a DSP without using a microcomputer. Therefore, an increase in the amount of hardware can be prevented, and the gain can be smoothly increased / decreased at each sampling by the attack / release processing, so that the sound changes naturally. In the above description, the auto equalizer control is performed based on the peak level. However, the auto equalizer control can be performed based on the average level and the like. As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[0013]

As described above, according to the present invention, in an automatic equalizer for controlling the gain of an equalizer based on an input signal level, digital signal processing for monitoring the level of an input audio signal every predetermined period, and an equalizer based on the audio signal level Digital signal processing for sequentially updating coefficient values, digital signal processing for performing equalizing processing on an audio signal using the equalizer coefficient values and outputting the resulting signal,
Since each processing is performed by the DSP, an auto equalizer can be configured only by the DSP without using a microcomputer.
Therefore, an increase in the amount of hardware can be prevented, and furthermore, the gain can be smoothly increased / decreased at each sampling by the attack / release processing, and the change in sound can be made natural.

[Brief description of the drawings]

FIG. 1 is an auto equalizer having a DSP configuration according to the present invention.

FIG. 2 is a relationship curve between an input signal peak level and an EQ gain.

FIG. 3 is an explanatory diagram of a relationship between a gain and each coefficient value.

FIG. 4 is a frequency characteristic diagram.

FIG. 5 is a digital signal processing flow of a DSP auto equalizer.

FIG. 6 shows an equalizer having a conventional DSP configuration.

[Explanation of symbols]

 11. AD conversion circuit 12. DSP (Digital Signal Processor) 13. DA converter 21. Peak monitoring unit 22. Equalizer coefficient calculation unit 23. Equalizer unit (EQ)

Claims (1)

[Claims] 1. An automatic equalizer for controlling a gain of an equalizer based on an input signal level, a digital signal processing for monitoring a level of an input audio signal every predetermined period, and a digital for sequentially updating an equalizer coefficient value based on the audio signal level. An auto equalizer having a DSP configuration, wherein the DSP performs digital signal processing for performing signal processing and equalizing processing on an audio signal using the equalizer coefficient value and outputting the resulting signal.