A system (130) for providing enhancement to a voice-band signal in a telecommunications network (138) is provided. The present system (130) includes a power averager (18) for determining the average power of the voice-band signal. The present system (130) also includes an equalizer (132) for attenuating a predetermined portion of the voice-band signal and an output scaler (134) for scaling the equalized voice-band signal with a scaling factor. The system (130) of the present invention also includes an automatic gain enhancer (136) for applying an automatic gain factor to the scaled voice-band signal and wherein the automatic gain factor is dependent upon the average power of the input voice-band signal.

Voice enhancement system and method

A loudspeaker protection circuit senses an overload condition caused by an improper input signal or a fault within the amplifier by sensing a DC or infrasonic signal applied to the loudspeaker. The time between zero (axis) crossings of the amplifier output signal, which are related to the lower frequency components of the signal, are detected. If the period of time between zero crossings exceeds a predetermined time limit, the supply of the amplifier output signal to the loudspeaker is interrupted. In order to prevent false tripping of the circuit by normal conditions, the circuit only responds to signals exceeding a predetermined voltage level.

Loudspeaker protection circuit

An audio system including audio processing circuit means interposed between a source of audio signals and a power amplifier. Power control circuitry including time delay means which respond to an on/off power switch for applying and removing power to the components of the audio system in a sequence which prevents audible pops associated with system start-up and shutdown.

Audio system with orderly shutdown sequence

In an audio amplifier, a ripple removing filter capacitor (C9) is connected to a ripple terminal (7), and a negative feedback capacitor (C8) is connected to a negative feedback terminal (6). A pop noise suppression circuit of the amplifier has a forcible discharging circuit (15) which is not operated in a steady state of the audio amplifier. The forcible discharging circuit is operated to forcibly discharge residual charges on the ripple removing capacitor (C9) and the negative feedback capacitor (C8) only when a power supply (Vcc) of the audio amplifier is turned off.

Pop noise suppression circuit for audio amplifier

A sound system comprises a source of program material, a transducer coupled to the source to produce an audible signal related to the program material, a controllable bass contour control network having a control terminal, a power amplifier, a second transducer and a low pass filter. The controllable bass contour control network is coupled to the program material source. The power amplifier is coupled to the controllable bass contour control network. The second transducer and the low pass filter are coupled to the power amplifier. The low pass filter is coupled to the control terminal of the controllable bass contour control network. The output of the lower pass filter controls the contour of the signal supplied from the program material source through the controllable bass contour control network to the power amplifier based upon the signal provided by the power amplifier to the low pass filter. The control terminal comprises a terminal of a light sensitive resistor. The low pass filter further comprises a light emitting device. The low pass filter is coupled to the control terminal of the controllable bass contour control network by coupling light from the light emitting device to the light sensitive resistor.

Automotive sound system

A muting circuit for loudspeakers is operable to disconnect a loudspeaker from an amplifier immediately upon a power supply being interrupted. The muting circuit includes an around-zero-volt detection circuit for detecting around the zero volt level of a commercial AC voltage. An RC time constant circuit is controlled by the output of the around-zero-volt detection circuit to either charge or discharge the capacitor in the RC time constant circuit only when the around zero volt level is detected. A threshold circuit is connected to the RC time constant circuit and operates a loudspeaker relay when the charge on the capacitor either exceeds or decreases below a predetermined level.

Akio Ozawa

Papers

Muting circuit for loudspeaker