Mono and Stereo Recording

All the operations so far described apply both to monophonic and stereophonic records. In the case of stereo, however, the magnetic tape used to record the original performance carries two separate channels of recorded information, and the recording head of the tape machine has two separate parts, one above the other. The signal from the left-hand side of the orchestra, through its main microphone and supplementaries, is reproduced from one channel of the tape.

The signal from the right-hand side, - through corresponding microphones, from the other tape channel. The transfer to the record of these two channels of sound calls for the cutting of a special stereo groove in the lacquer disc. This is, in effect, a double track, as opposed to the single track of a mono record. The stereo groove is a 90-degree V-cut, on one side of which is reproduced the signal from the left-hand side of the orchestra: on the other, the sound from the right-hand side. Both sides of this V-cut are independent, and give separate signals (though they are heard together).

Throughout the length of the record they maintain the same 90-degree angle to each other, but the depth of the V-cut varies constantly. Consequently, the stereo groove has both a lateral and a vertical component of movement-and the stereo stylus that tracks it must move, not only from side to side, but also up and down. (Most mono styli have only a lateral component of movement, and, if used to play a stereo record, will damage the groove).