Receiving reproducing system

• US 4,380,824 A
• Filed: 02/12/1981
• Issued: 04/19/1983
• Est. Priority Date: 04/18/1980
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Inoue, Takao
• Primary Examiner(s): Bookbinder, Marc E.
• Application Number:
  US06/233,869
• Time in Patent Office: 796 Days
• Field of Search: 179/1 P, 179/1 VE,1 VL, 455/235, 455/238, 455/246, 455/247, 455/297, 455/345, 455/212, 455/219, 455/155, 455/296, 455/142, 455/143
• US Class Current: 455/143
• CPC Class Codes: H03G 3/32 the control being dependent upon ambient noise level or sound level

Abstract

A receiving reproducing system for an automotive radio detects the surrounding noise level other than the output sound thereof, in the sound field extending in the passenger compartment of an automobile, and the level which is dependent upon the received signal level of an antenna. The receiving reproducing system partly controls its output sound volume proportionally in accordance with the surrounding noise level and partly lowers its output sound volume in dependence upon the reduction in the received signal level. Even under the circumstances where the surrounding noise level is high and where the received signal level is low, the sound volume of the output sound containing many noises can be prevented from being raised.

Claims

1. A receiving reproducing system comprising:

an antenna;

a signal processing circuit connected to said antenna for providing a detected output signal from a radio-frequency signal which is received by said antenna;

power amplifier means for amplifying the detected output signal of said signal processing circuit;

a speaker connected to be driven by said amplified output signal;

a variable gain circuit connected between said signal processing circuit and said power amplifier means;

noise detector means for detecting the surrounding noise level of a sound field;

received level detector means for detecting a level which is dependent upon the received signal level of said antenna; and

control means connected between said noise detector means and said variable gain circuit, said control means controlling the gain of said variable gain circuit in case the output signal of said received level detector means is higher than a preset value so as to control the level of said amplified output signal in proportion to the surrounding noise level of said sound field in response to the output signal of said noise detector means and said control means forcibly lowering the level of said amplified output signal in case said output signal of said received level detector means is lower than said preset value;

wherein said antenna includes an AM antenna and an FM antenna;

wherein said signal processing circuit includes an AM tuner for obtaining an AM detected output signal from an AM radio-frequency signal which is received by said AM antenna, an FM front end for obtaining an FM intermediate-frequency signal from an FM radio-frequency signal which is received by said FM antenna, an FM intermediate-frequency signal processing circuit for obtaining an FM detected output signal from said FM intermediate-frequency signal, and an FM stereo demodulator enabled to obtain a left-channel demodulated output signal and a right-channel demodulated output signal from said FM detected output signal;

wherein said power amplifier means includes a first power amplifier and a second power amplifier;

wherein said speaker includes a first speaker and a second speaker which are driven by the output signal of said first power amplifier and the output signal of said second power amplifier, respectively;

wherein said variable gain circuit includes a voltage-controlled attenuator having its signal transmission from a first input terminal to a first output terminal controllable by a control voltage, which is to be impressed upon a first control input terminal, and its signal transmission from a second input terminal to a second output terminal controllable by a control voltage which is to be impressed upon a second control input terminal, the first input terminal and the second input terminal of said voltage-controlled attenuator being selectively fed with either the AM detected output signal, which is obtained from said AM tuner, or the left- and right-channel demodulated output signal which are obtained from said FM stereo demodulator by way of a selection means, the first output terminal and the second output terminal of said voltage-controlled attenuator being connected with an input terminal of said first power amplifier and an input terminal of said second power amplifier, respectively;

wherein said received level detector means includes a tuning meter circuit in said AM tuner and a tuning meter circuit in said FM intermediate-frequency signal processing circuit;

wherein said control means includes a voltage comparator to be fed with a tuning meter drive voltage from one of said tuning meter circuits and a reference voltage which corresponds to said preset value wherein said control means further includes a change-over switch having a first input terminal connected to receive the output voltage of said noise detector means, a second input terminal connected to receive a control voltage for forced attenuation, and output terminals connected to the first and second control input terminals of said voltage-controlled attenuator; and

wherein the output of said voltage comparator controls said change-over switch, in case said tuning meter drive voltage is higher than said reference voltage, to impress the output voltage of said noise detector means upon the first and second control input terminals of said voltage-controlled attenuator, and impresses said control voltage for forced attenuation upon the first and second control input terminals of said voltage-controlled attenuator in case said tuning meter drive voltage is lower than said reference voltage, thereby disabling sound field effects on said power amplifier output signals.

2. A receiving reproducing system according to claim 1, wherein said noise detector means includes a microphone, a pre-amplifier for amplifying the output signal of said microphone, a subtraction circuit connected to receive the output signal of said pre-amplifier and an audio signal of one of said power amplifiers, a detector connected to the output of said subtraction circuit, and an integration circuit connected with the output of said detector, the output signal of said integration circuit being utilized as an output signal of said noise detector means.

3. A receiving reproducing system according to claim 1, wherein at least said antennas, said speakers and said noise detector means form a mobile unit.

4. A receiving reproducing system comprising:

an AM tuner for obtaining an AM detected output signal from an AM radio-frequency signal;

an FM front end for obtaining an FM intermediate-frequency signal from an FM radio-frequency signal;

an FM intermediate-frequency signal processing circuit for obtaining an FM detected output signal from said FM intermediate-frequency signal;

an FM stereo demodulator for obtaining a left-channel demodulated output signal and a right-channel demodulated output signal from said FM detected output signal;

a first terminal which can be supplied by way of a selection means with a selected one of said AM detected output signal and said left-channel demodulated output signal;

a second terminal which can be supplied by way of said selection means with a selected one of said AM detected output signal and said right-channel demodulated output signal;

a first voltage-controlled attenuator having an input terminal, a control terminal and an output terminal, the signal transmission from said input terminal to said output terminal being controllable by a control voltage impressed upon said control terminal and said input terminal being connected to said first terminal;

a second voltage-controlled attenuator having an input terminal, a control terminal and an output terminal, the signal transmission from said input terminal to said output terminal being controllable by a control voltage impressed upon said control terminal and said input terminal being connected to said second terminal;

a first power amplifier the input terminal of which is connected with said output terminal of said first voltage-controlled attenuator;

a second power amplifier the input terminal of which is connected with said output terminal of said second voltage-controlled attenuator;

a first speaker which is driven by the output signal of said first power amplifier;

a second speaker which is driven by the output signal of said second power amplifier;

noise detector means for detecting the surrounding noise level of a sound field;

received level detector means for detecting an AM level which is dependent upon said AM radio-frequency signal as well as an FM level which is dependent upon said FM radio-frequency signal, and

control means responsive to an output signal of said received level detector means and connected between the output terminal of said noise detector means and both of said control terminals of said first and second voltage controlled attenuator, said control means including means for transmitting the detected output of said noise detector means to both of said control terminals of said first and said second voltage controlled attenuator in case the output signal of said received level detector means is higher than a preset value so as to control said output signals of said first and second power amplifier proportionally in accordance with said surrounding noise level of said sound field and said control means forcibly lowering the level of said output signals of said first and second power amplifier in case said output signal of said received level detector means is lower than said preset value, thereby disabling sound field effects on said power amplifier output signals.

5. A receiving reproducing system according to claim 4, wherein said FM intermediate-frequency signal processing circuit includes audio mute control amplifier means for causing said FM detected output signal to become zero when the level of said FM intermediate-frequency signal is lower than a predetermined value.