> On Aug 4, 2026, at 1:51 PM, David Gesswein via cctalk <[email protected]>
> wrote:
>
> On Mon, Aug 03, 2026 at 10:59:12AM -0700, Len Shustek wrote:
>> At Sat, 1 Aug 2026 20:42:23 -0400, David Gesswein <[email protected]>
>> wrote:
>>> 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.
>>
>
> 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.
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
