4 Aug
2026
4 Aug
'26
9:58 a.m.
On Aug 4, 2026, at 1:51 PM, David Gesswein via cctalk
<cctalk(a)classiccmp.org> wrote:
On Mon, Aug 03, 2026 at 10:59:12AM -0700, Len Shustek wrote:
Dealing with analog stuff can be a mind-bender for us digitally oriented folks. Reading a
good book about DSP can be a big help. Lots of good things can be done with filtering,
and FIR filters are very powerful and flexible. One book I've used a lot and would
recommend as a starting point is by Marvin Frerking, Digital Signal Processing in
Communications Systems. As the title indicates, its oriented to readers who do radio
receivers and transmitters, but all the common basics are there that would apply to any
place you would consider DSP.
paul
At Sat, 1 Aug 2026 20:42:23 -0400, David Gesswein
<djg(a)pdp8online.com> wrote:
I looked at your code at the start. DECtapes aren't anything like 9 track.
They are closest to wirlwind so thought about trying to modify that. Ended up
adding the analog to digital decoding to my existing digital decode code vs
learning a new code base and modifying it. Was harder getting good bits from
the analog data than I thought so may not have been the best choice. The code
works pretty well now. The reader is a bunch of instrument amps that
amplify to levels usable by
Saleae logic 16 pro which has analog digitization mode and way too many
times repurposed code to decode it. Doesn't look like I have put it online
probably because the code is embarrassing but ok with giving it away if
someone has use for it.
Here's an alternative to consider: Years ago I wrote a program to decode
waveforms digitized from cruddy old mag tapes in various formats,
including 7-track NRZI, 9-track NRZI, PE, and GCR, and 6-track Whirlwind.
https://github.com/LenShustek/readtape
We've read hundreds of tapes, mostly digitized using a Saleae analyzer.
I never wrote a DECtape decoder, but it would be doable.