JPS5923644A - Stereophonic signal reproducing circuit - Google Patents

Abstract

PURPOSE:To prevent an increase in discomfort noise by stopping the functions of a sound field controlling circuit automatically when a weal signal or multipath disturbing wave is received. CONSTITUTION:The sound field controlling circuit 17 is so controlled by the output of a signal intensity detector 19 or multipath detector 20 so that its internal switch 18 is turned off. When the extent of disturbance increases up to a specific value, the detector 10 sends out the OR output of an OR circuit 21 and when a weak signal is received, on the other hand, the signal intensity detector 19 sends out the OR output of the circuit 21. Consequently, the switch 18 controlled by the OR output of detector 19 or 20 is turned on in response to an increase in discomfort noise generated by the sound field controlling circuit during weak signal or multipath disturbance reception to stop the sound field controlling functions forcibly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a stereo signal reproducing circuit in which a sound field control circuit is added between a stereo demodulator and a low frequency amplifier to perform sound field control during stereo reception.

1. Configuration of conventional example and its problems FIG. 1 is a block diagram for explaining a conventional sound field control circuit.

In Figure 1, left and right stereo signals are shown, R is terminal 1,
2 to each adder 3, 4, and is added to the difference signal generation circuit 6, where the difference signal (L-
R) and is converted into a constant delay time m by the delay circuit 6.
only delayed. The output of this delay circuit 6 is then applied to a coefficient circuit 7 having a gain coefficient K, and further the coefficient circuit 7
The output of 0 is applied to the phase inversion signal generation circuit 8 and output as difference signals 9 and 10 with mutually opposite phases.The difference signal 9.10 at this time is K(L-R)m...・・・
(1) K(R-L)m ・・・・・・
... (2), and these are added to adders 3 and 4, respectively. Therefore, the output signals of adder 3.4 are respectively L+K(L-R)m =-- (3)
R+K(R-L)m ・・・・・・・・・
(It can be expressed as a grape.Then, equation (3), (4)
The output signals of adders 3 and 4 expressed by the equations are respectively amplified by low frequency amplifiers 11.12 and applied to speakers 13.14. Therefore, the speaker 13 outputs a sound corresponding to the output signal expressed by equation (3), and the speaker 14
, a sound corresponding to the output signal expressed by equation (4) is output. Here, the gain coefficient K in equations (3) and (4)
It is well known that by setting the delay time m to an appropriate value, it is possible to widen the stereo sound and further enhance the stereo effect, and it is widely used for stereo signal reproduction in tape recorders.

However, when the above-mentioned sound field control circuit is used for stereo signal reproduction in a receiver such as FM stereo broadcasting, noise is superimposed on the left and right channel stereo signals and R when receiving a weak signal or receiving a multipath interference wave. Therefore, each difference signal 9, 1 of the phase inverted signal generation circuit 8
When adding 0 to each adder 3゜4, equation (1), (
As is clear from the above formula, there was a problem in that the noise component increased and the sound quality deteriorated significantly when reproducing nine stereo signals.

Purpose of the Invention The present invention is intended to eliminate the above-mentioned drawbacks of the prior art, and to provide an excellent reproduction state at all times without increasing unpleasant noise even when receiving weak signals or receiving multipath interference waves. The purpose is to

Structure of the Invention The present invention provides a sound field control circuit composed of a difference signal generation circuit, a delay circuit, an adder, etc. between a stereo demodulator and a low frequency amplifier, and the function of this sound field control circuit is to detect weak signals. It is configured to automatically stop when receiving multipath interference waves.

DESCRIPTION OF THE EMBODIMENT FIG. 2 is a block diagram of an embodiment of the present invention.

In the figure, 15 is an FM detector, 16 is a stereo demodulator, and 17
is a sound field control circuit, except that a switch 18 is connected between the coefficient circuit 7 and the phase inversion signal generation circuit 8.
This is the same configuration as shown in the figure. As is clear from the figure, the sound field control circuit 17 is controlled to cut off the switch 18 using either of the outputs of the signal strength detector 19 and the multipath detector 20.

Here, the multipath detector 20 detects (1) the amplitude modulation level of the intermediate frequency signal, (2) the amplitude modulation level of the pilot signal in the detected signal, (3) the harmonic level outside the composite signal band in the detected signal, etc. A detection circuit can be used. and multipath detector 2o
is set to output an OR output from the OR circuit 21 when the degree of interference increases to a predetermined value, and on the other hand, the signal strength detector 19 is set to output an OR output from the OR circuit 21- when the signal is weak. The increase in harsh noise caused by the sound field control circuit when receiving a weak signal and when receiving multipath interference is forcibly suppressed by shutting off the switch 18 controlled by the OR output of the signal strength detector 19 and the multipath interference detector 2o. This stops the arc sound field control function. As a result, the auditory sense of noise can be greatly reduced.

In the embodiment shown in FIG. 2, the switch 18 for stopping the sound field control function is connected to the coefficient circuit 7 and the phase inversion signal generation circuit 80.
However, the same effect can be achieved by inserting the signal anywhere in the signal path from the difference signal generation circuit 6 to the adders 3 and 4.

Effects of the Invention As is clear from the above embodiments, according to the stereo signal reproducing circuit of the present invention, the sound field control circuit is configured to automatically stop its function when a weak signal is received and when a multipath interference wave is received. Therefore, there is no increase in unpleasant noise even when receiving a weak signal or receiving multipath interference, which is extremely advantageous in practice.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional sound field control circuit, and FIG. 2 is a block diagram of an embodiment of the stereo signal reproducing circuit of the present invention. 3, 4... Addition circuit, 6... Difference signal generation circuit, 6... Delay circuit, 7... Coefficient circuit, 8... Phase Inverted signal generation circuit, 15...
...FM detector, 16...Stereo demodulator, 1
7...Sound field control circuit, 18...Switch, 19...Signal strength detector, 2o...
・Multipath detector, 21...OR circuit.

Claims (1)

[Claims] A sound field control circuit consisting of a difference signal generation circuit, a delay circuit, an adder, etc. is connected between the stereo demodulator and the low frequency amplifier, and a switch circuit is installed within the sound field control circuit to detect weak signals. , a received signal strength detector that outputs a predetermined signal when receiving a multipath interference wave, and an FM multipath interference detector that controls the above switch circuits on and off according to the output signals, respectively, when receiving a weak signal and when receiving a multipath interference wave. A stereo signal reproduction circuit configured to stop the function of the sound field control circuit.