A radio frequency (RF) base station transmitter receiver (transceiver) system includes an audio compression arrangement that compresses a sum of multiple audio signals so that all signals within the sum are equalized to a substantially uniform audio output level despite differences in their input levels....http://www.google.com.hk/patents/US5241689?utm_source=gb-gplus-share專利 US5241689 - Digital signal processor audio compression in an RF base station system
