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Hi, Tom,

This is something I would love to hear Jay McKnight's answer to, but I 
think Ted and John Chester succinctly nailed it. The below was mostly 
written prior to seeing the other two great replies.

The first comment: you will also need to reverse the absolute polarity 
of all tracks. I had this confirmed when I did a two-track 
letter-from-Vietnam tape recently. I did it in one pass (nice thing is 
that the azimuth alignment works the same for both sides if they were 
recorded with the same azimuth). The system had a very asymmetrical 
voice waveform and it was VERY obvious that the two sides were in 
opposite polarity.

As to better, it's hard to say. Why don't you take a good tape and try 
it? See what you think. Of course, to remove absolute polarity bias, you 
will need to invert the polarity on the reverse-play copy (assuming the 
forward play polarity is correct). If you like the reverse play 
uncorrected better, then flip the polarity of the forward play version.

The best thing would be to sort-of align all 8 tracks in the DAW and 
then gang the two sets so you can solo one set quickly to do rapid 
switching A-B comparisons as well as long-form listening.

There are two thoughts about this:

(1) since analog filters have group delay, running it backwards 
compensates for that to some extent

(2) since analog filters have group delay and it's expected, running it 
backwards messes things up compared to how we are used to hearing tapes 
sound

An interesting thought was what Studer published about their new attempt 
at tape equalization and phase compensation. This throws another 
variable into the equation. I always wondered how this affected 
interchange with machines that weren't configured this way. This was 
initially published upon the introduction of the A810. Since the A820 
uses many of the same electronics cards, one might think that this is 
also applicable to the A820. I am not certain. Goran? I suggest reading 
the papers, however. I have them on my server, but I just checked and 
they are still on the Studer ftp server.

ftp://ftp.studer.ch/Public/Products/Recording_Analog/A810/Technical_Info/PI_1982-01_E_A810_New_Developments.pdf

and

ftp://ftp.studer.ch/Public/Products/Recording_Analog/A810/Technical_Info/SwissSound_A810_Phase_Compensation.pdf

If you would prefer to click on the individual files, point your browser to:

ftp://ftp.studer.ch/Public/Products/Recording_Analog/A810/Technical_Info

SwissSound_A810_Phase_Compensation.pdf
PI_1982-01_E_A810_New_Developments.pdf

As the two other responses said, there are other networks in addition to 
the R/P "standard" EQ, including the head itself. Based on my experience 
in doing this, whatever the difference is, it is small. I find that 
often absolute polarity is a bigger difference than direction of 
playback. But, I generally do reverse playback on voice grade tapes and 
most of the voice grade tapes I get are poorly recorded but they have 
Grandma's voice on them.

As an aside on this entire process, be careful in transferring 
quarter-track stereo as inline heads have measurably poorer crosstalk 
performance than the normal quarter-track stereo heads.

I had originally thought to modify an A80 with four playback electronics 
channels--it's not THAT hard and I have a spare bucket, but when I 
thought about the crosstalk, I simply mounted a quarter-track stereo 
head and for those quarter-track stereo tapes I choose to do on the A80, 
I do each side in a separate pass.

Cheers,

Richard


On 2/7/2016 8:48 AM, Tom Fine wrote:
> Hi All:
>
> I am about to transfer a small pile of Quad reel tapes, and wanted to
> revisit this question -- which also applies to full-track and 2-track
> tapes -- will I get better results playing the tapes tails-to-heads (in
> reverse) and then reversing the digital file (back-to-front), and of
> course assigning the correct tracks to the correct channels (the tape
> would be upside-down if played backwards, so 1=4, 2=3, 3=2 and 4=1). I
> have read commentary that playing a reel backwards allows for sharper
> wave fronts and thus crisper dynamics. It seems like it wouldn't _hurt_
> anything to play the tapes backwards, but I would like more info from
> the tape-playback experts.
>
> Important to note - I know this can't be done with NR-encoded tapes,
> that those must be played forward (the regular way) for the NR decoder
> to work properly. But what about if I transferred the tape backward and
> then send the digital audio out to the decoder, is there any reason that
> would work? (I don't think so, but wanted to ask the experts).
>
> Thanks in advance for facts/discussion about this topic.
>
> -- Tom Fine
-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.