JPH03216008A - Graphic equalizer - Google Patents

Abstract

PURPOSE:To reduce the residual noise without changing a boosting quantity by making the gain of a band pass filter >=1 to decrease an adder coefficient. CONSTITUTION:The adder coefficient is decreased by making the gain of a band pass filter >=1. For example, band dependent sound quality adjustment circuits T1-Tn have different center frequencies and made up respectively of plural band pass filters 11-1n whose gain is '2', resistors Rx1-Rxn and sound quality adjustment variable resistors RV1-RVn. In such a case, when the same boosting quantity of the gain as the case with employing band pass filters is obtained, the resistors Rx inserted between the outputs of the band pass filters 11-1n and an input of an operational amplifier 2 are selected larger. Thus, the coefficient R4/Rx is decreased and noise generated in the band pass filters is reduced without changing the boosting quantity and the residual noise is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a graphic equalizer that adjusts sound quality for each frequency band, and particularly relates to a graphic equalizer that can reduce residual noise.

[Conventional technology]

Conventionally, in order to adjust the sound quality of music played from audio equipment to the listener's preference, audio equipment has been equipped with a sound quality correction device called a tone control that can adjust the strength of the high or low range of the sound. A sound quality adjustment device called a graphic equalizer is sometimes provided, which can divide the audio frequency band into several bands and freely add strength or weakness to the sound of the divided frequency bands. Among these, the graphic equalizer can freely add strength or weakness to the sound for each divided audio frequency band, so it is possible to create a sound field that matches the listener's preferences.

FIG. 4 shows an example of the configuration of a conventional graphic equalizer. In this case, A1 and A2 are inverting amplifiers, and operational amplifier 1 and resistor R. ,R. , operational amplifier 2 and resistors R,,R. It is composed of. Then, between the output of the operational amplifier 1 and the input of the operational amplifier 2, the frequency band of the input acoustic signal is divided into n parts,
Band-specific sound quality adjustment circuits T, -T7 are provided for assigning strengths and weaknesses to each of the divided bands. Each of the band-specific sound quality adjustment circuits T1 to T, . is provided with a band-pass filter (band-pass filter, shown in the figure) having a different center frequency.
PF1 to BPFn) 21 to 2n, and resistors RX1 to
RXn, and sound quality adjustment volumes RVL to RVn. In addition, in this example, the sound quality adjustment volume R
The midpoint of VI to RVn is grounded, one terminal a is connected to the human power side of operational amplifier 1, the other terminal b is connected to the human power side of operational amplifier 2, and each sound quality adjustment volume RVI to R
When Vn is moved to the terminal b side, the level of that band is most emphasized (boosted).

[Problems to be Solved by the Invention] However, in the conventional graphic equalizer, when the level of the frequency of the divided band is boosted, the bandpass filters 21 to 2 of the band-specific sound quality adjustment circuits T1 to Tfl are boosted.
Since the noise Bn generated by n is added and output, the residual noise increases, which may cause problems in terms of sound quality.

This will be explained using FIG. 5, but to simplify the explanation, it is assumed that in the circuit of FIG. 5, only one tone quality adjustment circuit T is connected to the inverting amplifiers At and A2. Now, in the inverting amplifier Al, A2, the resistor R, one resistor R
2, and resistor R: l - resistor R4 (therefore, the gains of inverting amplifiers AI and A2 are both -1), and the volume of sound quality adjustment circuit T is boosted to the maximum (equivalently, resistor Rx is directly (connected to the input side of the operational amplifier 2), the transfer characteristic of the bandpass filter 20 is H (s), and the noise generated in the bandpass filter 20 is Bn, then the transmission of the graphic equalizer shown in FIG. The characteristics are as shown in the following equation.

As you can see from this second figure, the residual noise Bn is R4/R
The residual noise increases because it is multiplied by X and added and output.

It is an object of the present invention to solve the problems of the conventional graphic equalizer, and to reduce the noise generated in the bandpass filter and the residual noise in the graphic equalizer without changing the amount of boost. .

[Means to solve the problem]

The present invention achieves the above object by converting an input acoustic signal into
A graphic equalizer that adjusts sound quality using a plurality of active hand-pass filters having different center frequencies is characterized in that the gain of the hand-pass filters is increased above 1 to reduce the addition coefficient.

[Effect]

According to the graphic equalizer of the present invention, by increasing the gain of the bandpass filter, when obtaining the same amount of boost as when using a handpass filter with a gain of 1, the output of the bandpass filter and the operational amplifier The value of the resistor RXO inserted between the input and the input can be increased. As a result, the coefficient R. The value of /RX can be made small, and residual noise is reduced.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the structure of an embodiment of a graph ink equalizer according to the present invention, and the same members as in the conventional graphic equalizer are given the same reference numerals.

In the figure, Al and A2 are inverting amplifiers, each connected to an operational amplifier 1 and a resistor R. , R2, an operational amplifier 2, and resistors R3 and R4. Between the output of the operational amplifier 1 and the input of the operational amplifier 2, there is a band-specific sound quality adjustment circuit T, which divides the frequency band of the input acoustic signal into n parts and adds strength and weakness to each divided band. T.
is provided.

Each band-based sound quality adjustment circuit T1 to T7 includes a plurality of hand-pass filters (BPFI to BPFn in the figure) having different center frequencies and a gain of 2.
and resistance RX, %RX. , and sound quality adjustment volume R
VI to RVn are provided. In this embodiment as well, the midpoint of the sound quality adjustment volumes RVI to RVn is grounded, one terminal a is connected to the input side of the operational amplifier 1, and the other terminal b is connected to the input side of the operational amplifier 2. When the volumes RVI-RVn are moved to the terminal b side, the level of that band is most emphasized (boosted).

FIG. 2 shows an example of a specific circuit configuration of one hand-pass filter 0 of the graphic equalizer configured as described above. The bandpass filter 0 is composed of, for example, two operational amplifiers 3, 4, five resistors R, -R, and two capacitors C1, C2, and has a center frequency f. and sharpness Q are expressed by the following formula.

1 Here, c, = cz = C, Rs = R6, R = 1/
(2 rtf.c), assuming that the gain at the center frequency f0 is A0, R, = 2 lines Q * R SR 7 = R umbrella Q / A
o, Re = R/[2*Q (A+1/(2IQ)
)].

And the center frequency f of the bandpass filter. , sharpness Q
By setting the value of R and the gain 2, the resistor R
, , R 8 , and Rq can be determined.

Next, the transfer characteristics of the graphic equalizer of the embodiment configured as above will be explained using FIG. 2. Note that the circuit in Figure 2 includes an inverting amplifier A to simplify the explanation.
l. It is assumed that only one sound quality adjustment circuit T is connected to A2. Now, in the inverting amplifier ^1, A2,
Similar to the conventional example explained in FIG. 5, resistance RI=resistance Rt,
It is assumed that the resistor R3 is equal to the resistor R4, the gains of the inverting amplifiers ^1 and A2 are both -1, and the volume of the sound quality adjustment circuit T is boosted to the maximum. At this time, equivalently, there is a resistor Rx between the output of the bandpass filter 10 and the input of the operational amplifier 2.

Then, the transfer characteristic of the bandpass filter 10 is expressed as H(S)
and the noise generated in the bandpass filter 10 is Bn
Then, the transfer characteristic of the sound quality adjustment device shown in FIG. 2 can be expressed by the following equation.

Vtll RXHere, conventionally, the transfer characteristic at the center frequency f0 of the bandpass filter 10 was H(s)=1, so for example, (R a
/Rx)XH(s) was 3, the coefficient R4/RXO value was 3, and the residual noise was 3Bn. However, in the above embodiment, H(s)
= 2, so similarly (R4 / RX ) X H
In order to set the value of the term (S) to 3, the coefficient R4/RX
The O value may be 1.5. Then, the residual noise is 1.58n
Therefore, the noise level is theoretically improved by 6 dB compared to the conventional method. However, due to the increase in noise components due to the increase in the gain of the bandpass filter 10,
The actual noise level improvement is less than this.

FIG. 3 shows the noise distribution obtained using the graphic equalizer of FIG. 1 over the entire frequency band of the acoustic signal in comparison with the conventional graphic equalizer shown in FIG. In the figure, the solid line is the noise distribution by the conventional graphic equalizer, the dotted line is the noise distribution by the graphic equalizer of the embodiment shown in Figure 1, and what is shown on the right side of the figure is a comparison of the noise level of the entire graphic equalizer. This is shown below. As can be seen from this figure, the noise level of the graphic equalizer of the first embodiment shown in FIG. 1 is improved by about 2 dB compared to the conventional graphic equalizer shown in FIG. 4.

〔Effect of the invention〕

As described above, according to the present invention, residual noise can be reduced without changing the amount of boost in a graphic equalizer that divides frequencies to adjust sound quality.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the graphic equalizer of the present invention, FIG. 2 is a circuit diagram showing an example of the configuration of the bandpass filter of FIG. 1, and FIG. 3 is a noise noise caused by the graphic equalizer of the present invention. Figure 4 is a circuit diagram showing the configuration of a conventional graphic equalizer; Figure 5 is a diagram of one hand-pass filter of the graphic equalizer in Figure 4. FIG. 3 is an equivalent circuit diagram when boost t is increased to i. L 2, 3.4... operational amplifier, 10~in, 20~2n... hand pass filter,
At, A2...Inverting amplifier, RVI~RVn...Volume, T1~Tn...Tone quality adjustment circuit.

Claims (1)

[Claims] A graphic equalizer that adjusts the sound quality of an input acoustic signal using a plurality of active band-pass filters having different center frequencies, characterized in that the gain of the band-pass filters is increased above 1 to reduce the addition coefficient. .