Stereophonic Source Material

Author: N.H. Crowhurst

Different sources for stereo program

To get the most from a home form of entertainment such as stereo, we need a variety of sources. The first - because it was the easiest to adapt - was the two-channel tape recorder. An early attempt to apply it to discs used two separate grooves, spaced apart by a fixed distance. But this was very clumsy to use. What was needed was a means of putting two channels into one groove. This is not basically difficult, but it has practical difficulties that are not really audio problems.

The first idea was to use up-and-down motion of the stylus for one channel and the regular sideways motion for the other. As both are mutually at right angles, neither should affect the other, and they can carry essentially independent programs. With this method, the quality of the two channels was not equal. To overcome this, two motions mutually at right angles are used, but each is at 45° to either vertical or horizontal. This enables equal quality to be used in both channels. By phasing the channels so that unison between them results in the vertical components canceling and the horizontal components adding, the new 45/45 records are compatible with the unstereo-phonic LPVthat only carry sideways-motion grooves.

For radio there are several possibilities: an AM broadcasting station can carry one with the FM station carrying the other; two FM stations in the same area can work together to send out half each of the same program. Various other combinations between TV and either AM or FM have been used. But the most promising for general use is one of several multiplexing methods (two channels on a single FM channel) that an adapter can "decode" at the receiver.

Two channels in a single groove