Oh wow, I did not realize that floppy discs used the same exact encoding that was used on tape drives of the era, e.g. the TI-99/4A [1]. The wave file in the article is the exact same sound I'd listen to as a child, loading programs from cassettes. Total coincidence -- I recently have been recovering games from my old TI-99/4A cassettes, also using an oscilloscope (the same model in fact; for no particularly good rea…
> the same model in fact It could only be Rigol or Siglent. Fascinating though. I know how slow floppies are, but I wouldn't have imagined an oscilloscope to have the necessary resolution.
In my case, the data was coming from cassette tapes, so the oscilloscope was absolutely overkill in terms of raw bandwidth by 3 orders of magnitude. However I was operating at its memory limit of 14 MSa (megasamples)... running at a sampling rate of 20 kSa/s, I had barely enough memory to grab the full 10 minutes of each tape side.
Its vertical resolution (8 bits) I was a little worried about, but the dynamic range of Differential Manchester/FM is so low it turned out to be a nonissue. Certainly the quantization noise is comparable to the noise floor of the basic-quality cassettes that my data was on.
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