JPH0819088A - Sound processing method - Google Patents

Abstract

PURPOSE:To simply eliminate a noise sound component such as howling sound by emphasizing the noise sound component and revising a filter coefficient of an equalizer into a coefficient representing a notch filter characteristic so as to eliminate the noise sound component. CONSTITUTION:Coefficients a0-a2, b1, b2 set to coefficient multipliers 24-26, 30, 31 of a digital filter are changed under the control of a central processing unit 14 to emphasize of a prescribed band as a parametric equalizer and to attenuate a prescribed band as a notch filter. In this case, secondary IIR digital filters connected in 31-stages are used to form the parametric equalizer and the notch filter in which the center frequency changes in 31-stages at an interval of 1/3 octave. Then the gain of the equalizer at a prescribed frequency is increased by shifting the center frequency so as to emphasize the noise sound component and the filter coefficients of the equalizer are revised into coefficients representing the notch filter characteristic to eliminate the noise sound component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound processing method suitable for applying sound picked up by a microphone in a hall or the like to a speaker.

[0002]

2. Description of the Related Art Conventionally, when a speaker picks up a sound picked up by a microphone in a hall or the like, the sound characteristics of the reproduced sound signal are corrected by using an equalizer (equalizer). There is. As an acoustic correction using this equalizer, for example, it may be used to suppress a phenomenon called howling in which a sound reproduced from a speaker is input to a microphone and fed back, and an oscillating sound is output from the speaker. .

FIG. 11 is a diagram showing a conventional circuit configuration for suppressing the howling, in which 1 is a microphone,
The acoustic signal picked up by the microphone 1 is supplied to the mixing console 2. The mixing console 2 performs a synthesis process with other audio signals. Then, the acoustic signal processed and output by the mixing console 2 is supplied to the parametric equalizer 5. The parametric equalizer 5 performs a process of increasing and emphasizing a gain in a predetermined frequency band.
The frequency band for increasing the gain can be changed from the high frequency band to the low frequency band by operating the operation unit provided in the.

Then, the acoustic signal output from the equalizer 5 is supplied to the notch filter 6. This notch filter 6
Is a filter for performing processing of attenuating the frequency band set by the operation of the operation unit provided in the filter 6. Then, the output of the notch filter 6 is supplied to the speaker 4 via the output amplifier 3, and the sound is emitted with a predetermined output.

The process of suppressing howling by this circuit will be described. First, in the initial state, the notch filter 6 is not attenuated. Then, the frequency band in which the gain is increased by the parametric equalizer 5 is gradually changed from a high band to a low band, and it is confirmed whether the sound output from the speaker 4 includes an oscillating sound (howling sound). Then, when any one of the bands is emphasized and the oscillation sound is large and is output from the speaker 4, it is determined that there is a howling sound in this frequency band.

When the frequency band in which the howling sound is present is confirmed, the specific frequency band in the parametric equalizer 5 is stopped from being emphasized to have a flat frequency characteristic, and the frequency band in which the howling sound is present is generated by the notch filter 6. Is performed.

By doing so, it is possible to prevent a howling sound when the sound is reproduced in a space such as a hall.

When the gain is increased by the parametric equalizer 5, its frequency band is set to a relatively wide frequency band so that howling sounds can be easily detected. On the other hand, when the howling sound is removed by the notch filter 6, the frequency band to be attenuated is set to be relatively narrow so that only the frequency at which the howling sound is generated is removed and the influence on other reproduced sounds is affected. I try to minimize it.

[0009]

However, in such conventional processing, there are two steps, that is, the processing of detecting the frequency band of the howling sound using the parametric equalizer and the processing of removing the detected band by the notch filter. Processing is required, both the parametric equalizer and the notch filter are required to be operated, and the operation is troublesome. Also, the configuration requires a two-stage processing circuit including the parametric equalizer and the notch filter, which makes the configuration complicated. There was some inconvenience.

In view of the above points, the present invention has an object of providing an acoustic processing method capable of easily removing an abnormal sound component such as a howling sound.

[0011]

According to the present invention, for example, as shown in FIG. 1, in a sound processing method for outputting an input sound signal from a speaker via an equalizer 10, a process of increasing a gain of a predetermined frequency of the equalizer. By moving the center frequency to emphasize the abnormal sound component,
The filter coefficient of the equalizer is changed to a coefficient showing a notch filter characteristic to remove an abnormal sound component.

Further, in this case, the acoustic signal picked up by the microphone is supplied to the equalizer.

Further, in this case, the abnormal sound component is a howling sound.

[0014]

According to the present invention, the abnormal sound component can be removed by the processing using only the equalizer.

In this case, the howling sound can be easily removed by performing the howling sound removing process.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 10, parts corresponding to those of FIG. 11 described as a conventional example are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a diagram showing the overall configuration of a processing system to which the sound reproducing method of this example is applied. In this example, the acoustic signal picked up by the microphone 1 is supplied to the equalizing device 10 via the mixing console 2. To do. The equalizer 10 converts the supplied audio signal into digital audio data by an analog / digital converter 11 and supplies the converted digital audio data to a digital audio data processing circuit 12 called DSP. The digital audio data processing circuit 12 is a circuit for performing gain adjustment, delay processing, etc. for each band of audio data supplied by digital processing. These circuits are controlled by a central control unit (CPU) 14 composed of a microcomputer. Is processed. In this case, the gain adjustment is processed by the 31-stage cascade connection circuit of the second-order IIR type digital filter.

Then, the audio data processed by the digital audio data processing circuit 12 is supplied to the digital / analog converter 13 and converted into an analog audio signal. Then, the converted acoustic signal is supplied to the output amplifier 3 as an output of the equalizer 10, and the acoustic signal amplified by the output amplifier 3 is supplied to the speaker 4 to emit a sound.

In the equalizer 10 of this embodiment, the operation keys 15 and the display panel 16 are connected to the central controller 14, and the operation state of the digital audio data processing circuit 12 is set according to the operation of the operation keys 15. At the same time, the setting status of the processing status is displayed on the display panel 16.

FIG. 2 shows the configuration of a second-order IIR type digital filter which performs gain adjustment and the like in each frequency band in the digital audio data processing circuit 12. Figure 2
21 indicates an audio data input terminal,
The audio data obtained at the input terminal 21 is delayed by the delay circuits 22 and 23 by one sample timing, and the undelayed signal, the signal delayed by one sample, and the signal delayed by two samples are respectively multiplied by the coefficient multiplier 24, 25,
26, and the coefficients a0, a1, and a2 are respectively multiplied, and the multiplication signals are added by the adder 27. Then, the addition output of the adder 27 is supplied to the delay circuits 28 and 29 to delay it by one sample, and the addition output is delayed by one sample and the signal delayed by two samples to obtain coefficient multipliers 30 and 31, respectively. To the coefficients b1 and b2, respectively.
Is multiplied, the multiplication signal is returned to the adder 27, and is added together with the other signals described above. Then, the addition output of the adder 27 is supplied to the output terminal 32.

In this way, a second-order IIR type digital filter is constructed. In the case of this example, the coefficient multipliers 24, 25, 26, 30,
The coefficients a0, a1, a2, b1, b2 set to 31 are
By changing the control by the central controller 14, a predetermined band as a parametric equalizer can be emphasized and a predetermined band as a notch filter can be attenuated. Here, in the case of this example, a secondary IIR connected in 31 stages
Type digital filter is used to construct a parametric equalizer and a notch filter whose center frequency changes in 31 steps at 1/3 octave intervals.

The display of the adjustment state on the display panel 16 is as shown in FIG. 3 when a predetermined band is emphasized as a parametric equalizer under the control of the central control unit 14, and a predetermined band is obtained as a notch filter. In the case of attenuating, the state becomes as shown in FIG. That is, in the case of this example, the display unit 41 on the display panel 16 showing that it is operating as a parametric equalizer.
, A display section 42 that indicates that the filter is operating as a notch filter, a display section 43 that indicates that the bypass operation is being performed without operating any filter, and a display section 44 that displays the center frequency of the adjusted band. And its gain display section 45
And a display unit 46 for adjusting the sharpness Q of the band to be adjusted. Then, when operating as a parametric equalizer, as shown in FIG. 3, the corresponding display is performed on the display unit 41, and the display units 44, 45, 46 display according to the current adjustment state. Further, when operating as a notch filter, as shown in FIG.
A display according to the current adjustment state is made at 46 (display unit 45
Does not display the gain in).

Here, the transfer function H _MP2 (Z) when operating as a parametric equalizer using the digital filter as in this example is shown in the following equation.

[0024]

[Equation 1]

The transfer function H _BE2 (Z) when operating as a notch filter is shown in the following equation.

[0026]

[Equation 2]

To explain the characteristics when operated in this way, first, when operating as a parametric equalizer, for example, one of the characteristic curves shown in FIG. 5 can be selected. In this FIG. 5, the gain to be emphasized is 1
2 dB is shown, and the case where the center frequency is changed in 10 steps is shown. The gain to be emphasized can be freely set like each characteristic curve shown in FIG.

When operating as a notch filter, for example, one of the characteristic curves shown in FIG. 7 can be selected. Here, the case where the center frequency is changed in 10 steps is shown. Then, the sharpness Q can be freely set as in the characteristic curves shown in FIG. The gain to be attenuated is −∞.

Next, the processing of this example performed using the circuit configured as described above will be described with reference to the flowchart of FIG. 9. First, the equalizer is set to operate as a parametric equalizer (PEQ). And gain = + 15 dB, sharpness Q = 50.0
Is set as a characteristic (step 101). At this time, only the characteristics are set, and the equalizer is not actually operated. Then, the center frequency f to be emphasized
₀ is set near the howling frequency (step 102).

Then, it is operated as an equalizer (step 103), and the center frequency f ₀ to be emphasized is moved by one step (step 104). Here, it is determined whether the howling frequency is detected in the emphasized band (step 105). That is, for example, by determining the sound reproduced from the speaker, it is determined whether or not the oscillating sound is audible.

If the howling frequency is not detected here, it is determined whether or not the howling sound pressure is high (step 106). When the sound pressure of the howling is high, the gain is reduced to the minimum level at which the howling occurs (step 107). Then, next, returning to step 104, the center frequency f ₀ to be emphasized is moved by one step.

When the howling frequency is detected in step 108, the characteristic of the equalizer is changed to a notch filter while the center frequency f ₀ is fixed, and the howling frequency is removed (step). 108). Then, the howling frequency is continuously removed until the reproduction by the reproduction system is completed. However, when the howling frequency is changed, the processing is repeated up to this point to detect and remove another howling frequency.

[0033] To describe the characteristic diagram of FIG. 10 to process up to this point, for example, as shown in A of FIG. 10, the frequency f ₁
Howling is occurring. Then, as a parametric equalizer, as shown in B of FIG. 10, it is assumed that the vicinity of the center frequency f ₀ is gain enhanced by +15 dB. Then, when the frequency to be emphasized is gradually brought closer to the howling frequency and the frequencies are matched as shown in C of FIG. 10, the level of the oscillation sound generated by the howling becomes high. At this time, with the center frequency f ₀ fixed,
As shown in D of FIG. 10, the gain is set to −∞, which shows the characteristic of the notch filter, and the oscillating sound caused by howling is removed.

By performing the processing as described above, howling can be easily removed only by using the equalizing device 10 of the present example. That is, after detecting the center frequency of howling, it is sufficient to switch the operating state of the equalizer 10 from the parametric equalizer to the notch filter with the center frequency fixed, and howling can be easily removed. In this case, switching from the parametric equalizer to the notch filter simply changes the coefficient to be multiplied by the digital filter in terms of the circuit. It can be realized with simple control.

In the above embodiment, the howling frequency is determined by the sound reproduced from the speaker, but the howling frequency may be automatically detected from the frequency characteristics of the acoustic signal output by the equalizer. . By doing so, howling can be automatically removed.

In the above embodiment, the case of removing howling has been described, but other abnormal sound components included in the sound output from the speaker may be removed.

Further, although the second-order IIR type filter is used in the above-mentioned embodiment, other digital filters such as FIR type filter may be used.
Further, the number of connecting stages of the filter and the interval at which the center frequency changes are not limited to those in the above-described embodiment.

[0038]

According to the present invention, the abnormal sound component can be removed by the processing using only the equalizer, and the operation of removing the abnormal sound component can be simplified.

In this case, the howling sound can be easily removed by performing the howling sound removing process.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a filter of an equalizing device according to an exemplary embodiment.

FIG. 3 is a plan view showing a display example when the equalizer of one embodiment is a parametric equalizer.

FIG. 4 is a plan view showing a display example when the equalizer of one embodiment is used as a notch filter.

FIG. 5 is a characteristic diagram when the equalizer of one embodiment is a parametric equalizer.

FIG. 6 is a characteristic diagram showing an amplitude adjustment state when the equalizer of one embodiment is a parametric equalizer.

FIG. 7 is a characteristic diagram when the equalizer of one embodiment is used as a notch filter.

FIG. 8 is a characteristic diagram showing an amplitude adjustment state when the equalizer of one embodiment is a notch filter.

FIG. 9 is a flowchart showing howling removal processing according to an embodiment.

FIG. 10 is an explanatory diagram showing a howling removal state according to an embodiment.

FIG. 11 is a configuration diagram showing a conventional acoustic processing configuration for howling removal.

[Explanation of symbols]

 1 Microphone 2 Mixing Console 3 Output Amplifier 4 Speaker 10 Equalizer 12 Digital Audio Data Processing Circuit 14 Central Control Unit (CPU)

Claims (3)

[Claims] 1. A sound processing method for outputting an input sound signal from a speaker via an equalizer, comprising the step of increasing the gain of a predetermined frequency of the equalizer.
An acoustic processing method in which the center frequency is moved to emphasize an abnormal sound component, and then the filter coefficient of the equalizer is changed to a coefficient showing a notch filter characteristic to remove the abnormal sound component. 2. The acoustic processing method according to claim 1, wherein the acoustic signal picked up by the microphone is supplied to the equalizer. 3. The acoustic processing method according to claim 2, wherein the abnormal sound component is a howling sound.