Audio process units for controllably mixing L-channel and R-channel portions of a CD/CD-I audio signal each use a single attenuator (or digital multiplier) for developing L*G(LL), L*G(LR), R*G(RR) and R*G(RL) responses to L-channel and R-channel input signals through time sharing processing....http://www.google.de/patents/US5764775?utm_source=gb-gplus-sharePatent US5764775 - Audio processing unit for mixing L channel and R channel of CD/CD-1 audio signal 
