Matrix encoder with improved channel separation

An encoder for use in a surround sound system wherein at least four audio input signals (FL, FR, RL, RR) representing an original sound field are encoded into two channel signals (L, R) and said encoded two channel signals are decoded into at least four audio output signals (FL′, FR′, RL′, RR′) corresponding to said four audio input signals, said encoder including:

• matrix means connected to receive said four audio input signals for encoding said four input signals into two channel (L and R) output signals, said matrix means including means responsive to said four input signals for producing Lenc and Renc output signals as follows:
• Lenc=FL+kFR+jRL+jkRR
• Renc=FR+kFL−jRR−jkRL
• wherein k denotes a transformation or matrix coefficient having a value that is steered dynamically based on level of rear signal (RL+RR) content relative to front signal (FL+FR) content.

An encoding method for use in a surround sound system wherein at least four audio input signals (FL, FR, RL, RR) representing an original sound field are encoded into two channel signals (L, R) and said encoded two channel signals are decoded into at least four audio output signals (FL′, FR′, RL′, RR′) corresponding to said four audio input signals, said method including:

• processing said four audio input signals into two channel (L and R) output signals by matrix means responsive to said four input signals for producing Lenc and Renc output signals as follows:
• Lenc=FL+kFR+jRL+jkRR
• Renc=FR+kFL−jRR−jkRL
• wherein k denotes a transformation or matrix coefficient having a value approximately 0.207 and j denotes a 90 degree phase shift.

An encoding method for use in a surround sound system wherein at least four audio input signals (FL, FR, RL, RR) representing an original sound field are encoded into two channel signals (L, R) and said encoded two channel signals are decoded into at least four audio output signals (FL′, FR′, RL′, RR′) corresponding to said four audio input signals, said method including:

• processing said four audio input signals into two channel (L and R) output signals by matrix means responsive to said four input signals for producing Lenc and Renc output signals as follows:
• Lenc=FL+kFR+jRL+jkRR
• Renc=FR+kFL−jRR−jkRL
• wherein k denotes a transformation or matrix coefficient and wherein said processing includes steering the value of coefficient k based on level of rear signal (RL+RR) content relative to front signal (FL+FR) content.