Quadraphonic Sound
Quadraphonic is a term used in audio technology to refer to a four discrete source signal format. To make this clear consider the stereophonic high fidelity sound system. Stereos sound-systems are characterized by having two speakers that produce sound from two independent source signals recorded onto a single format. These days the format is primarily CDs and MP3 players, in the not so distant past the formats were vinyl records and magnetic tape. A sound recordist making a recording to be mixed to stereo would place each of the signals from a source recording in either the left speaker or the right speaker or some combination of the two. 
This is a great jump in spatial perception, on the part of the listener, compared to monophonic recording mediums and playback systems. Stereo is truly the end in perceivable aural experience. But to truly experience the maximum result and definition or perception that is possible with a stereo system a very well design amplifier and speaker system must be employed not to mention a custom built finely tune room designed specifically for the use of the speakers and amplifier, and in some cases the format, that will be used in the room. This type of setup can run into the hundreds of thousands of dollars to acquire. So, it is out of reach for most of us who really enjoy well recorded sound. However, quadraphonic sound systems can provide a remarkable aural experience for not much more than a pair of good stereo systems cost. In the end that is just what a quadraphonic sound system is two stereo systems. One stereo pair in front and one stereo pair in back so there are four discrete sound sources.
Source media for quadraphonic is rare. Some what popular in the seventies Quadraphonic enjoyed vinyl records and 1/4" magnetic tape as mediums. The vinyl came in a couple of general flavors. One CD-4 Quadradisc required a special stylus used a 30KHz carrier signal (which means the embeded rear channels only resolved up to 15KHz) The other types of qudraphonic vinyl used normal stylists but made use of a phase matrix to encode the extra channels. ut even the phase matrix required a decoder to separate the the extra channels which were encoded into the normal stereo pair. Tape came in two main consumer forms both were 1/4". They were the cartridge and the open reel formats. The cartridge was basically an eight track cartridge that doubled up the play back channels. There were still eight tracks on the tape but instead of four selections of stereo, there were two selections of quadraphonic. This meant if you were to play one of the quad eight tracks in a normal stereo eight track player you would hear only half of the information for any given selection. The 1/4" open reel decks were the top end of consumer quadraphonic audiophile formats in the seventies. While not only having the best in discrete reproduction the decks could be used to make high quality recordings. owyheesound's first quality recording deck was an old four channel Teac 4033s deck. This deck was designed to be both a multi track recording deck and a quadraphonic tape player/recorder.
Recording quadraphonic is a good way to have something to play back in quadraphonic. Quadrophinic recording can be a very consumming hobby/profession as it requires special equipment that is often custom built and has double the demands than that of regular stereo recording. Generally all quad recording is done on a 4 discrete channel recorder. Some kind of pre-encoder could be used to record a 4 channel signal onto a stereo recorder but this would not alow for an kind of quality mixing or mastering.
Quadraphonic is an exciting way to listen to music and movies. owyheesound is endeavoring to create new music and film content for this audio format. Look for it here in the future.
owyheesound has a small collection of commercially released quadraphonic recordings that include titles from Santana to Pink Floyd. owyheesound also masters some original recordings which will be available for download in the future.
Here is a brief demo of a quadraphonic system: