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Comment by jacquesm | Hacker News Reader

What kind of physical format do those tapes have?

They are half-inch wide 7-track tapes. It's the 7-track bit that makes them difficult to read (I have a half-inch machine but it's 8-track). I think it was NASA and a few other government agencies using this 7-track format (or 1-inch 14-track), rather than the 1/2-inch 8-track / 1-inch 16-track used in audio studios.

The workflow for these tapes is described on the Chilton Computing website [1].

(Note: this is analogue 7-track, not to be confused with the digital 7-track format used by early IBM mainframe machines).

[1] http://www.chilton-computing.org.uk/acl/applications/satelli...

There is a Teac 1/2 " that does 8 tracks, you could probably read them one track at the time by judiciously jiggling the height of the head relative to the base of the player. The heads are narrower than a single track so that should work. The analog format is likely simple FSK or some variation on that theme.

It would take 7 passes to get it off assuming only one of the heads lines up with a track at any given time. Keeping the sync between the tracks will be the hard part. I'm in Europe so that probably rules out collaboration on this but if there is some way to get me a sample of such a tape I'll be more than happy to give it a shot.

edit: this machine: https://soniccircus.com/product/teac-80-8-1-2-8-track-analog...

The machine I have is very similar to that (Tascam 38), although the Teac 80-8 has the advantage of being able to run at the correct speed (7.5ips while the Tascam 38 only runs at 15ips).

From reading the papers published at the time (mid-to-late 60s), it seems the encoding scheme was based off a comb-filter, although I don't honestly understand enough to actually describe how it works.

I've had the tapes for around 5 years now, and managed to do basically nothing. It would be good to finally make some progress! I'll send you an email.

The speed isn't that much of a problem, it can be fixed after the signal on the tape is digitized.

Looking forward to your email, I love these kind of projects.

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