JPH05191885A - Acoustic signal equalizer circuit - Google Patents

Abstract

PURPOSE:To reproduce sound quality rich in auditory sensation by adding a high frequency component in an audible band at the time of reproducing an acoustic signal restricted in the band. CONSTITUTION:Respective high frequency component signals EH1 to EH4 to be outputted from a component wave device 2 are added to envelope detectors 11-1 to 11-4 and square circuits 8-1 to 8-4. Higher harmonic component signals from the square circuits 8-1 to 8-4 are inputted to gain control circuits 10-1 to 10-4 via BPFs 9-1 to 9-4. Respective amplitude modulation signals which was modulated in amplitude by amplitude detection signals from the envelope detectors 11-1 to 11-4 and controlled in gain via attenuators 14-1 to 14-4 are fed to an addition circuits 11. The addition circuit 11 synthsizes the respective amplitude modulation signals with a low frequency component signal from the component wave device 2 and feds the synthesized signal to a switch 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic signal equalizer circuit for reproducing a sound rich in hearing when reproducing a band-limited audio signal.

[0002]

2. Description of the Related Art There is a suitable band for transmission and recording of acoustic signals, for example, 0 to 15 kHz, C for FM broadcasting.
In D, 0 to 20 kHz is a suitable transmission band. When the upper limit frequency of the transmission band and f _C, which can be seen as a kind of low-pass filter (LPF) to cut-off frequency f _C, f _C such that the frequency of the sound source is shown in FIG. 2 (a) In the following cases, there is no problem because the data is recorded or transmitted as it is even through the low pass filter (LPF).

However, as shown in FIG. 2B, the sound source f
_When there is a component of _C or more, the component of f _C or more is removed by the low-pass filter (LPF) and is transmitted or recorded to be as shown in FIG. 2C, so that the component of f _C or more is reproduced. Instead, a sound different from the original sound is played.

When the sound collecting technology is improved and the performance of the reproducing apparatus is improved as in recent years, the component of 15 kHz or more in FM, C
If the component of 20 kHz or more in D is removed, the sound quality may be deteriorated. Generally, audible sound is 20Hz-20
It is said to be kHz, but the sensitivity does not become zero at 20 kHz.

[0005]

In the past, the aim was to reproduce the acoustic signal under the band limitation of the transmission system described above. However, assuming that the original sound source has a frequency distribution of f _A as shown in FIG. 2A, the acoustic signal is cut at f _C because the transmission system and the recording system have a limited transmission band as described above. It will be passed through an off-frequency low-pass filter, and f _A
The signal with> f _C is deleted. As a result, even if the reproduction system faithfully reproduces, the component of f _A > f _C cannot be reproduced,
This is a problem from the perspective of faithful reproduction.

That is, since the band of f _A > f _C that is deleted contains a frequency component that generates rich high frequency sound, this component is used in a transmission system equivalent to the LPF as in the conventional case. If it is cut, the original sound cannot be reproduced faithfully and the sound quality deteriorates.

An object of the present invention is to provide a mode function capable of adding a high frequency component in the audible range deleted in the transmission system when reproducing a band-limited acoustic signal, and to make the mode function act as necessary to enhance the function. The purpose is to propose an audio signal equalizer circuit that enables to obtain various reproduced sounds.

[0008]

In order to achieve the above object, an acoustic signal equalizer circuit according to a first invention of the present application provides an acoustic signal including a low frequency component signal having a predetermined cutoff frequency or lower and a cutoff frequency higher than the cutoff frequency. A plurality of high frequency component signals divided into a plurality of different frequency bands, a frequency component separating means for separating the high frequency component signals, an amplitude detecting means for amplitude detecting each high frequency component signal to obtain a detection signal, and each high frequency component signal A harmonic component extracting means for extracting a harmonic component signal of a predetermined multiple from each of them, and an amplitude modulating means for amplitude-modulating each of the harmonic component signals by the detection signal to obtain each gain-controlled amplitude modulated signal; Signal synthesizing means for synthesizing each amplitude modulated signal and the low frequency component signal of the acoustic signal to obtain a synthesized signal.

In the acoustic signal equalizer circuit according to the second aspect of the present invention, the acoustic signal is divided into a plurality of low frequency component signals having a predetermined cutoff frequency or less and a plurality of different frequency bands having the cutoff frequency or more. High-frequency component signal of
A frequency component separating means for separating the high frequency component signal, an amplitude detecting means for amplitude detecting the high frequency component signal to obtain a detection signal, and a zero cross detecting means for detecting a zero cross point of the high frequency component signal and outputting a zero cross signal. , An amplitude modulation means for amplitude-modulating each of the zero-cross signals by the detection signal to obtain each amplitude-controlled amplitude-controlled signal, and a difference for extracting each difference component signal between each of the amplitude modulation signals and each of the high-frequency component signals. An acoustic signal equalizer circuit comprising: a component signal output means; and a signal synthesizing means for synthesizing each of the difference component signals and a low frequency component signal of the acoustic signal to obtain a synthesized signal.

Further, in the acoustic signal equalizer circuit of the third invention of the present application, the acoustic signal is divided into a low frequency component signal having a predetermined cutoff frequency or less and a plurality of different frequency bands above the cutoff frequency. A high-frequency component signal, a frequency component separation means for separating the high-frequency component signal, an amplitude detection means for amplitude-detecting each high-frequency component signal to obtain a detection signal, and a zero-cross point of each frequency component signal to output each zero-cross signal Zero-cross detection means, an amplitude modulation means for amplitude-modulating each of the zero-cross signals by the detection signal to obtain a gain-controlled amplitude-modulated signal, and each sum component of each of the amplitude-modulated signals and each of the frequency-component signals A sum component signal output means for extracting a signal, and a signal synthesizing means for synthesizing each sum component signal and the low frequency component signal of the acoustic signal to obtain a synthesized signal. And wherein the Rukoto.

The acoustic signal equalizer circuit of the fourth invention of the present application selects and outputs either the synthesized signal or the acoustic signal in the circuit of the first, second or third invention. It is characterized by having a selection output means.

[0012]

In the circuit of the first invention, the acoustic signal is separated into the low frequency component signal and the high frequency component signal divided into a plurality of different frequency bands. Each high-frequency component signal is amplitude-detected to obtain a detection signal, and each harmonic component signal of a predetermined multiple is extracted. Each harmonic component signal is amplitude-modulated by the detected signal, and each gain-controlled amplitude-modulated signal obtained by amplitude-modulation is combined with the low-frequency component signal.

In the circuit of the second invention, the zero-cross point of each high-frequency component signal is detected, and the obtained zero-cross signal is amplitude-modulated by the detection signal. Then, each difference component signal between each amplitude modulation signal and each high frequency component signal and the low frequency component signal are combined.

Further, in the circuit of the third invention, the sum component signal of each amplitude modulation signal obtained by amplitude-modulating the zero cross signal and each high frequency component signal and the low frequency component signal are combined.

According to the circuit of the fourth aspect of the present invention, in each of the circuits, the composite signal and the acoustic signal can be arbitrarily selected and output.

[0016]

Embodiments of the present invention shown in the drawings will be described below. FIG. 1 shows an embodiment of an acoustic signal equalizer circuit according to the first invention. In the figure, reference numeral 1 is a band-limited acoustic signal, and 2 is a demultiplexer, which corresponds to the frequency component separating means. The duplexer 2 has, for example, a cutoff frequency f _L of 1
4 low-pass filters and a 4-channel narrow-band band-pass filter of f _H1 , f _H2 , f _H3 , and f _H4 whose center frequency is f _L or more, and 3 is an output terminal of the low frequency component signal E _L. 4 to 7 are high frequency component signals E _{H1 to} E _H4
Output terminal of. 8-1 to 8-4 are squaring circuits and 9-
Reference numerals _{1 to} 9-4 are bandpass filters having a center frequency of 2f _H1 to 2f _H4 and constitute the harmonic component extracting means.

Gain control circuits (or amplitude modulation circuits) 10-1 to 10-4 constitute the amplitude modulation means. 11
-1 to 11-4 are envelope detectors, which constitute the amplitude detector. Reference numeral 12 is an adder circuit, which corresponds to the signal synthesizing means. Reference numeral 13 is an output signal, and 14-1 to 14-4 are attenuators. A switch 15 constitutes the selection output means.

The acoustic signal 1 is separated by the demultiplexer 2 into a low frequency component signal E _L having a cutoff frequency f _L or less and high frequency component signals E _{H1 to} E _{H4 in} different frequency bands of channels.

Each high-frequency component signal E _{H1 to} E _H4 is a squaring circuit 8
-1 to 8-4 and envelope detector 11-1 to 11-
4 and the output of each squaring circuit is subjected to bandpass filters 9-1 to 9-4 to extract harmonic component signals centered on 2f _{H1 to} 2f _{H4, respectively} .

[0020] Here, for example, if f _H1 center of the high frequency component signal E _H1 is E _H1 = e ₁ cosω _H1 and t (1), the square of the output E _H1 ² is ^{_{E H1 2 = (e 1 2}} /2 ^{_{) + (e 1 2/2}} ) cos2ω H1 t (2)

The component of the second term of the equation (2) is extracted via the bandpass filter. 3A shows the output characteristics of the demultiplexer 2, and FIG. 3B shows the bandpass filters 9-1 to 9-1.
9-4 shows the respective output characteristics of 9-4, where the 2f _H1 component is a ₁ , the 2f _H2 component is a ₂ , the 2f _H3 component is a ₃ , and the 2f _H4 component is a ₃ 2f _H4.
3 is added to the component below f _L as a ₄
As shown in (c), the component lost by the f _L cutoff filter can be restored.

The envelope detectors 11-1 to 11-4 detect the amplitudes of the high frequency component signals E _{H1 to} E _H4 , and send the detected signals to the gain control circuits 10-1 to 10-4, respectively. Each gain control circuit amplitude-modulates each harmonic component signal by each detection signal and outputs an amplitude-modulated signal whose gain is controlled so as to be proportional to the amplitudes a _{1 to} a ₄ of E _{H1 to} E _H4 , and outputs the attenuator. 14
The addition circuit 12 synthesizes the low frequency component signal E _L via -1 to 14-4.

Originally, it is better that the harmonic distortion is small.
As shown in the explanatory diagram of the auditory sensitivity of the auditory sense, the auditory sense has the frequency f _0.
It is known that at (1.5 to 2.5 kHz) or less, there is sensitivity to the phase of the sound, but for signals above f ₀ shown by the solid line in FIG. 4, the phase is insensitive and only the amplitude is felt. ing.

Therefore, if f _C > f _{0 in} FIG. 3, the components above f _C are not perceived as distortion, and the original signal source, that is,
It is as shown in FIG. 3 that the amplitude becomes closer to the signal before being cut off at f _C.

In the embodiment of FIG. 1, the attenuator 14
It is of course possible to set the coefficients of -1 to 14-4 to zero and the harmonic components to zero. Furthermore, each high frequency component signal E _H1 ~
It is also possible to add the third harmonic component obtained by multiplying E _H4 and the output component of each squaring circuit. Further, a switch 15 may be provided so that the output signal 13 (combined signal) from the adder circuit 11 and the acoustic signal can be selected.

FIG. 5 shows an embodiment of an acoustic signal equalizer circuit according to the second invention. The same reference numerals as those in FIG. 1 represent the same or similar circuits, and 16-1 to 16-4 are zero-cross generators. It constitutes a detection means. 17-1 to
A differential amplifier 17-4 constitutes the difference component signal output means.

First, the high frequency component signal E _H1 from the demultiplexer 2
(FIG. 6 (a)) is added to the zero-cross generator 16-1 and converted into a zero-cross signal (FIG. 6 (b)) having a clear square wave of rising and falling at 0 level.

An amplitude detector (envelope detector) 1
Reference numeral 1-1 shows the waveform shown in FIG. 6C in which the amplitude shown by the broken line in FIG. 6A is detected and the amplitude modulator 10-1 amplitude-modulates the zero-cross signal by the detected signal to perform gain control. To obtain an amplitude modulation signal of. The amplitude modulation signal and the high frequency component signal E _H1 are added to the differential amplifier 17-1,
The difference component signal of both signals shown in (d) is obtained. The amplitude modulation signal (FIG. 6C) is a high frequency component signal E _H1 (FIG. 6C).
Since the amplitude is the same as that in (a)), the fundamental wave component is canceled out in the difference component signal, and the harmonic component is the main component. This difference component signal is passed through the attenuator 14-1 to adjust the above harmonic component and input to the adder circuit 11.

Another high frequency component signal E _H2 from the demultiplexer 2
Similar processing is performed on E _H4 , and the addition circuit 11 combines the respective difference component signals and the low frequency component signal E _L and outputs a combined signal (FIG. 6E) 13 to the switch 15. ..

FIG. 7 shows an embodiment of an acoustic signal equalizer circuit according to the third invention, in which the same reference numerals as those in FIG. 5 represent the same or similar circuits, and 18-1 to 18-4 are adders, which are the sum components. It constitutes a signal output means. 19-1a, 19-1
b, 19-2a, 19-2b, 19-3a, 19-3
b, 19-4a, 19-4b are coefficients k ₁ were respectively _{linked, (1-k 1),} k 2, (1-k 2), k 3, (1-
k ₃ ), k ₄ and (1-k ₄ ) are a pair of attenuators, respectively.

The high-frequency component signal E _H1 is applied to the zero-cross generator 16-1, and the zero-cross signal shown in FIG. 8B is generated assuming that E _H1 has the waveform shown in FIG. 8A. This zero-cross signal is amplitude-modulated by the amplitude detection signal in the amplitude modulator (or gain control circuit) 10-1,
An amplitude modulation signal whose gain is controlled so that its amplitude is equal to E _H1 is output. The amplitude modulation signal and the high frequency component signal E _H1 are multiplied by k ₁ and (1-k ₁ ) by passing through attenuators 19-1a and 19-1b, respectively, and added by an adder 18-1 to obtain the signal shown in FIG. The sum component signal of the waveform of c) is sent to the adder circuit 11.

Similar processing is performed on the high frequency component signals E _H2 , E _H3 and E _H4 , but the coefficient of each attenuator is k ₁
Set <k ₂ <k ₃ < ₄ . The adder circuit 11 synthesizes each sum component signal and the low frequency component signal E _L , and outputs the synthesized signal 13 to the switch 15.

[0033]

As described above, according to the acoustic signal equalizer circuit of the present invention, a high-frequency component signal outside the band is added at the time of reproducing the band-limited acoustic signal to reproduce a sound quality rich in the sense of hearing. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a first invention of the present application.

FIG. 2 is a characteristic diagram showing a relationship between a frequency f _{A of a} sound signal and a transmission band.

FIG. 3 is a frequency characteristic diagram for explaining the operation of the embodiment of FIG.

FIG. 4 is an explanatory diagram of auditory frequency characteristics.

FIG. 5 is a block diagram showing an embodiment of the second invention of the present application.

6 is a waveform diagram for explaining the operation of the embodiment of FIG.

FIG. 7 is a block diagram showing an embodiment of the third invention of the present application.

8 is a waveform diagram for explaining the operation of the embodiment of FIG.

[Explanation of symbols]

 1 Acoustic Signal 2 Demultiplexer 8-1 to 8-4 Square Circuit 10-1 to 10-4 Gain Control (Amplitude Modulation) Circuit 11-1 to 11-4 Envelope (Amplitude) Detection Circuit 12 Adder Circuit 15 Switch 16 -1 to 16-4 Differential amplifier 18-1 to 18-4 Adder

Claims (4)

[Claims] 1. A frequency component separating means for separating an acoustic signal into a low frequency component signal below a predetermined cutoff frequency and a plurality of high frequency component signals divided into a plurality of different frequency bands above the cutoff frequency. An amplitude detecting means for amplitude-detecting each high-frequency component signal to obtain a detection signal, a harmonic component extracting means for extracting a harmonic component signal of a predetermined multiple from each high-frequency component signal, and each harmonic component Amplitude modulating means for amplitude-modulating a signal by the detection signal to obtain each amplitude-controlled signal whose gain is controlled, and signal synthesis for obtaining a synthesized signal by synthesizing each of the amplitude-modulated signals and the low-frequency component signal of the acoustic signal An acoustic signal equalizer circuit comprising: 2. A frequency component separating means for separating an acoustic signal into a low frequency component signal below a predetermined cutoff frequency and a plurality of high frequency component signals divided into a plurality of different frequency bands above the cutoff frequency. An amplitude detection means for amplitude-detecting each high-frequency component signal to obtain a detection signal, a zero-cross detection means for detecting a zero-cross point of each high-frequency component signal and outputting each zero-cross signal, and each of the zero-cross signals Amplitude modulation means for obtaining each amplitude modulation signal amplitude-modulated by the detection signal and gain-controlled, difference component signal output means for extracting each difference component signal between each of the amplitude modulation signals and each of the high frequency component signals, and A signal synthesizing means for synthesizing each difference component signal and a low-frequency component signal of the acoustic signal to obtain a synthesized signal. Road. 3. A frequency component separating means for separating an acoustic signal into a low frequency component signal below a predetermined cutoff frequency and a plurality of high frequency component signals divided into a plurality of different frequency bands above the cutoff frequency. An amplitude detection means for amplitude-detecting each high-frequency component signal to obtain a detection signal, a zero-cross detection means for detecting a zero-cross point of each frequency component signal and outputting each zero-cross signal, and each of the zero-cross signals Amplitude modulation means for obtaining respective amplitude modulation signals amplitude-modulated by the detection signal and gain-controlled, sum component signal output means for extracting each sum component signal of each of the amplitude modulation signals and each of the frequency component signals, An acoustic signal equalizer circuit comprising: a signal synthesizing unit that synthesizes each sum component signal and a low-frequency component signal of the acoustic signal to obtain a synthesized signal. 4. The acoustic signal equalizer circuit according to claim 1, further comprising a selection output unit that selects and outputs one of the synthesized signal and the acoustic signal.