Editing Quadraphonic sound (section)

===Matrix (4–2–4) formats===
With matrix formats 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 to four channels and presented to four speakers. To transmit four individual audio signals in a stereo-compatible manner, there must be four simultaneous linear equations to reproduce the original four audio signals at the output.

These systems used [[matrix (sound recording)|matrix decoding]] technology to recover four channels from the two channels recorded on the record. Matrix systems can have a significant level of channel independence but not full channel separation.

*[[Stereo-4|EV / Stereo-4]] (1970)
*[[Dynaquad|DY / Dynaquad]] (used as an encoding format on some records) (1971)
*[[Stereo Quadraphonic|SQ / Stereo Quadraphonic]] (1971)
*[[QS Regular Matrix|QS (Quadraphonic Sound)/ RM (Regular Matrix)]] (1971)

Matrix quadraphonic recordings can be played in two channels on conventional stereo record players. There are varying levels of stereo and mono compatibility in these systems. The term ''compatible'' indicates that:
# A single-channel (mono) system will reproduce all four audio signals in its one speaker.
# two-channel (stereo) system will reproduce the left front and left rear audio signals in the left speaker and the right front and right rear signals in the right speaker.

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. In order for the effect to work as intended a recording engineer needed to be specially trained for working in each of these formats. Special mixing rules for matrix recording minimize the technological limitations inherent in matrix formats and mask or eliminate undesired side effects.

==== EV-4/Stereo-4 and Dynaquad (DY) ====

The first of these were basic systems with relatively poor performance developed by [[Electro-Voice]] (''[[Stereo-4|EV-4/Stereo-4]]'') and [[Dynaco]] (''[[Dynaquad|Dynaquad (DY)]]''). A so-called ''matrix'' format, it utilized four sound channels which were encoded into two stereo album tracks. These were then decoded into the original four sound channels. But with poor decode performance, these systems failed to match the accuracy or channel independence of later matrix formats.

The original systems (DY and EV-4) suffered from low front left-right separation (around 12&nbsp;dB) and a poor rear left-right separation of 2&nbsp;dB. The decoders were designed more to give an effect rather than accurate decoding, which was mainly due to limitations in both systems. Since both systems were very closely related mathematically, users only needed one decoder of either system to playback albums of both systems.

The differences between the early and late matrix systems were so vast, it made decoding DY/EV-4 with either SQ or QS decoders with accuracy impossible; the results often being a ''smeared'' or poorly defined sound stage, which could be vastly different from what was intended by the producer or recording engineer.<ref>{{cite journal
| last1        = Scheiber
| first1       = Peter
| author-link1  = Peter Scheiber
|date= December 1969
| title        = Toward a More Accurate Spatial Environment
| journal      = Journal of the Audio Engineering Society
| volume       = 17
| issue        = 6
| pages        = 690, 691
| publisher    = [[Audio Engineering Society]]
}}</ref><ref>{{cite journal
| last1        = Scheiber
| first1       = Peter
| author-link1  = Peter Scheiber
|date= November 1971
| title        = Analyzing Phase-Amplitude Matrices
| journal      = Journal of the Audio Engineering Society
| volume       = 19
| issue        = 10
| pages        = 835–839
| publisher    = [[Audio Engineering Society]]
}}</ref>

==== QS Regular Matrix and SQ Quadraphonic ====

[[File:Sansui QS-1 Synthesizer.jpg|thumbnail|Sansui QS sound decoder]]
Improved systems based on [[Peter Scheiber]]'s work on utilizing 90-degree phase-shift circuitry came later, namely the ''[[QS Regular Matrix|QS]]'' and ''[[Stereo Quadraphonic|SQ]]'' systems.

The first of these, known as ''QS'', was developed by [[Sansui Electric]]. A so-called matrix format, it utilized four sound channels, which were encoded into two stereo album tracks. These were then decoded into the original four sound channels. The QS system debuted in the United States in March 1971 and was improved by their ''Vario-Matrix'' system in 1973.{{Citation needed|date=January 2012}}

The second, ''SQ'', was developed and marketed by [[Columbia Records]] and [[Sony]] and entered the US market in April 1971. The ''SQ'' format was also used by companies such as [[EMI]] in Great Britain, who pressed several ''SQ'' album releases. The sound separation of the ''SQ'' system was greatly improved by the introduction of ''SQ Full Logic'' decoding in 1975 using the Motorola chips MC1312, MC1314 & MC1315.<ref>{{Cite web|url=https://datasheetspdf.com/pdf/570327/Motorola/MC1312P/1|title = MC1312P SYSTEM Datasheet PDF - DECODER SYSTEM. Equivalent, Catalog}}</ref>

Both SQ and QS had significant support from major record companies and hardware manufacturers during the 1970s. They also achieved notable sales and market penetration. Unfortunately, due to the similarities in name and technology these could easily be confused by the public.