Quadraphonic technology involves using four-track stereo (rather than traditional two-track). This technology places two sound sources in front and two in the rear of the listener, creating a "surround" effect. Each track is completely independent of the others, meaning that the normal "bouncing back" sound of two channels is replaced with two new channels. Quadraphonic technology should not be confused with surround sound technology, which is essentially two-track stereo recording rechanneled electronically into more tracks.
There are essentially two methods used in recording quadraphonic sound sources. The first method places two microphones at the rear of a recording hall or studio during a session, so that reverberation of primary sound is picked up.. When playback occurs, a "live" sense is felt by the listener. The second method employs equal sound sources in all directions, so that twice as much separation can be obtained.
Recording in quadraphonic sound is relatively simple on magnetic tape. Multiple tracks have long been common, so transference to four-track sound is easily achieved with the proper equipment. Disc recording is much more complex. The matrix system involves phasing four channels onto a two-channel stereo disc. Decoders in the equipment detect the four separate channels and send the signals to the appropriate speakers. The discrete system involves a supersonic signal being cut into the groove along with each channel. A special stylus reads this signal, and a decoder combines the signal with the standard signal to recreate four channels.
Since quadraphonic technology requires advanced and expensive decoding equipment, it has not been a great commercial success. Surround technology has been much more successful for the commercial market.
Surround technology is different from quadraphonic technology
in that it is independent of the technology used to master the recording.
The equipment takes the signals from each channel and remixes them through
an equalizer. The new signals are then sent to a variety of other
speakers to produce a surround effect when the speakers are arranged on
all sides of the listener. Surround technology may add echo, or may
highlight certain aspects of the recording, such as tone or bass.