SURROUND-SOUND DECODERS - 1, 2.

The Compatible Discrete 4 system (CD-4) was developed to allow four separate signals to be recorded on a disc record, at the same time having playback capability in stereo and mono when played through existing equipment. The principles of recording and playback of this system are discussed in the first part of this article. A circuit of a CD-4 demodulator is presented that is intended for constructing a CD-4 unit. Part Two of the article gives the values of the circuit components and provides performance details of the decoder. An IC is utilized which includes preamplifier, phase-locked loop demodulator, expander, and mating circuits. Spectrum analyzer traces show the performance of the record-cartridge-decoder system for various extended-response phonograph pickup cartridges.