UD-4

{{Short description|Discrete 4-channel quadraphonic gramophone record format developed by Nippon Columbia}}

{{Infobox media

| title = UD-4

| name = UD-4

| logo = UD-4_format_logo.png

| image =

| caption = UD-4 logo

| type = Phonograph record

| encoding = Analog signal

| capacity = Four audio channels

| read = phono cartridge

| write =

| standard =

| owner = Nippon/Columbia (Denon)

| use = Audio storage

| extended from =

| extended to =

| released = 1974

}}

UD-4{{Cite news |last=Hope |first=Adrian |date=April 10, 1975 |title=Two more innovations for the hi-fi addict |pages=81 |work=New Scientist |url=https://books.google.com/books?id=u1DJomI318MC&dq=BMX+quadrasonic%2C+two+channel+matrix&pg=PA81}}{{Cite news |last1=Cooper |last2=Takagi |date=March 1975 |title=THE UD-4 SYSTEM |work=Hi-Fi News & Record Review |url=https://www.quadraphonicquad.com/QQ-ud4_hifi.htm}} was a discrete four-channel quadraphonic sound system for phonograph records introduced by Nippon Columbia{{Cite journal |last=Myers |first=Alfred |date=May 1978 |title=FCC's 4-Channel Listening Tests |url=https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/70s/Audio-1978-05.pdf |journal=Audio |pages=24}} (Denon) in 1974. This system had some similarities with the more successful CD-4 process introduced by JVC and RCA in 1972.

Only about 35 to 40 LP album titles were encoded in this format, and it was marketed only in the UK, Europe and Japan. Most of these releases were marketed by the Denon label.

The UMX (universal matrix){{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=AES}} standard used for UD-4 contains two subsystems:

• BMX (quadrasonic, two channel matrix),{{Cite patent|number=US4152542A|title=Multichannel matrix logic and encoding systems|gdate=1979-05-01|invent1=Cooper|inventor1-first=Duane P.|url=https://patents.google.com/patent/US4152542A/en}}{{Cite journal |last=Gerzon |first=Michael |date=December 1974 |title=Surround-sound psychoacoustics |url=http://www.angelofarina.it/Public/Soundfield/wireless-world-gerzon-12-1974.pdf |journal=Wireless World |pages=483}}{{Cite book|url=https://books.google.com/books?id=hBJJCAAAQBAJ&dq=BMX+quad+matrix&pg=PT147|title=Handbook of Recording Engineering|first=John M.|last=Eargle|date=December 6, 2012|publisher=Springer Science & Business Media|isbn=9789401093668 |via=Google Books}} a basic 4-2-4 matrix decoder (different from QS Regular Matrix);
• QMX (four channel matrix), a discrete 4-4-4 system (adding band-limited localization information encoded with high frequency carrier signals similar to the CD-4 system).{{Cite web |last=Robinson |first=Larry |title=Quadraphonic Systems |url=https://midimagic.sgc-hosting.com/quadrafon.htm |access-date=2023-01-12 |website=MidiMagic}}

The UD-4 process modulated both BMX and QMX into a single record. This way, a BMX decoder could be used to decode quadraphonic sound using an existing stereo record player, while by using a special phono cartridge and a specialized UD-4 demodulator discrete supplementary QMX channels could be extracted (enhancing directional resolution).

In theory this allowed backward compatibility with existing players and records, but the system suffered from incompatibility with regular stereo playback due to phase differences between the left and right channels.{{Cite journal |last1=Cooper |first1=Duane |author-link=Duane H. Cooper |last2=Takagi |first2=Toshihiko |date=March 1975 |title=THE UD-4 SYSTEM |url=https://www.quadraphonicquad.com/QQ-ud4_hifi.htm |journal=Hi-Fi News & Record Review}}

Phono cartridge set-up for UD-4 playback was less critical than in CD-4, because the high frequency carrier signals were not as high as those found in the CD-4 system.