Duophonic

For the record company of the same name, see Duophonic Records. For the album by Charles and Eddie of the same name, see Duophonic (album).

• In synthesizers, capable of sounding two voices, or notes, at a time. Compare: monophonic, polyphonic.

• Duophonic is also a term used to refer to a sound process by which a monaural recording is turned into a kind of "fake stereo" by splitting the signal into two channels, delaying the left and the right channels by means of delay lines and other circuits, desynchronizing the two channels by fractions of a second, and cutting the bass frequencies in one channel with a high-pass filter, then cutting the treble frequencies in the other channel with a low-pass filter. The end result was a synthesized stereo effect, without giving the listener the true directional sound characteristics of real stereo. In some cases, the effect was enhanced with reverb and other technical tricks, sometimes adding stereo echo to mono tracks in an attempt to fool the listener.

"Duophonic" was used as a trade name for the process by Capitol Records for re-releases of mono recordings from June of 1961 through the 1970s. Capitol employed this technique in order to increase their inventory of stereo LPs, to satisfy retailer demand for more stereo content (and help promote the sale of stereo receivers and turntables). For nearly ten years, Capitol used the banner "DUOPHONIC-For Stereo Phonographs Only" to differentiate their true stereo LPs from the Duophonic LPs.

The process was used for some of their biggest releases, including a variety of albums by The Beach Boys and Frank Sinatra. Over the years however, some Duophonic tapes were confused with true stereo recordings in Capitol Records' vaults, and wound up getting accidentally reissued on CD throughout the 1980s and 1990s. In recent years, Capitol reissued some of The Beatles' Duophonic mixes on The Capitol Albums, Volume 1 and The Capitol Albums, Volume 2, in 2004 and 2006, respectively.

Other record companies used similar processing of monophonic material to create a stereo effect, but referred to the process by other names. For example, Columbia Records used the logo, "Electronically Re-channeled for Stereo" on records issued with their particular process. As with Capitol, Columbia's fake stereo issues included albums by major artists, such as Miles Davis ('Round About Midnight-CL 949 mono, reissued in stereo as PC 8649).

External links

• The "Arcane Radio Trivia" blog on Duophonic recordings