JPH0227619Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a frequency characteristic compensation circuit, which is suitable for use, for example, in compensating for deterioration of frequency characteristics due to various losses in the recording and reproduction process.

BACKGROUND TECHNOLOGY AND PROBLEMS There is, for example, a graphical equalizer that independently adjusts the response in multiple frequency bands as a frequency characteristic compensation circuit of this kind.
Today, they are finding increasing utility in audio and studio equipment, for example. However, these conventional graphical equalizers independently adjust the response in the frequency band, and the usable range is adjustment (boost) between a flat value and a predetermined maximum enhancement value, or adjustment (boost) between a flat value and a predetermined maximum enhancement value. The gain in the frequency band obtained by these adjustments is made constant regardless of the magnitude of the input signal.

In such a graphical equalizer, for example, when the gain in a frequency band is increased by adjustment, when an input signal with a large signal level is given, this input signal is kept in a state with a good S/N ratio and the predetermined adjustment is made. Since the signal is amplified up to that point, the noise component contained in the signal is not noticeable. In other words, the noise component is masked by the input signal level, so it does not cause any audible problem.
When an input signal at a small signal level is given, a specific band of this input signal is enhanced to a predetermined adjustment position, so it seems that there are more noise components in that signal than in the specific band. In this case, the signal component remains the same, but the noise component is enhanced,
As a result, there was a drawback that the noise became noticeable.

In addition, when the gain in the frequency band is attenuated by adjustment, when an input signal with a large signal level is given, this input signal is attenuated to the predetermined adjustment position while maintaining a good S/N ratio. Noise components are not noticeable and the input signal does not become so small that it becomes inaudible, so the sound does not become unpleasant to hear, but when an input signal at a small signal level is given, this input signal is attenuated to a predetermined adjustment position. The drawback was that the sound became so low that it became inaudible, and that it was masked by the inherent noise components originally generated by the amplifier itself.

That is, conventional frequency characteristic compensation circuits such as graphical equalizers can exhibit their full performance for large signal level sounds, but have the disadvantage that they cannot fully demonstrate their performance for small signal level sounds.

Purpose of the invention In view of the above, the present invention provides a frequency characteristic compensation circuit that eliminates the drawbacks of the conventional circuit described above and can provide a sense of dynamism without losing dynamic balance depending on the input signal level. It is something.

Summary of the invention In this invention, the first
and a second adder, variable gain means to which the output signal of the first adder is supplied, and a control signal generator that detects the input signal, converts it into a DC signal, and supplies it as a control signal to the variable gain means. means for controlling the gain of the variable gain control signal to become smaller as the input signal becomes smaller by the control signal, and selectively controlling the output signal of the variable gain control signal to the first or second one. By supplying the signal to the adder and controlling the frequency characteristics, it is possible to make noise components less noticeable, especially when the input signal is at a low level, and it is possible to create a sense of dynamism without losing dynamic balance depending on the input signal level. It will be done.

Embodiments Hereinafter, embodiments of this invention will be described in detail based on FIGS. 1 to 8.

FIG. 1 shows the circuit configuration of the first embodiment of this invention. In the figure, 1 is an input terminal to which an audio signal is supplied, and the input signal from this input terminal 1 is sent to a first adder. The output signal is supplied to, for example, a high-gain phase-inverting operational amplifier 2 as a second adder having the same circuit configuration as this operational amplifier 2, for example, a high-gain phase-inverting operational amplifier 3. A desired output signal whose frequency characteristics have been appropriately compensated is taken out from an output terminal 4 on the output side of the operational amplifier 3.

Further, a voltage-controlled variable amplifier 5 is provided between the operational amplifiers 2 and 3, and the output side of the variable amplifier 5 has a plurality of passbands that collectively cover the frequency spectrum of the signals handled by this transmission system. Bandpass filters 6, 7, 8 are provided. Furthermore,
Potentiometers 12, 13, 14 are provided on the output sides of these bandpass filters 6, 7, 8 via resistors 9, 10, 11, respectively, and the central portions of these potentiometers 12-14 are grounded by fixed taps 12a, 13a, and 14a, respectively, and one end of each of these potentiometers 12 to 14 is connected in common and then connected to the other input side of the operational amplifier 2 to form a so-called feedback loop. However, their respective other ends are commonly connected and then connected to the other input side of the operational amplifier 3 to form a so-called feedforward loop. Therefore,
The sliding terminals 12 of these potentiometers 12 to 14 are connected to one end of each of the resistors 9, 10, 11.
When b, 13b, and 14b are located at their central portions, the feedback amount, or attenuated component, and the feedforward amount, or boost component, are equal, and the response in the corresponding frequency band is flat. On the other hand, these bandpass filters 12 to 1
Maximum attenuation or boost is achieved when the four sliding terminals 12b-14b are at the extremes. That is, the sliding terminals 12b to 14b of the bandpass filters 12 to 14 are connected to the fixed taps 12, respectively, in the drawing.
Feedback is applied when the terminals are located to the left of a, 13a, 14a, while the sliding terminals 12b, 1
4b are fixed taps 12a, 13a, 1, respectively in the drawing.
When located to the right of 4a, a feed forward is applied.

Further, in order to control the gain of the variable amplifier 5, the input signal from the input terminal 1 is supplied to the detection circuit 15, where double-wave detection in the positive direction is performed. In addition,
In this detection circuit 15, negative direction double wave detection is also possible by changing the direction of the diode. The signal detected here is transmitted to the peak detection circuit 1
6, and the peak value is extracted from the signal waveform subjected to double-wave detection. Peak detection circuit 16
The output signal from is supplied to the time constant circuit 17,
Here, based on the time constant, the peak detection circuit 16
The peak value from is held for a certain period of time. The output signal from the time constant circuit 17 is supplied to a limiter circuit 18, which has a predetermined threshold level V _TH as shown in FIG. By limiting the _voltage above a certain level, that is, above the threshold level V _TH , a control voltage proportional to the input signal level _is obtained. In the case of a signal, the limiter circuit 18 supplies the value at the threshold level _VTH to the variable amplifier 5 as a control voltage.

In other words, these detection circuits 15 to limiter circuits 1
8 constitutes a control system as a control signal generating means for controlling the gain of the variable amplifier 5, and in this control system, the input signal is set at the above threshold level V _TH
When the input signal voltage is within 0, the control voltage is 0 when the input signal voltage is 0, as shown in FIG. 3, but as the input signal voltage increases, the control voltage also increases accordingly. ing.

The gain of the variable amplifier 5 is normally designed to increase in proportion to the control voltage, as shown in FIG. 4, but by providing the control system with a limiter function as described above, As shown in Figure 5, the control voltage is at the threshold level.
When the input signal level is lower than V _TH , that is, when the input signal level is low, the gain is attenuated in the negative direction, thereby attenuating the signal component passing from the operational amplifier 2 to the variable amplifier 5 . Therefore, a preset constant feedback component or feedforward component provided by the potentiometers 12 to 14, to which this attenuated signal component is supplied through each bandpass filter 6 to 8, respectively, is transmitted to the operational amplifier, respectively. 2 and 3 will be supplied to the other input side.

Also, the control voltage supplied to the variable amplifier 5 is
As shown in the figure, when the input signal level is higher than the threshold level V _TH , that is, when the input signal level is high, the amount of attenuation in the variable amplifier 5 becomes 0, so that the attenuation amount from the operational amplifier 2 passes through the variable amplifier 5 to the bandpass filter 6.
The signal components in the system leading to 8 are transmitted through the variable amplifier 5
potentiometer 1 without any damping at
2 to 14, a predetermined constant feedback or feedback component provided by these potentiometers 12 to 14 is applied to the other input of operational amplifiers 2 and 3, respectively. That will happen.

Therefore, substantially the potentiometers 12 to 14
When the control voltage supplied to the variable amplifier 5 is lower than its threshold level V _TH when the adjustment gain of the variable amplifier 5 is set to the maximum point,
At the output terminal 4, a signal having a frequency characteristic as shown in FIG. 6 in the case of boost and as shown in FIG. . On the other hand, when the control voltage supplied to the variable amplifier 5 is higher than the threshold level _VTH , the amount of attenuation in the variable amplifier 5 becomes 0, as can be seen from FIG.
~14 corresponding to the position where the adjustment gain is maximum
A signal having frequency characteristics as indicated by the symbols shown in the figure (in the case of boost) or FIG. 7 (in the case of attenuation) is extracted. In other words, the maximum value of the adjustment gain of the potentiometers 12 to 14 remains constant when the input signal is greater than the threshold level V _TH , but when the input signal is less than the threshold level V _TH The maximum value is decreased depending on the level of the input signal.

In this way, in this embodiment, when the input signal is below a predetermined level, the gain or attenuation of the variable amplifier 5 is substantially reduced according to the level of the input signal, so that the noise component contained in the input signal is reduced. Nothing stands out.

In the circuit shown in FIG. 1, the variable amplifiers 5 may be provided on the other input sides of the operational amplifiers 2 and 3, respectively, and these variable amplifiers 5 may be controlled by the control voltage from the limiter circuit 18.

Figure 8 shows a second embodiment of this invention.
In this figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, the frequency band of the transmission system is divided into a plurality of bands, and each band is changed individually depending on the level of the input signal. Therefore, voltage-controlled variable amplifiers 5a, 5b, and 5c are provided between the operational amplifiers 2 and 3 for each band, and their output sides are connected to the respective sliding terminals of the potentiometers 12 to 14 via band pass filters 6 to 8 as described above. 12b-14
b, respectively. Each end of these potentiometers 12 to 14 is connected to an operational amplifier 2.
The connection to the other input side of 3 and 3 is the same as described above. Further, a plurality of detection circuits 15a to 15c and peak detection circuits 16a to 1 are provided according to each divided band.
6c, time constant circuits 17a to 17c, limiter circuits 18a to 18c are provided, and detection circuits 15a to 15c are provided.
Bandpass filters 19a to 19c are provided on the input side of the filter 15c according to each divided frequency band. still,
These bandpass filters 19a to 19c have the same band characteristics as the bandpass filters 6, 7, and 8, respectively. And limiter circuit 1
The output signals of 8a to 18c are supplied as control signals to variable amplifiers 5a to 5c, respectively.

Although the operation of the circuit shown in FIG. 8 differs depending on the frequency band, its basic operation is the same as that of the circuit shown in FIG. 1, so its explanation will be omitted here.

Therefore, this embodiment has the advantage that noise components can be reduced for each band by individually changing the gain of the transmission system for each divided frequency band depending on the level of the input signal.

In addition, in this FIG. 8, the variable amplifiers 5a to 5
Similar effects can be obtained even if the arrangement of bandpass filters 6 to 8 is exchanged with each other.

Application Example In the above embodiment, the invention is applied to a graphic equalizer, but the invention is not limited to this, and can be applied to other frequency characteristic compensation circuits that require such a function. Similarly applicable.

Effects of the invention As described above, according to this invention, when the input signal level is low, the variable range of frequency characteristics is reduced to suppress excessive enhancement of noise components in a specific band, that is, the band in which the frequency characteristics are being adjusted. Therefore, when the specific band is a band in which there are more noise components than signal components, unnecessary enhancement of noise can be suppressed. Furthermore, by suppressing excessive enhancement of a specific band, it is possible to prevent signal components from falling below the inherent noise level. In this way, it is possible to give the sound a jumping feeling without losing the dynamic balance according to the input signal level.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing one embodiment of this invention, Figs. 2 to 7 are diagrams for explaining the operation of Fig. 1, and Fig. 8 is a system diagram showing another embodiment of this invention. It is a diagram. 2 and 3 are operational amplifiers, 5 is a voltage controlled variable amplifier, 6 to 8 are band pass filters, 12 to 14 are potentiometers, 15 is a detection circuit, 16 is a peak detection circuit, 17 is a time constant circuit, and 18 is a limiter. It is a circuit.

Claims (1)

[Claims for Utility Model Registration] First and second adders arranged in series in a transmission system; variable gain means to which the output signal of the first adder is supplied; and a means for detecting an input signal. control signal generating means which converts the input signal into a DC signal and supplies it to the variable gain means as a control signal, and controls the gain of the variable gain means to become smaller as the input signal becomes smaller by the control signal, A frequency characteristic compensation circuit characterized in that the output signal of the variable gain means is selectively supplied to the first or second adder via a bandpass filter to control the frequency characteristic.