Any discussion about music and sound reproduction will eventually make reference to how it is presented to the listener. Of course, it all began with monophonic, but over the years technology has provided more and more choices starting with stereophonic, followed by a host of multi-phonic formats like quadraphonic, Dolby 5.1 and 6.1. Monophonic (mono) has just one prerecorded channel. Stereophonic sound (stereo) has two distinct channels, left and right.
Finally let me touch upon quadraphonic recordings as they appeared on vinyl records. There was no industry standard when it came to defining exactly what quadraphonic was, so many different types of quadraphonic techniques and their resulting consumer products appeared on the market.