JPH0113455Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an automatic volume adjustment device designed to prevent malfunctions when there is no signal or in a weak electric field.

In audio products such as car radios, the difference component between the audio signal from the speaker and the ambient noise signal from the microphone is detected, and the gain of the volume adjuster is controlled using a control signal according to the magnitude of this difference component. An automatic volume adjustment device configured as follows is used.

FIG. 1 is a block diagram showing a conventional automatic volume adjustment device, in which 1 is a signal source such as a tuner or deck, 2 is a preamplifier, 3 is a volume adjuster, 4 is a power amplifier, 5 is a speaker, 6 is a microphone,
7 is a microphone amplifier, 8 and 9 are level adjusters, 1
0 and 11 are rectifier circuits, 12 is a subtraction circuit, 13 is a reference signal generator, 14 is a comparison circuit, 15 is a gate circuit, and 16 is an integration circuit.

With the above configuration, the audio signal from the speaker 5 and the ambient noise signal from the microphone 6 are converted into DC voltages by the rectifier circuits 10 and 11, respectively, and both are added to the subtraction circuit 12, so that the difference between the two is A signal voltage based on the true ambient noise amount proportional to is detected. This noise signal voltage is applied to the gate circuit 15.
The signal is sent to the integrating circuit 16 via the 16-bit integrator circuit 16, where it is averaged and made into a control voltage, which is applied to the volume adjuster 3, which operates to vary the gain and adjust the volume. That is, the volume of the receiver is automatically adjusted according to the amount of ambient noise.

By the way, with only the above configuration, the signal from the signal source 1 may become silent when the tape is located between tracks, for example when using a tape deck, resulting in hysteresis noise, or when receiving a radio wave, the signal may become hysteresis noise. If the receiver is located in a valley, the electric field will be weak, so the receiver will generate noise during this time. At this time, the automatic volume control device malfunctions, regarding the noise as an audio signal, and works to further increase the noise and output it. Therefore, unnatural volume adjustment is performed, which is very unpleasant to the hearing sense.

Comparison circuit 1 is used to prevent such malfunctions.
In this comparing circuit 14, the audio signal is compared with the reference signal from the reference signal generator 13, and unless certain conditions are satisfied, the gate circuit 15 is turned off and the volume controller 3 is turned off. is configured to stop the operation. Here, the voltage value of the above reference signal needs to be set at the midpoint between the minimum level of the audio signal and the noise generation level when there is no signal; if this reference signal voltage drops too much, noise may cause errors. If it is too high, it will not work when the signal is small.

However, in the prior art, since the reference signal voltage is fixed at a constant value, there has been a problem that stable malfunction prevention cannot be performed when the level fluctuates.

The present invention has been developed in response to the above problems, and is an automatic volume control system that eliminates the drawbacks of the conventional automatic volume control circuit by configuring the reference signal applied to the comparator circuit to vary in proportion to the control signal from the integrating circuit. The object is to provide an adjustment device.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, the same parts as in FIG.

As described above, the reference signal from the reference signal generator 13 applied to the comparator circuit 14 is
It changes in proportion to the control voltage output from 6. Therefore, when hysteresis noise occurs when there is no signal when the tape is located between tracks, or when the reception state becomes a weak electric field, the difference component from the subtraction circuit 12 increases and the control voltage from the integration circuit 16 increases. However, since the reference signal voltage applied to the comparator circuit 14 also increases proportionally,
will now work properly. That is, even if the control voltage from the integrating circuit 16 increases due to the above-mentioned causes, the reference signal voltage also increases by that amount, so the comparison circuit 14 works to turn off the gate circuit 15, so the control voltage is adjusted to adjust the volume. is not supplied to vessel 3. Therefore, since the gain of the volume adjuster 3 does not increase, an increase in noise output is prevented.

As is clear from the above description, according to the present invention, the reference signal applied to the comparator circuit is configured to be varied in proportion to the control signal from the integrating circuit, so that natural volume adjustment can be performed. This allows for stable malfunction prevention. Therefore, it is possible to avoid unnecessary noise from being increased and causing discomfort to the listener.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are block diagrams showing a conventional device and an embodiment of the present invention. 12... Subtraction circuit, 13... Reference signal generator,
14... Comparison circuit, 15... Gate circuit, 16...
...integrator circuit.

Claims (1)

[Scope of utility model registration request] The difference component between the audio signal and the ambient noise signal is detected by a subtraction circuit, the difference component is added to an integrating circuit, and the volume adjuster is controlled by a control signal from this integrating circuit that corresponds to the magnitude of the ambient noise signal. The automatic volume adjustment device configured as above includes a comparison circuit for comparing the audio signal and a reference signal, and a gate circuit controlled by the comparison circuit and controlling the output of the subtraction circuit, and An automatic volume adjustment device characterized in that it is configured to vary a reference signal in proportion to a control signal from an integrating circuit.