Stereo decoder

Extracting the separate left hand and right-hand signals from a multiplexed stereo signal is a complex process. It requires an auxiliary carrier of exactly the same frequency (38 kHz) and phase as that in the transmitter. A voltage-controlled oscillator (VCO) by itself is not good enough. It needs to be synchronized with the 19 kHz pilot tone in the multiplexed (MPX) signal. Furthermore, a mono / stereo converter controlled by the pilot tone, preferably with an optical indicator, is required.