Patent ID: 8045719

Claim:
A method for deriving three channels, a left channel, a center channel, and a right channel from two, left and right, stereophonic channels, comprising deriving the left channel from a variable proportion of the left stereophonic channel, deriving the right channel from a variable proportion of the right stereophonic channel, and deriving the center channel from the combination of a variable proportion of the left stereophonic channel and a variable proportion of the right stereophonic channel, wherein each of said variable proportions is determined by applying a gain factor to the left or right stereophonic channel, the gain factors being derived by determining the difference in a measure of the sound that would be present at the ears of a listener centrally-located with respect to a configuration according to a first model in which the stereophonic channels are applied to left and right loudspeakers and with respect to a configuration according to a second model in which the stereophonic channels are applied to left and right loudspeakers and to a center loudspeaker, and controlling, with gain factors, the proportion of the stereophonic channels applied to the left, center and right loudspeakers in said second model to minimize said difference while simultaneously causing a portion of the left and/or right stereophonic channels to be applied to the center loudspeaker under some conditions of the signals in the two stereophonic channels, the portion being commensurate with the value of a weighting factor, such that the weighting factor controls a balance between two opposing conditions, one in which no signals are applied to the center loudspeaker and another in which no signals are applied to the left and right loudspeakers.