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Audio amplifier with gain controlled by ambient noise level - uses digital filtering system to measure and store ambient noise conditions
Audio amplifier with gain controlled by ambient noise level - uses digital filtering system to measure and store ambient noise conditions
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机译：增益由环境噪声电平控制的音频放大器-使用数字滤波系统来测量和存储环境噪声条件
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摘要
The amplifier is for audio systems which have to operate under conditions of high ambient noise, e.g. public address systems and audio equipment in vehicles or aircraft. The audio output level is automatically regulated according to ambient noise level to maintain a desired difference in volume. A microphone detects the ambient noise. Its output is applied to a band-pass filter which blocks all frequencies except those suppressed by a band block filter in the audio system input. The resulting signal is applied, after amplification, to a sample hold circuit. The latter passes a signal to the variable gain stage of the audio amplifier to adjust the output to the desired volume. The hold circuit is reset by a timer which also controls the cyclic application of the band block filter in the input to the audio amplifier. The actual value of the stored sample of background noise is thus continually updated. Below a background limit the timer and hold circuits are inactive. The use of digital circuit makes the proposed system practical.
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