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UD-4, also known as UMX or BMX, was a discrete 4-channel quadraphonic sound system 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. The UMX standard contains two subsystems, BMX, a basic 4-2-4 encoded matrix (different from Regular Matrix), and QMX, a 4-4-4 system. 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. == References == 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「UD-4」の詳細全文を読む スポンサード リンク
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