JPH0113454Y2 - - 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 the gate circuit 1
5 to the integrating circuit 16 and averaged.
The control voltage is applied to the volume adjuster 3 and 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 radio waves, the signal from the signal source 1 may become silent due to hysteresis noise. If the receiver is located at a location where the receiver is located, the electric field will be weak and 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 of the Here, the voltage value of the 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 is too low, errors are likely to occur due to noise. , and if it is too high, it will not work when the signal is small.

However, in the past, since the reference signal voltage was fixed at a constant value, there was a problem that stable malfunction prevention could not be performed when the level fluctuated.

The present invention was made in response to the above problem, and the audio signal is branched to the first and second bandpass filters and applied to the comparison circuit, and the output difference between the first and second bandpass filters is calculated. It is an object of the present invention to provide an automatic gain adjustment device configured to control the operation of a gate circuit by a comparison circuit accordingly. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an automatic gain adjustment device according to an embodiment of the present invention. The same parts as in FIG. 10A and 10B are rectifier circuits connected in series to the first and second bandpass filters 17A and 17B, respectively. The audio signals that have passed through the first and second bandpass filters 17A and 17B are converted into a DC voltage by the rectifier circuits 10A and 10B, and then applied to the comparison circuit 14.

In the above, when the output difference between the first and second bandpass filters 17A and 17B exceeds a preset value, the comparison circuit 14
5 is turned on, so the subtraction circuit 12
The difference component from is sent to the integrating circuit 16.

Therefore, a control voltage corresponding to the magnitude of the ambient noise signal is applied from the integrating circuit 16 to the volume adjuster 3, so that its gain is adjusted.

On the other hand, when the output difference between the first and second bandpass filters 17A and 17B becomes equal to or less than a preset value, the comparison circuit 14 controls the gate circuit 15 to turn off, so that the difference component from the subtraction circuit 12 is is not sent to the integrating circuit 16. Therefore, the operation of the volume adjuster 3 is stopped.

That is, as shown in FIG.
If the passbands of the bandpass filters 17A and 17B are set to two parts of the audible band A, such as a band with a high signal level, such as a middle band B, and a band with a small signal level, such as a high band C, a normal audio signal is output. In this case, the level of the high frequency component is often lower than the level of the middle frequency component, so
There is a large difference between the outputs (rectified outputs) of 7A and 17B. Therefore, by setting the output difference using a certain constant value as a reference, the comparison circuit 14 can operate to turn on or off the gate circuit 15 depending on whether the reference setting value is higher or lower.

As a result, when there is no signal when the tape is located between tracks, hysteresis noise occurs, 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. In this case, the frequency components output from the first and second bandpass filters 17A and 17B have a wide band uniformly distributed from the middle range to the high range as shown by D in FIG. The difference becomes extremely small. Therefore, in this case, the comparator circuit 14 operates to turn off the gate circuit 15.

This makes it possible to adjust the volume without being affected by the magnitude of the absolute value level of the noise.

As is clear from the above description, according to the present invention, the audio signal is branched to the first and second bandpass filters and added to the comparator circuit, and the signal is divided into two bandpass filters. Since the comparator circuit is configured to control the operation of the gate circuit, the volume can be adjusted naturally, and malfunctions can be stably prevented.

Therefore, it is possible to avoid unnecessary noise from being increased and causing discomfort to the listener.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing conventional and embodiments of the present invention, and FIGS. 3 and 4 are characteristic diagrams for explaining the present invention. 12... Subtraction circuit, 13... Reference signal generator,
14... Comparison circuit, 15... Gate circuit, 16...
...Integrator circuit, 17A, 17B...Band pass filter.

Claims (1)

[Claims for Utility Model Registration] (1) Detecting the difference component between the audio signal and the ambient noise signal using a subtraction circuit, adding the difference component to an integrating circuit, and adding the difference component between the audio signal and the ambient noise signal to the magnitude of the ambient noise signal from the integrating circuit. The automatic volume adjustment device is configured to control a volume adjuster using a corresponding control signal, and the automatic volume adjustment device includes a first bandpass filter and a second bandpass filter for branching the audio signal, and a first bandpass filter and a second bandpass filter for branching the audio signal. a comparison circuit for comparing the outputs of the first and second bandpass filters, and a gate circuit controlled by the comparison circuit and for controlling the output of the subtraction circuit; An automatic volume adjustment device characterized in that the comparator circuit controls the operation of a gate circuit according to the difference. (2) Utility model registration claim 1, characterized in that the gate circuit is turned on by the comparison circuit only when the output difference between the first and second bandpass filters is equal to or greater than a certain value. Automatic volume adjustment device as described. (3) Claims 1 or 2 of the utility model registration claim, characterized in that the first and second bandpass filters are configured to pass mid-range components and high-range components of the audio signal, respectively. Automatic volume adjustment device as described.