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Speed variations on copied tape recordings.

Messages in this topic: 2 View All
badger danceDec 19, 2011

Hello Stephen,

You have hit the nail on the head where there has been multiple generational copies made of an original, it becomes difficult to isolate the original true reproduction speed.

If during a copy no variance is introduced you could isolate the phase shift of each 50Hz hum by amplitude to find which marker indicates the speed changes and so apply the correction. Knowing the tricks of the trade and what was got away with in the past I wonder if the copies were 'high-speed copies' were master and slave tape player/recorders were set up to duplicate tapes at double speed or if the copy was made 'down the line' using a frequency shifting process that moved interference out of band when decoded. In this case I assume that the discs were mastered in the UK and posted to Australia.

If the programme tape has a short burst of tone (900Hz) you stand a chance of looking at a wow & flutter figure for the tape and that might tell you something about the history of the tape. With first generation tapes you would tell the which particular tape roller introduced particular W&F errors. But I doubt that tone was included on the vinyl disc, but that said I would expect TRU to include a bit of tone on a recording shipped internationally.

One thing I would probably do if given the task would be to look at the waveform of the end of minute whistle and use that as my standard candle (to use the astronomical term) against which I could compare frequency and therefore speed variations during the programme.

Badger.

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