Quadraphonic (or Quadrophonic and sometimes Quadrasonic)
It was a commercial failure due to many technical problems and format incompatibilities. Quadraphonic audio formats were more expensive to produce than standard two-channel stereo. Playback required additional speakers and specially designed decoders and amplifiers.
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Quadraphonic audio reproduction on vinyl records was problematic. Some systems used a
There were also less sophisticated "derived" solutions that only provided back ambience channels, not a defined placement of individual instruments. 
Quadraphonic systems based on tape were also introduced, based on new equipment capable of playing four discrete channels. These recordings were released in
A full, four-channel (quadraphonic) system will reproduce the Left Front, Left Back, Right Front, and Right Back audio signals in each of four separate speakers. Regardless of discrete or matrix formats, in four-channel stereo the rear speakers should be of the same or almost-same size or quality and have the same or almost-same frequency range as the front speakers.
Discrete reproduction is the only true Quadraphonic system. As its name suggests, with discrete formats the original four
With Matrix formats, the four channels are converted (encoded) down to two channels. These are then passed through a two-channel transmission medium (usually an LP record) before being decoded back to four channels and presented to four speakers. To transmit 4 individual audio signals in a stereo-compatible manner, there must be four simultaneous linear equations to reproduce the original 4 audio signals at the output. The term "compatible" indicates that:
The original systems (DY & EV-4) were basic and suffered from low front L/R separation (around 12db) and a poor rear L/R separation of 2db. The decoders were designed more to give an effect rather than accurate decoding, which was mainly due to limitations in both systems, although as both systems were very closely related mathematically, users only needed one decoder of either system to play back albums of both systems.
The aboves' poor decode performance was the main reason for their disappearance once the improved matrix systems arrived based on the work by
The differences between the original systems and the new were so large that it made it impossible to decode DY/EV-4 with either SQ or QS decoders with any accuracy, the results being just a form of artificial quad.
  This 4:2:4 process could not be accomplished without some information loss. That is to say, the four channels produced at the final stage were not truly identical to those with which the process had begun.
Derived (2-2-4) formats were inexpensive electronic solutions that provided back ambiance channels from regular stereo records. There was no deliberate placement of individual instruments on the back channels.