I agree that I probably don't get full response out to 40 kHz from the
repro electronics, but I do recall having flat R/P response on an A810
to about 29 kHz at 7.5 in/s at 250 nWb/m--more at -10. The APR was, I
think, in the same ballpark. I was surprised.
Since I can get close to flat response at 1.88 in/s out to 8 kHz on the
APR using the MRL tape, then, since gap loss is a wavelength response
issue, that translates into a gap loss cliff at 32 kHz at 7.5 in/s and 2
kHz at 15/32. Perhaps I was overly optimistic saying 2500 Hz, but
certainly 2000 Hz is doable. My clients have been happy with the logging
tapes done this way.
Most logging tapes are horrid quality to begin with. When using the
official reproducers back in the day, I got results that were worse (in
my memory) than what I got recently using some sort of convoluted setup.
So, I respectfully disagree with only a few hundred Hz bandwidth for the
entire system at 15/32--my guess is probably at least 1.5 kHz, but I'd
bet usable to 2 KHz or above.
On 2012-04-13 6:56 PM, Goran Finnberg wrote:
> Richard Hess:
>> I've found 96/24 at 7.5 in/s is adequate for 15/32 logging tapes.
>> If you start with 40 kHz bandwidth and take that down 16 X you
>> end up with 2500 Hz bandwidth which is probably optimistic for
>> most 15/32 logging tapes. Comms channels are brick walled at
>> 3000 or 3200 Hz.
> Yes, you have 40 kHz bandwidth from the A/D conversion ONLY.
> What will the gap losses do when replaying 15/32" tapes ?
> And since I like to use a flux loop to understand what happens above 20 kHz
> electrically in the playback electronics I can tell you that almost every
> tape machine I have looked at they intentionally drop off very fast above 20
> The intent here is to avoid having the erase/bias frequency getting out of
> the machine.
> Even the Ampex ATR 102, when the input damping potentiometer in the replay
> amplifier is correctly set as per the manual, rolls off swiftly above 20 kHz
> Unless you have replay heads having very narrow gaps with gap loss
> correction and replay electronics designed for greater than 60 kHz response
> and the replay head has sufficiently low inductance AND very low capacitive
> loading you just will not have 40 kHz all the way from tape to A/D input.
> Thus you may have in practice nothing better than a few hundred Hz in actual
> bandwidth due to restrictions before the A/D when you replay 15/32 tapes at
> 7.5" speed.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Quality tape transfers -- even from hard-to-play tapes.