An Investigation into the Increase of Non-Linear Distortion Products from Virgin Tape to Disc Playback
A study was carried out in order to examine the increase in distortion products arising from the various stages in the recording process from virgin tape, via tape copies, right up to and including interaction with specific record pick-up distortions. 1 kHz sinusoidal signals as well as some IM (400 + 4000 Hz) and double tone (9800 + 10200 Hz) signals were recorded at levels increasing in discrete 3 dB steps starting in non-critical range and continuing up to tape compression level. The tape -original- and first and second generation copies were then transcribed together onto 12" LPs. This made possible a study of the distortion progression and also the second and third order distortion combination products. The current practice of recording right up to the modulation limits of the tapes as well as of the disc seems to result in a total distortion percentage which considerably degrades the sound quality. In order to gain an impression of the audible effect of these distortions, some special musical samples were recorded with the same discrete level steps as the measuring signals. These musical samples were subjected to the same copying and transcription processes as the measuring signals and were similar in character (single tone, multi tone). Listening to these musical sample records provided an opportunity to establish perceptibility limits for the human ear regarding amounts of disturbing distortion.
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