JP2004032362A - Gain limiting circuit - Google Patents

Abstract

When a signal is limited by a clipping circuit, a waveform is significantly distorted when a conventional gain limiting circuit is used. In particular, when audio data is handled, distortion of the signal is output as a higher harmonic wave, thereby deteriorating audibility. Let me do it.
A delay element, a level detector for detecting the amplitude of an output signal of the delay element, and an output signal of the delay element having an amplification degree corresponding to the output signal of the level detector are output. And an adder (subtractor) 2 for outputting the result of addition (subtraction) of the input signal and the output of the amplifier 6 to the delay element 3. The amplitude of the input signal for limiting the gain of the output signal is large. By reducing the gain as much as possible and amplifying the signal, the amplitude of the signal is suppressed and clipping is prevented.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gain limiting circuit for an audio signal by digital signal processing which is used in a digital audio device or the like and automatically suppresses an excessive output of an output signal.
[0002]
[Prior art]
FIG. 3 shows a conventional gain limiting circuit. The input signal from the input terminal 1 is filtered by the delay element 3 to extract a specific band signal, the obtained signal is amplified by the amplifier 7, and the clipping circuit 9 exceeds the maximum value allowed at the output terminal 8, The signal amplitude is limited so that a value less than the minimum value is not output.
[0003]
FIG. 4 is a diagram showing the relationship between the input signal amplitude and the output signal amplitude obtained in FIG. Although the input signal is amplified to a certain level, the amplitude does not increase further when the output signal reaches the maximum value or the minimum value allowed, so that a constant amplitude is obtained.
[0004]
[Problems to be solved by the invention]
However, when the above-described conventional gain limiting circuit is used, if the signal is limited by the clipping circuit 9, the waveform is significantly distorted. In particular, when audio data is handled, the distortion of the signal is output as harmonics, and the audibility is reduced. Will make it worse.
[0005]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a gain limiting circuit that suppresses signal amplitude and prevents clipping by lowering and amplifying the gain as the amplitude of the input signal increases, in order to solve the above problem. .
[0006]
[Means for Solving the Problems]
The present invention provides a delay element, a detector for detecting an amplitude of an output signal of the delay element, an amplifier for causing the output signal of the delay element to have an amplification degree corresponding to the output signal of the detector, and outputting the amplified signal. An adder / subtractor that outputs the result of addition (subtraction) of the input signal and the output of the amplifier to the delay element is provided to limit the gain of the output signal.
[0007]
According to the present invention, with the above-described configuration, an amplification effect can be obtained with a smooth gain limiting characteristic even for an excessive input of an input signal.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram showing a configuration of a gain limiting circuit according to one embodiment of the present invention. 1, the delay element 3 and the amplifier 7 are the same as those shown in FIG. Further, the adder 2, the level detector 4, the control circuit 5, and the amplifier 6 constitute a feedback circuit for limiting the gain.
[0009]
The operation of the present embodiment configured as described above will be described below.
[0010]
First, the signal input from the input terminal 1 is operated by the adder (subtractor) 2 with the feedback signal generated by the amplifier 6, and the operation result is input to the delay element 3. Here, the delay element 3 is a band limiting circuit such as a filter, the output of which is amplified by an amplifier 7 and output from an output terminal 8, while the level detector 4 detects the output amplitude of the delay element 3 and detects the output amplitude. Based on the result, the control circuit 5 determines the degree of amplification of the amplifier 6.
[0011]
Here, the gain limiting characteristic can be obtained even if the control circuit 5 outputs the signal only by multiplying the input by a constant. The amplifier 6 amplifies the output signal of the delay element 3, and the adder (subtractor) 2 again inputs the operation result with the signal input from the input terminal 1 to the delay element 3 to apply feedback.
[0012]
With this configuration, even when an excessive signal is input from the input terminal 1, the negative feedback increases as the amplitude level increases, so that the output amplitude at the delay element 3 is suppressed, and the strength of the negative feedback is controlled by the control circuit. If the setting is appropriately made in step 5, even if the signal is amplified by the amplifier 7, the output allowable range of the output terminal 8 can be prevented from being exceeded.
[0013]
FIG. 2 is a diagram showing the amplitude characteristics of the signals at the input terminal 1 and the output terminal 8 when the control circuit 5 has a threshold setting in the present embodiment. , And the solid line is the characteristic of the present embodiment. The operation of the present embodiment will be described below.
[0014]
First, the control circuit 5 compares the set threshold value with the amplitude value obtained by the level detection circuit 4, and when the amplitude value is smaller, that is, when the signal input from the input terminal 1 is smaller, the control circuit 5 The circuit 5 sets the amplification degree of the amplifier 6 to zero and does not generate a feedback signal.
[0015]
As a result, the signal is amplified by the amplifier 7 via the delay element 3 without reducing the amplitude of the signal by the adder / subtractor 2. When the amplitude value obtained by the level detector 4 is larger than the threshold value set by the control circuit 5, a feedback signal is generated by setting the amplification degree of the amplifier 6 by the control circuit 5, and a feedback signal is generated. ) Feedback is applied to the input to the arithmetic unit 2.
[0016]
In other words, when the control circuit 5 is provided with a threshold setting, it is possible to determine whether to perform gain limitation or not based on the signal amplitude from the input terminal 1. When the signal amplitude is small, sufficient amplification is performed. However, when it becomes large, the gain is limited and the output amplitude can be suppressed. Here, the control circuit 5 can be configured with an arithmetic unit that performs an operation on the output of the level detector 4, a table that outputs the corresponding coefficient, and the like.
[0017]
Also, in the level detector 4, a circuit that changes the output signal of the detector quickly when the amplitude value of the detected signal increases, and changes the output signal of the detector slowly when the amplitude value of the detected signal decreases, for example, detection. If a circuit is used, by changing the amplification degree of the amplifier 6 by the control circuit 5 in accordance with this change, even if an excessive signal is input to the input terminal 1, feedback is quickly performed and the gain can be controlled.
[0018]
On the other hand, when the signal amplitude at the input terminal 1 suddenly decreases, the amplitude can be smoothly changed by gradually reducing the feedback by gradually weakening the feedback.
[0019]
By using a low-pass filter as the delay element, clipping of the output signal can be prevented even for an excessive input of a low-frequency component of the input signal, and a smooth waveform can be output.
[0020]
【The invention's effect】
As described above, the present invention can be obtained at the output of the delay element by negatively feeding back the signal having the determined amplification degree by detecting the signal amplitude level of the output of the delay element to the input section of the delay element. By limiting and amplifying the amplitude, an amplification effect can be obtained with a smooth gain limiting characteristic within the amplitude range allowed at the output terminal. Further, since high-frequency distortion unlike a clipping circuit does not occur, it is particularly useful as a gain limiting circuit for audio signals.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a gain limiting circuit according to an embodiment of the present invention; FIG. 2 is an amplitude characteristic diagram of the gain limiting circuit of the present embodiment; FIG. FIG. 4 is an amplitude characteristic diagram of a conventional gain limiting circuit.
Reference Signs List 1 input terminal 2 adder (subtractor) 3 delay element 4 level detector 5 control circuit 6 amplifier 7 amplifier 8 output terminal

Claims (5)

A delay element, a detector for detecting an amplitude of an output signal of the delay element, an amplifier for outputting the output signal of the delay element with an amplification degree corresponding to the output signal of the detector, and an input signal; A gain limiting circuit, comprising: an adder / subtractor that outputs a result of addition / subtraction of an output of an amplifier to the delay element, and limits a gain of an output signal. 2. The gain limiting circuit according to claim 1, wherein the use of a low-pass filter as the delay element prevents clipping of the output signal even for an excessive input of a low-frequency component of the input signal and outputs a smooth waveform. . The detector outputs a signal that makes the amplification of the amplifier zero when the detected amplitude value is equal to or less than a set value, and outputs a signal that causes the amplifier to have an amplification corresponding to the detector output when the detected amplitude value is equal to or more than the set value. 2. The gain limiting circuit according to claim 1, wherein the gain characteristic of the output signal is changed according to the amplitude of the input signal according to the set value. In the detector, when the amplitude value of the detected signal is large, the output signal of the detector is changed quickly, and when the amplitude value of the detected signal is small, the output signal of the detector is changed slowly, so that an excessive input 2. The gain limiting circuit according to claim 1, wherein a smooth waveform can be output by quickly suppressing the gain of the output signal with respect to the signal and slowly changing the return of the gain of the output signal after the excessive input signal. A filter circuit, a detector for detecting an amplitude of an output signal of the filter circuit, an amplifier for outputting an output signal of the filter circuit with an amplification degree corresponding to the amplitude detected by the detector, and an input signal. A gain limiting circuit comprising an adder (subtractor) for outputting a result of addition (subtraction) of the output of the amplifier to the filter circuit.

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