It's been many years since I have thought about this subject. Back in
1983 R-e/p magazine printed a letter I wrote in response to an article by
John Roberts about playing tapes backwards and the possible improvement
in transient response. Concerning the requirement that the tape be
played backwards, ideally on the same recorder which recorded it, this
means a second recorder was needed to capture the reversed audio and
that tape, when flipped, produced a phase-corrected tape running in the
normal direction (a digital processor could be used for the second reversal,
avoiding the losses connected with making an analog copy).
There is a letter in the Journal of the AES (1968, p 112, which I no longer
have) by J.W. Beauchamp which discusses this topic. He says "the Fourier
transform of a time-reversed signal is the complex conjugate of the signal
in forward time". I noted that British engineer Tony Faulkner reverse-records
his analog tapes, according to a news item in Studio Sound magazine in 1977,
which interestingly identifies this as being "an early American technique".
Doug Pomeroy
Audio Restoration and Mastering Services
193 Baltic St
Brooklyn, NY 11201-6173
(718) 855-2650
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On Feb 9, 2016, at 12:00 AM, ARSCLIST automatic digest system wrote:
> Date: Mon, 8 Feb 2016 21:23:34 -0000
> From: Ted Kendall <[log in to unmask]>
> Subject: Re: Playing reels backwards - separating myth from fact
>
> This runs counter to my own experience. Firstly, one great benefit of Dolby
> A was that straight copies of encoded tapes could be made without decoding,
> provided that the reference tones were retained on the copy, so there was no
> need to decode as part of the dubbing process. Secondly, to decode a Dolby A
> tape on reverse play is just plain wrong - the attack and decay
> chracteristics of the system are asymmetrical, so the decoding will be
> wrong, no matter how much you have finessed the other parameters.
>
Doug Pomeroy
Audio Restoration and Mastering Services
193 Baltic St
Brooklyn, NY 11201-6173
(718) 855-2650
[log in to unmask]
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