Audio and video recording technique

摘要

A method of producing recordings of an information signal which cannot be re-recorded on a tape recorder without unacceptable contamination by beat frequencies generated from signals recorded, together with the information signal, on the genuine recording. This is achieved by mixing, with the desired information signal, a number of signals above the audio frequency range which, upon playback, interfere with one another to produce beat frequencies in the vicinity of the bias frequency of a tape recorder. These beat frequencies interfere with the bias frequency and produce fresh subtractive beat frequencies which are in the audio frequency range. Apparatus for producing the contaminating signals comprises a set of oscillators (11, 111, 211) the output signals from which are combined via variable resistors at (17) and (31) to produce an output signal which contains not only the original oscillators signals but also beat frequencies at the sum and difference of all the oscillators. IMAGE