Acoustic level limiting system for concerts and discotheques - uses microphone pick=up protected by ultrasonic reference signal

摘要

The audio signal force (1) is fed via a controllable attenuator and fixed gain amplifier (13) to the final amplifier (2). The output of a microphone (4) is amplified (7), rectified (8), amplified further (10) and used to control the attenuator (12). The output of an ultrasonic oscillator (6) is fed to a transducer (5), at least 2 metres from the microphone. The ultrasonic signal is amplified (9), detected and rectified (11) and used to increase attenuation if the ultrasonic signal is interrupted, e.g. by covering the microphone.