Quad Tape, either 8 Track or Reel, and CD-4 LPs are the only discrete legacy quad systems. With these 3 formats, the 4 channels remain separate throughout the entire audio route from the playback source to the speakers.
SQ, QS, RM, DY, etc, the 'matrix' systems, which could be used on LP, tape, cassette, or any other medium, take the 4 independant channels, encode them to stereo, then put them on an LP or tape or whatever as a standard 2 channel stereo track. When played back on a 2 Channel playback device, a matrix decoder then takes the encoded stereo audio, which is really the ixed up 4 channels crammed into 2 channels, and attempts to split them back into the 4 original channels. No matter how good the encoder and decoder were, in the 1970's, the 4 channels would never and could never be again totaly separated to the point that they were before they were encoded. In the late '70s, improved SQ decoders were sold (Tate, Audionics, etc), but the source material still suffered from the limitations of the early matrix encoders. You could never improve the encoding without reissuing all of the released titles again using a new improved encoder. That never happened.
So, not considering the audio playback fidelity, (because an SQ LP obviously will have better audio fidelity than an 8 track tape), the matrix systems never gave the listener "quad" that was as good as the discrete systems. It was the nature of the beast.
The following visual example of the Dark Side of the Moon saga on Q8 shows what I mean. The US Q8 was sourced with a decoded martrix mix, while the UK Q8 was totally discrete
SQ, QS, RM, DY, etc, the 'matrix' systems, which could be used on LP, tape, cassette, or any other medium, take the 4 independant channels, encode them to stereo, then put them on an LP or tape or whatever as a standard 2 channel stereo track. When played back on a 2 Channel playback device, a matrix decoder then takes the encoded stereo audio, which is really the ixed up 4 channels crammed into 2 channels, and attempts to split them back into the 4 original channels. No matter how good the encoder and decoder were, in the 1970's, the 4 channels would never and could never be again totaly separated to the point that they were before they were encoded. In the late '70s, improved SQ decoders were sold (Tate, Audionics, etc), but the source material still suffered from the limitations of the early matrix encoders. You could never improve the encoding without reissuing all of the released titles again using a new improved encoder. That never happened.
So, not considering the audio playback fidelity, (because an SQ LP obviously will have better audio fidelity than an 8 track tape), the matrix systems never gave the listener "quad" that was as good as the discrete systems. It was the nature of the beast.
The following visual example of the Dark Side of the Moon saga on Q8 shows what I mean. The US Q8 was sourced with a decoded martrix mix, while the UK Q8 was totally discrete