Changing Tracks On An Eight-track Tape

An eight-track tape stored an album as four two-channel (i.e. stereo) programs or (rarely) two four-channel (called quadaraphonic or quadrasonic at the time; would be called “4.0 surround” today), storing one channel from each program on on of its eight tracks. Each of the four or two programs can be logically thought of as equivalent to the “side” of a vinyl record or a cassette tape. (If you have only ever handled CDs? or MP3s?, then I am not sure how to explain this to you).

The tape deck would switch programs by sliding the head assembly by the width of a track. On a stereo tape, program 1 would use tracks 1 and 5; program 2 would use tracks 2 and 6; program 3 would use tracks 3 and 7 and program 4 would use tracks 4 and 8. Similarly, on a 4-channel tape, program 1 would use the odd tracks and program 2 would use the even tracks.

On a 2-channel player, the head movement was the whole program changing mechanism. On a 4-channel player, since they could play stereo tapes also, an additional electronic mechanism would enable two of the four tape heads to be selected, as well as sliding the head assembly from side to side.

Regardless of mechanism, however, the task of changing the program is very simple. A pushbutton on the front of the tape deck, usually accompanied by a set of lights or an indicator of some sort was the interface. The lights or indicator would tell you which program was currently playing, and pressing the button would advance this by one. If you were listening to program 4 on a stereo tape, pressing the button would move to program 1. If you were listening to a quadraphonic tape, pressing the button switches to the “other” program (as there are only two).

For what it's worth, the format came about as an extension of tape cartridges (Carts) used in Radio and Television broadcasting. Those tapes were only three tracks (two for program audio and one for cue tones for 'idiot lights', end of tape and automation purposes) and turned at a reel-to-reel speed of 7.5 ips yeilding very good sound quality. They were used primarily for commercials, but some stations actually put all thier music on them, saving precious vinyl.

There were numerous reasons why the eight-track format yielded to cassette tapes. One was that most eight-track players made a loud “ka-chunk” sound as they changed tracks. Most vinyl records were about 20 minutes long on each side, and so each of the four programs on an eight-track tape reproduced half of one side of an album - meaning a “ka-chunk” occurred about every ten minutes. Sometimes manufacturers changed the song order to fit them most efficiently on each of the four programs, so that a listener felt that the tape didn't reflect the recording artist's intentions. Cassette tapes were much smaller, and duplicated the vinyl record experience in containing 20-30 minutes of music on each side. Turning the tape over was not considered to be an inconvenience, since users were accustomed to doing this with vinyl records.