mattislind at gmail.com
Wed Feb 3 12:17:18 CST 2021
Den ons 3 feb. 2021 kl 18:55 skrev Al Kossow via cctalk <
cctalk at classiccmp.org>:
> On 2/3/21 9:43 AM, Paul Koning via cctalk wrote:
> > A nice benefit of capturing the raw waveforms and post-processing them
> is that you can do all sorts of very complex processing. If the media are
> nice and clean then simple processing is sufficient. If they are badly
> damaged, you may need more. If you do the processing in real time you may
> not know what all is needed. But if you do post-processing, you can add to
> the algorithms after data capture has been done, if what you have so far
> isn't yet good enough.
> > I can imagine techniques like digital filtering, adaptive filters,
> maximum likelihood decoders, etc.
> > In recovering data from tapes, with multiple tracks, people have often
> done this same sort of thing, full high bandwidth analog signal capture.
> You don't even need to know at the time what the data format is. If you
> think you know but you don't have it quite right, no matter, you just
> change the software and run another pass through the captured waveforms.
> No need to run the (possibly fragile) media through the machine again.
> > paul
> In the real world, this is fundamentally wrong.
> You need to know you haven't captured garbage while the disk is still in
> the drive
> and you want to minimize the time you spend dwelling on an individual
> Magtape is a completely different issue where you attempt to get as much
> information as you can
> before the tape sticks, tears off all of its oxide, or the head clogs.
> Even if it doesn't stall, the motor can drag and goofs up the tape speed.
> This is an issue
> for NRZI media.
> We (CHM) have had amazing luck recovering 50+ year old 7, 9 and Whirlwind
> tapes with analog
> recovery. See Len Shustek's talk at VCFW 2001 about the recovery software.
> There is some hardware work going on to recover double-sided floppies
> using A/D channels
> digitizing both sides of the disk simultainiously, and recovering 4-track
> pre-QIC cartridge
> tapes the same way.
I have been looking into designing a 12 bit A/D with a differential
amplifier in front which would sample at 6, 12 or 24 Mhz delivering the raw
samples to the host over USB (FX2LP chips are good at pumping USB data). In
this way I have all the info I can get and then applying various algorithms
to the signal is the task of the host. If the host is quick it might even
be able to do processing in real-time? (
https://github.com/MattisLind/AnalogFluxReader) Need to work on the layout
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