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implies, the erase head removes from the tape any earlier recordings before they reach the record/playback head. Obviously, you do not want the erase head to be operative when you are playing back the tape and it is therefore arranged to work only during recording.
There are two ways in which the magnetic recordings can be erased. The simpler consists of passing the tape over a small permanent magnet. In effect, this magnetises the whole tape uniformly to the maximum extent. The playback head responds only to variations in the degree of magnetisation of the tape and so reproduces no sound from a uniformly magnetised tape. In practice, however, small variations in the uniformity of the tape will produce spurious impulses in the playback head. These may be audible on playback as a hissing sound.
For this reason, the majority of recorders use another kind of erasure. This is effected by an erase head which is very similar to the record/playback head, but has a much wider gap. The erase head receives no recording impulses: only a high frequency current similar to, but stronger than, the supersonic bias. The stronger agitation so produced acts
A typical domestic tape recorder. Tape leaving the feed reel passes the erase head and then the record/playback head. The tape is drawn past the heads at a constant speed by the capstan against which it is held by a pinch roller. Recordings can be made either from a microphone or direct from a radio or gramophone pick-up.
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