> On Feb 3, 2021, at 12:36 PM, Mattis Lind via cctalk <cctalk@classiccmp.org>
> wrote:
>
>> ...
>
> So you store a full track worth of data and then write it to the SD-card.
> Then move the flux-length data over to a PC and do post processing there,
> right?
>
> Isn't there performance in the CPU to do the actual decoding as well? FM,
> MFM, GCR or whatever into data. Find marks, check CRC and all that stuff?
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
