|Media type||Vinyl record|
|Capacity||Four stereo channels|
|Read mechanism||phono cartridge|
|Developed by||Nippon/Columbia (Denon)|
Only 35 to 40 items are encoded in this format, and it was marketed only in the UK, Europe and Japan.
UD-4 is the process of modulating QMX onto a record with a process similar to CD-4, but also matrix encoded.
The system suffered from incompatibility with regular stereo playback due to phase differences between the left and right channels.
A BMX decoder could be used to play back UD-4 recordings, but, by adding a special cartridge and a UD-4 demodulator, two supplementary channels could be extracted and used to enhance directional resolution.
UD-4 systems first encoded the four original channels into four new channels. Two of these new channels contained the original four channels, matrix encoded. The other two contained only band-limited localization information, and were encoded with carriers similar to the CD-4 system.
UD-4 was less critical in its set-up than CD-4, because the carriers did not have to carry frequencies as high as those found in the CD-4 system.