The Orban Stereo Synthesizer processes any monophonic sound source into pseudo-stereo quickly and easily. The pseudo-stereo does not degrade the quality of the mono recording, and possesses many attributes of true stereo, such as depth, space, directionality, stability, and good channel balance. Mono compatibility is assured by the following facts: 1] The electrical sum of the two output channels is proportional to the mono input to the Synthesizer; and 2] The sum of the left and right powers (as a function of frequency) is proportional to the power in the mono input. [1] means that a listener can recover the original mono by summing the two stereo channels together. This removes many "purist" objections to pseudo-stereo, since the purist can choose freely between pseudo-stereo and the original mono. It also means that mono FM listeners will hear the original mono source when listening in mono to a stereo FM station. [2] means that the acoustical frequency balance of the pseudo-stereo is identical to the frequency balance of the mono. Both [1] and [2] hold for any adjustments of the Stereo Synthesizer operating controls.