JPH07221571A - Digital tone controller - Google Patents

Abstract

PURPOSE:To implement proper amplification control free from digital clipping by minimizing the reduction of a dynamic range. CONSTITUTION:Filters 11a, 11b are used to extract a specific frequency band component of an input signal and variable amplifiers 12a, 12b amplify the extracted component at a multiple of K. On the other hand, attenuators 10a, 10b attenuate the input signal by a prescribed value; and adders 13a, 13b are used to add the attenuated signal and the amplified signal to the specific frequency band component respectively. The digital audio signal after the end of addition is fed to a level discrimination section 14, and an amplified quantity calculation section 15 increases/decreases the coefficient K with a negative constant A and a positive constant B based on the result of level discrimination. In this case, the controller is provided with a control means that limits the coefficient K within a range of a maximum value Kmax or below and a minimum value Kmin or over, and the added value to the adders 13a, 13b is changed depending on the coefficient K to adjust the amplified quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tone control device for implementing tone control processing in digital signal processing in various audio devices.

[0002]

2. Description of the Related Art FIG. 3 shows the configuration of a conventional digital tone control device. In FIG. 3, this example is composed of functional processing in a digital signal processor (hereinafter abbreviated as DSP), and attenuators 30a and 30b to which digital audio input signals of right (R) and left (L) channels are supplied, and a specific frequency band. A filter (hereinafter referred to as a tone filter) 31a for increasing or decreasing the level of
31b is provided.

The operation of this conventional configuration will be described. Before the input signals are enhanced by the tone filters 31a, 31b, an amount equal to the maximum value of the enhancement amount is attenuated by the attenuators 31a, 30b as a clip margin.

For example, when the tone filters 31a and 31b are used to enhance the maximum +12 dB, the input signals are attenuated by 12 dB in the attenuators 30a and 30b.

[0005]

However, in the above-described conventional tone control device, when a full-bit signal (hereinafter, referred to as maximum input) is input in the DSP, the tone filter performs the enhancement process. It becomes a digital clip state, resulting in the output of noise and abnormal noise. This is because overflow or underflow occurs in the digital signal processing in the DSP, a folded waveform occurs, and the overflow correction processing fixes the calculated value to the maximum value or the minimum value. Therefore, do not exceed the maximum input to the DSP,
Whatever input signal is input, if it is enhanced by the tone filter, a method for preventing this digital clipping is needed.

Further, the digital dynamic range is determined by the number of bits of the signal, and in the conventional example, the effective bit is reduced and attenuated by attenuating an amount equal to the maximum value of the enhancement amount of the tone filter. However, there was a drawback that the dynamic range was reduced.

The present invention solves such a conventional problem, and provides an excellent digital tone control device capable of suppressing the reduction of the dynamic range to the minimum and performing the proper enhancement without the digital clip. To aim.

[0008]

In order to achieve the above object, the invention according to claim 1 provides a filter for extracting a specific frequency band component of a digital audio signal, and a coefficient K to the signal extracted by the filter. Multiplication processing means for multiplying, addition means for adding a signal from the multiplication processing means to an input signal, level determination means for determining whether or not the level of the signal from the addition means is equal to or more than a threshold value, and the level determination means. At a level above the threshold, the first constant adding means for adding a negative constant A to the coefficient K, and the coefficient K when the level determining means detects a level below the threshold. Is provided with a second constant adding means for adding a positive constant B and limiting means for limiting the value of the coefficient K to the maximum value K _max or less and K _min or more, and the addition amount is changed by the coefficient K to enhance the value. amount It is characterized in that the adjusting.

The invention according to claim 2 is characterized in that B <-A in claim 1.

The invention according to claim 3 is characterized in that an attenuator that attenuates the input signal by a predetermined amount is provided.

[0011]

According to the first aspect of the present invention, a signal in a specific frequency band is added to an input signal to enhance the signal, the level of the output signal is detected, and the addition amount is appropriately adjusted by feedback control. The amount of enhancement can be adjusted within a range that does not cause clipping. As a result, when the input signal is at a low level where digital clipping does not occur even when the input signal is enhanced, the enhancement can be performed without attenuating the input signal. Further, when the input signal is at a large level at which digital clipping occurs when the enhancement is performed, it is possible to control the enhancement amount and perform the enhancement within the range where the digital clipping does not occur.

As described above, since the strengthening process is performed without attenuating the input signal, it is possible to perform the proper strengthening without reducing the dynamic range and without the digital clip.

In the invention according to claim 2, the constants A and B have the relationship of B <-A in the above structure, so that the enhancement amount can be adjusted without a feeling of discomfort.

According to a third aspect of the invention, in addition to the above configuration,
By providing the attenuator that attenuates the input signal by a certain amount, it becomes possible to guarantee the minimum amount of enhancement equal to the amount attenuated by the attenuator.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a digital tone control device of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of the embodiment. In FIG. 1, this example consists of functional processing in the DSP,
Attenuators 10a and 10b for attenuating digital audio input signals of right (R) and left (L) channels
And filters 11a, 11 for extracting the specific frequency band component
b, the variable amplifiers 12a and 12b, and the adders 13a and 1
3b, a level determination unit 14, and an enhancement amount calculation unit 15 are included.

Next, the operation of the configuration of this embodiment will be described. In FIG. 1, filters 11a and 11b are provided.
The specific frequency band component is extracted with and variable amplifiers 12a, 12
Amplify K times in b. On the other hand, attenuators 10a, 10
b attenuates the amplitude of the input signal by 6 dB, and the adder 13a,
In 13b, it is added to the specific frequency band component. The digital audio signal after the addition process is supplied to the level determination unit 14, and the enhancement amount calculation unit 15 is controlled according to the result of the level determination.

Here, the maximum value K _max of the coefficient K and the amount of enhancement X
The relationship of can be expressed by the following equation.

[0019]

[Equation 1]

FIG. 2 is a flow chart relating to the processing procedure of the level judgment to enhancement amount calculation section. The parameter set here is only K _max .

In the level determining step (denoted by S in the drawing) 1, it is determined whether or not the signal levels of the right (R) and left (L) channels are above a threshold value. In this embodiment, the absolute values of the right (R) and left (L) signals are taken, and it is determined whether or not the maximum bit excluding either sign bit is 1.
That is, if the maximum value of the digital signal is 0 dB, it is -6
It is determined whether it is equal to or higher than dB. If the maximum bit = 1 is not detected in step 1, the process proceeds to step 2 and the coefficient K is K.
Only when it is smaller than _max , the positive constant B is added to the coefficient K in step 3. When the maximum bit = 1 is detected in step 1, it is determined in step 4 whether K _max is larger than 0.5. That is, it is determined whether or not the enhancement exceeding +6 dB is performed. If No in step 4, step 5
In step 6, K _max is substituted into K _min , and in the case of Yes, in step 6, 0.5 is substituted into K _min . If No in step 4,
By setting K _min = K _max , the coefficient K is converged to K _max . If Yes in step 4, by setting K _min = 0.5, the coefficient K is maintained at 0.5 or more + 6d
B enhancement will be guaranteed. In step 7, the negative constant A is added to the coefficient K in step 8 only when the coefficient K is larger than K _min .

[0022] As described above, the coefficient limiting step 2,7, feedback range values of the coefficient K is varied between a maximum value K _{ma x} and the minimum value K _min, enhancing amount of variation in the factor K Automatically adjusted.

The value of the constant A in this case determines the shortest time At for the coefficient K to change from the maximum value K _max to the minimum value K _min . Further, the value of the constant B determines the shortest time Lt from the minimum value K _min to the maximum value K _max of the coefficient K. The minimum times At and Lt can be expressed by the following equations. Here, fs is a sampling frequency.

[0024]

[Equation 2]

[0025]

[Equation 3]

At this time, by providing the relationship of B <-A, it is possible to adjust the amount of enhancement without a feeling of strangeness.

Further, by providing an attenuator that attenuates the input signal by a certain amount, it is possible to guarantee the amount of enhancement by the amount of attenuation.

[0028]

As is apparent from the above description, according to the invention of claim 1 of the digital tone control apparatus of the present invention, a signal of a specific frequency band is extracted from an input signal and added to the input signal. Since the level of the output signal is boosted and the amount of addition is adjusted properly by feedback control, if the input signal is at a low level at which digital clipping does not occur even when boosted, the input signal is not attenuated. Both can be augmented. Further, when the input signal is at a large level at which digital clipping occurs when the enhancement is performed, it is possible to control the enhancement amount and perform the enhancement within the range where the digital clipping does not occur.

As described above, since the strengthening process is performed without attenuating the input signal, it is possible to perform the proper strengthening without reducing the dynamic range and without the digital clip.

According to a second aspect of the invention, in the above configuration,
By providing the relationship of B <-A, it is possible to adjust the amount of enhancement without a sense of discomfort.

According to the invention of claim 3, in addition to the above configuration, by providing an attenuator for a certain amount of attenuation of the input signal, it becomes possible to guarantee the minimum amount of enhancement equal to the amount of attenuation here.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a digital tone control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation processing procedure in the embodiment.

FIG. 3 is a block diagram showing the configuration of a conventional digital tone control device.

[Explanation of symbols]

 10a, 10b Attenuators 11a, 11b Filters 12a, 12b Variable amplifiers 13a, 13b Adder 14 Level determination unit 15 Enhancement amount calculation unit 30a, 30b Attenuators 31a, 31b Tone filter

Claims (3)

[Claims] 1. A filter for extracting a specific frequency band component of a digital audio input signal, multiplication processing means for multiplying the signal extracted by the filter by a coefficient K, and a signal from the multiplication processing means is added to the input signal. Addition means, level determination means for determining whether or not the level of the signal from the addition means is above a threshold value, and if the level determination means detects a level above the threshold value, the coefficient K is negative. First constant adding means for adding a constant A, second constant adding means for adding a positive constant B to the coefficient K when the level determining means detects a level less than a threshold value, and the coefficient and a limiting means for the value of K is limited more than or less and K _min maximum value K _max, digital tone control apparatus characterized by adjusting the enhancing amount by changing the addition amount by a factor K 2. The relationship between the positive constant B and the negative constant A is B <
2. The digital tone control device according to claim 1, wherein the digital tone control device is A. 3. The digital tone control apparatus according to claim 1, further comprising an attenuator that attenuates an input signal by a predetermined amount.