Apparatus for synchronizing playback rates of a plurality of music sources includes a reference generator generating a reference signal including beats, a music source producing a music signal representative of music, a discriminating circuit operative in response to the music signal for extracting beats...http://www.google.com.tw/patents/US4594930?utm_source=gb-gplus-share專利 US4594930 - Apparatus for synchronizing playback rates of music sources
