SYNTHESIZED FOUR CHANNEL STEREO FROM A TWO CHANNEL SOURCE

This invention relates to a synthesized four channel output from a two channel stereo source. The invention operates on left and right ((L), (R) input signals to produce difference signals (L-R), (R-L) by combining a left signal with a phase shifted right signal and by combining a right signal with a phase shifted left signal. The amount of phase shift introduced on each phase shifted signal is frequency dependent and varies from 0 DEG -180 DEG with low frequency components being 180 DEG out of phase and the high frequency components substantially in phase. In addition another phase shift is introduced on at least one difference signal, to place a phase shift of less than 90 DEG between the two difference signals. The two difference signals are then fed to the rear speakers in a four channel reproduction system.