Signal mutuality in stereo systems

Four stereo systems are compared: 1) 3 microphones, 3 independent transmission means or "tracks," and 3 speaker output or "channels," designated 3-3-3. 2) 3 microphones, 2 sound tracks and 3 outputs using a bridging or "derived" center channel, designated 3-2-3. 3) 2 microphones, 2 tracks, 3 outputs with derived center, designated 2-2-3. 4) A stereo microphone pair in a single housing with stereo separation derived by directional response of the 2 microphones, using 2 sound tracks and 3 play back speakers with derived center, designated SD-2-3 (SD for "stereo-directional" applied to the microphone) Each of the 4 systems is shown to contain mixtures of all signals in each channel. Crosstalk may be defined as the inadvertent transfer of a signal from one channel to another. Signal mutuality is the natural consequence of one microphone in a stereo array detecting signals pertinent to other microphones. The magnitude of differences between the 4 types of stereo studied are found to be small-of the order of less than 4 decibels. Delay effects are similar in the first 3 types, but where a single microphone location is used and dependence is on directional pattern for stereo separation, the delay effects are different. A separate study of the combined effects of sound delay and quality was made to corroborate the suspected delay effect of the so-called "stereo microphone."