Different Sound Spectrum

GenXTechno Tags: stereophonic, quardraphonic, sound

Stereophonic Sound

Stereophonic sound, commonly called stereo, is the reproduction of sound using two or more independent audio channels through a symmetrical configuration of loudspeakers in such a way as to create the impression of sound heard from various directions, as in natural hearing. It is often contrasted with monophonic or "mono" sound, where audio is in the form of one channel, often centered in the sound field (analogous to a visual field).

Recording methods

X-Y technique: intensity stereophony

A-B technique: time-of-arrival stereophony

M/S technique: Mid/Side stereophony

Near-coincident technique: mixed stereophony

Quadraphonic sound

Quadraphonic sound consists of 4 channels, right front, left front, right rear, and left rear. Quad albums and equipment starting to show up in the early '70s, and as you can probably imagine, quad albums came in primarily 3 different formats, 8 track, record, and open reel, the first 2 being the most common. The stereo 8 track, like the name says, has 8 tracks, making 4 programs (4 programs * 2 channels = 8 tracks). The quad 8 track used the same number of tracks (again, like the name says), and has only 2 programs (2 programs * 4 channels = 8 tracks). One more difference to keep in mind (one of the many reasons quad didn't stay around) is that when the number of programs is cut in half, so is the time, meaning quad 8 tracks had to have more tape to get the same play time as their stereo counterparts.
The stereo record (like all records) has a 2 sided "V" shaped grove, in which the needle rides. The stereo (and quad) records have that groove cut at a 90 degree angle, so each side is 45 degrees to the surface of the record, and each of the 2 channels in recorded it's own side of the groove. Since it isn't possible to have a groove with more than two sides that will play back right or be compatible with existing equipment, quad records use encoding and decoding to take the 4 channels of sound and make them into 2 channels to store on the record, and to then separate the 4 channels back out when it's played. Either matrixing or modulation of rear channels onto high frequencies is used to make the original 4 channels fit onto 2 (There is more about this below).