A Compatible Stereophonic System for the AM Broadcast Band

Stereophonic broadcasting presents a variety of problems, including compatibility, out-of-band radiation, stereo performance, distortion, signal-to-noise, receiver tuning, and receiver cost. Possible system solutions can be classified as either ``multiplicative'' or ``additive,'' depending upon whether the quadrature sidebands representative of the stereo information (L-R) are modulated by the envelope information (L+R), or are essentially independent of the envelope information, respectively. The preferred AM-FM system uses a pre-emphasized (L-R) signal to frequency modulate the carrier which is then amplitude modulated with (L+R). Stereophonic field test transmissions over Radio Station WNBC have demonstrated compatibility with existing monophonic receivers and excellent reception on stereophonic receivers of simple design.