Abstract: The decoding circuit of the present invention is a passive circuit which connects to the output terminals of a conventional stereophonic amplifier for decoding additional hidden channels of sound from a stereophonic or quadraphonic source. The circuit couples power from the two existing channels so as to provide additional output points at prescribed polarity and voltages to produce new and separate channels of sound. Capacitive reactance is utilized in the circuit to cause lagging voltages to produce a desirable phase shift while a variable impedance is provided to control the volume of the additional channel speakers relative to the existing speakers.