Editing Quadraphonic sound (section)

===Discrete (4–4–4) formats===
'''Discrete reproduction''' describes a quadraphonic system in which all four channels are fully independent of each other. As its name suggests, with ''discrete'' formats the original four [[audio channel]]s are passed through a four-channel transmission medium and presented to a four-channel reproduction system and fed to four speakers. This is defined as a 4–4–4 system.

*[[Compatible Discrete 4|CD-4 (Compatible Discrete 4) / Quadradisc]] (1972)
*[[UD-4|UD-4 / UMX / BMX]] (1974)

Discrete phonograph systems use a specialized [[demodulation|demodulator]] to decode four fully independent sound channels. This allowed for full channel separation. Such systems could be prone to reduced record life. However, more durable vinyl formulations were quickly developed to work around this problem and nearly all discrete LPs use special vinyl. When discrete quadraphonic LPs are played on conventional stereo record players the entire music program can be heard in stereo.

==== CD-4 or Quadradisc ====

[[File:QuadraDisk.jpg|thumbnail|An RCA Quadradisc record]]

The third major format for four-channel vinyl LPs, known as ''[[Compatible Discrete 4|CD-4]]'' or ''[[Compatible Discrete 4|Quadradisc]]'', was devised by the Japanese [[JVC]] Corporation along with its US counterpart [[RCA Records]].

This quadraphonic format was first marketed in the United States in May 1972. A fully discrete system, it eschewed matrix technologies in favor of a method similar to the encoding of [[FM broadcasting#Stereo FM|stereo FM]] broadcasts.  With stereo records, the system uses 2 main left and right audio channels, and this is what allows CD-4 to maintain compatibility with conventional stereo playback. CD-4 also adds 2 additional ''difference'' audio channels to the main channels. The difference signals are encoded in [[Ultrasound|ultrasonic]] carrier frequencies in the range of 30&nbsp;kHz, which is above the audible range. CD-4 requires a specialized [[Magnetic cartridge|phono cartridge]] with a [[Shibata stylus]] to read these additional high frequencies. The combined signals are then sent to a special demodulator for four-channel decoding. The demodulator converts the ultrasonic signals back into the audible range and uses the difference channels to separate rear audio information from the main channels. Because the CD-4 system maintains four independent signals throughout the process it can accurately reconstruct the intended four-channel sound field.

==== UD-4 / UMX / BMX ====

''[[UD-4|UD-4/UMX]]'' was developed by Nippon/Columbia ([[Denon]]). This is a hybrid discrete/matrix system. Only 35 to 40 items are encoded in this format and it was marketed only in the UK, Europe, and Japan.

The short-lived system suffered from incompatibility with regular stereo playback due to phase differences between the left and right channels.<ref>{{cite magazine |last=Cooper |first=Duane |author-link1=Duane H. Cooper |title=The UD-4 System |url=http://www.quadraphonicquad.com/QQ-ud4_hifi.htm |magazine=Hi-Fi News & Record Review – March 1975 |access-date=5 February 2012}}</ref> UD-4 was less critical in its setup than CD-4 because the carriers did not have to handle frequencies as high as those found in the CD-4 system.<ref>{{cite journal |last1=Cooper |first1=Duane H. |author-link1=Duane H. Cooper |last2=Shiga |first2=Takeo |title=Discrete-Matrix Multichannel Stereo |url=http://decoy.iki.fi/dsound/ambisonic/motherlode/source/Discrete_Matrix%20Multichannel%20Stereo%20Duane%20Cooper%201971.pdf |access-date=September 28, 2018 | journal=Journal of the Audio Engineering Society |volume=20 |issue=5 |pages=346–360 |date=June 1972 |publisher=[[Audio Engineering Society|AES]]}}</ref>