Patent ID: 8605914

Claim:
An audio processing circuit comprising: an input adder and an input subtractor adapted to receive an input stereo signal and to provide a sum signal and a difference signal respectively a center sound detector, comprising: a first envelope follower applied to the sum signal and a second envelope follower applied to the difference signal; a gain computation module adapted to compute an unsmoothed gain signal in accordance with conditions when EM≠0 and ES=0, then Gx˜0, where the .computed gain is Gx, and EM and ES are the sum and difference envelope signals respectively at the input to the gain computation module; and when EM≠0 and abs(EM).=abs(ES), then Gx=1 from outputs of said first and second envelope followers; and a smoothing filter adapted to smooth the unsmoothed gain signal, giving rise to a smoothed control gain; and a variable output 3×2 matrix Mat(Gc) controlled by said smoothed control gain and adapted to provide an output stereo signal and an output mono center signal based on said sum and difference signals.