JPS6221443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio input circuit for frequency modulation in television audio multiplexing, and more particularly to an audio amplitude limiting amplifier.

FIG. 1 is a diagram showing the configuration of a conventional audio amplitude limiting amplifier.
After that, it is sent to the amplitude limiting amplifier 2. This is because overmodulation and the like are strictly restricted in television audio multiplexing. Amplitude limit amplifier 2
has a characteristic that the amplification degree is saturated when the amplitude of the signal is above a predetermined value. After passing through the amplitude limiting amplifier 2, the audio signal is supplied to a modulator (not shown) via a clip circuit 3 and a low pass filter 4. In the amplitude limiting amplifier 2, the amplitude is detected by an amplitude detection circuit 5 in order to control the degree of amplification according to the amplitude of the signal, and the detected voltage includes an attack/recovery time setting circuit 6 in which attack time and recovery time can be set independently. The signal is then supplied to the amplitude limiting amplifier 2.

As shown in Figure 1, since the attack time and recovery time have an audible effect on the high-frequency components of the audio signal, the attack time is lengthened to a certain extent to suppress the amplitude of the high-frequency components, and the recovery time also has an effect on the audibility. The decision has been taken into consideration. During the attack time, a signal whose amplitude is not limited is output, and at this time it is clipped by the clipping circuit, but the distortion in the high frequency component is improved by the subsequent low-pass filter, but the distortion in the low frequency component is not improved. It was hot. Also,
In principle, the shorter the recovery time, the better; however, in reality, the output of the amplitude detection circuit contains a low-frequency component signal, so if the recovery time is shortened, the amplitude limit control is continuously applied. The disadvantage was that distortion in the low frequency components increased.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an audio amplitude limiting amplifier that can eliminate the conventional drawbacks and suppress distortion of low frequency components.

According to the present invention, it is possible to obtain an audio amplitude limiting amplifier in which attack time and recovery time can be set respectively for high-frequency and low-frequency components of an audio signal.

Next, the present invention will be described in detail with reference to the drawings showing one embodiment of the present invention. FIG. 2 is a diagram showing an embodiment of the present invention. Compared to FIG. 1, in order to separate the loop for controlling the amplification degree of the amplitude limiting amplifier 2 into high and low frequencies, a low-pass filter 7 and a high-pass The filter 8 includes an amplitude detection circuit 5a, an attack/recovery time setting circuit 6a, an amplitude detection circuit 5b, and an attack/recovery time setting circuit 6b following the filters 7 and 8, respectively. Furthermore, a high-pass filter 9 is inserted before the clip circuit 3. In Figure 2, the attack time for the low frequency component is, for example, 50 μsec.
The recovery time is set to 2.5 μsec, for example. On the other hand, the attack time for the high frequency component is set to, for example, 6.5 mS, and the recovery time is set to, for example, 700 mS. As described above, the attack time of the high-frequency components that affect the auditory sensation can be set long to reduce the effect, and the attack time of the low-frequency components that do not affect the auditory sensation can be set short. Furthermore, the recovery time for low-frequency components that affect the distortion rate of low-frequency audio can be set long to reduce the effect, and the recovery time for low-frequency components that do not affect the distortion rate of low-frequency audio can be set short. By doing so, it is possible to prevent an increase in low-frequency distortion as in the conventional case. The purpose of the high-pass filter 9 is to guide only the high frequency components of the signal whose amplitude is not limited during the attack time to the clip circuit 3.

As explained above, the present invention improves auditory sensation and reduces the distortion rate of low-frequency components of audio by configuring the amplitude limit detection section so that the attack time and recovery time can be arbitrarily set according to each frequency band. It has an improving effect.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional audio amplitude limiting amplifier.
FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, 1... pre-emphasis circuit, 2
...amplitude limiting amplifier, 3...clip circuit, 4,
7... Low pass filter, 5, 5a, 5b... Amplitude detection circuit, 6, 6a, 6b... Attack/recovery time setting circuit, 8, 9... High pass filter.

Claims (1)

[Claims] 1: an amplitude-limiting amplifier circuit whose amplification degree changes depending on a control voltage; a first low-pass filter that receives the output of the amplitude-limiting amplifier circuit; a first high-pass filter that receives the output of the amplitude-limiting amplifier circuit; first and second amplitude detection circuits detecting the outputs of the low-pass filter and the first high-pass filter, respectively, and receive the output voltages from the first and second amplitude detection circuits, respectively, and detect the rise and fall of the voltage signal. first and second attack/recovery time setting circuits capable of individually setting falling time constants; a second low-pass filter receiving the output of the amplitude limiting amplifier circuit; and a second low pass filter receiving the output of the amplitude limiting amplifier circuit. A series circuit including a second high-pass filter and a clip circuit is provided, and the rising time constant of the first attack/recovery time setting circuit is compared with the falling time constant of the second attack/recovery time setting circuit. The falling time constant of the first attack/recovery time setting circuit is set to be larger than the falling time constant of the second attack/recovery time setting circuit; An audio amplitude limiting amplifier characterized in that the output of the second attack/recovery time setting circuit is used as a control voltage of the amplitude limiting amplifier circuit.