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I don't understand the virtue of playing the tape back on the same machine it was recorded on; any professional machine has separate record and pb electronics and heads so essentially they are two different machines anyway, except for the transports. 

db

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> On Feb 9, 2016, at 1:09 PM, Doug Pomeroy <[log in to unmask]> wrote:
> 
> 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
> [log in to unmask]
> 
> 
>> 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]