[DAVID B you are still sending messages with a Reply To only you 
header...hence the delay in this coming through. I had to resend.]

Lots of good comments in this thread.

I agree with all of them but offer this caveat. IF Tom Diamant meant 
that over time, all the tapes were recorded on different recorders BUT 
if he is pretty certain that each tape was recorded at the same time on 
the same recorder, then you can often recover the two tracks together.

The geometry is such that the azimuth error will be the same for both 
tracks (assuming your two-channel repro head doesn't have differential 
azimuth between tracks). Unless there are azimuth HF tones on both sides 
of the tapes, you'll be as close as you can get if the tape was recorded 
on the same machine in the same session.

Sometimes there will be a batch of multi-mono tapes (two or four track) 
that were all recorded at the same session and you're quite certain that 
only one machine was available for that convention or meeting or whatever.

But, I was going to say (and David Burnham beat me to it) you need to 
reverse azimuth of the reverse track IF THE FORWARD TRACK HAS ABSOLUTE 
POLARITY. If it does not, you might wish to reverse the forward track 



On 2015-03-09 3:49 PM, DAVID BURNHAM wrote:
> As was discussed in New Orleans in 2010, when you run both channels at the same time, (one forwards, one backwards), the one running backwards will have its phase or polarity reversed.
> db
>       On Monday, March 9, 2015 3:43 PM, Dave Radlauer <[log in to unmask]> wrote:
>   Hi Tom, long time.
> I've had no problem dubbing mono 1/2 or 1/4 track simultaneously.
> In my case from *J-corder* modified Technics 1520s.
> Dave Radlauer
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
Quality tape transfers -- even from hard-to-play tapes.