Audio tape interface revives microcassettes as storage medium • Hacker News Board

Re: Audio tape interface revives microcassettes as storage medium

#31

Post by hulitu » Sat, Oct 23, 2021, 5:58 AM UTC

adrianmonk wrote: post #27

femto wrote: post #21

Earlier quoted context omitted.

S/N for a cassette is variously given as 50dB, 58dB or 67dB [1,2]. Bandwidth is given as 12kHz (standard), 16kH (medium Fi), 19kHz (HiFi) for different quality cassette systems [3]. Let's simplify by assuming the frequency cutoff is a brick wall and the S/N is constant across the band. The maximum channel capacity for a cassette can be calculated using Shannon's Theorem [4]: C = B*log2(S/N+1) Cheap and cheerful (S/N=…

There's also stereo to consider, right? So you could get up to 2X bandwidth. (Channel separation issues might mean less than 2X in practice, though.) If you want to stretch the definition of "cassette", tapes are two-sided, and there were 4-track recorders that used all 4 tracks in one direction. They weren't anything too exotic. Musicians used them for cheap recordings for demos and such.

You don't want stereo. Only as an error correction maybe.

Re: Audio tape interface revives microcassettes as storage medium

#32

Post by brian-armstrong » Sat, Oct 23, 2021, 6:06 AM UTC

Out of curiosity I tried to do this using Quiet Modem, and the clocking was so much worse than I could have anticipated. I got a used deck from ebay that was in reasonably good condition. Listening to a tape on it, it didn't sound too bad, but when I did some analysis on a waveform on a tape, the playback speed was very uneven. Clock recovery is an absolute must with these, and in general I think it's worse than you'd imagine. Maybe if you had completely bulletproof internals could you actually make full use of the bandwidth.

Re: Audio tape interface revives microcassettes as storage medium

#33

Post by hellbannedguy » Sat, Oct 23, 2021, 7:26 AM UTC

LesserEvil665 wrote: post #4

I remember 6/7-year-old me begging my father for a tape deck to use with CoCo3. He refused, saying they were too expensive. Were they really in the early 90s? I doubt it. I lost interest in writing basic on that thing since I couldn't save programs. Anyway, I fully intend to try this out if only to close that loop.

This one was $269.00 at Circuit City.

It was the Cadillac of small tape recorders.

Most were under $50.

Re: Audio tape interface revives microcassettes as storage medium

#34

Post by eggy » Sat, Oct 23, 2021, 1:57 PM UTC

I had a normal size cassette player built into my Commodore PET 2001 back in 1977/78. Tape speeds are slow, but then again most of my programs were under 100 lines with some outliers at 250 to 350. Not a lot even for a cassette drive. Nostalgia of having to hit 'Play' button to load the program!

Re: Audio tape interface revives microcassettes as storage medium

#35

Post by adrianmonk » Sat, Oct 23, 2021, 4:53 PM UTC

hulitu wrote: post #31

adrianmonk wrote: post #27

Earlier quoted context omitted.

There's also stereo to consider, right? So you could get up to 2X bandwidth. (Channel separation issues might mean less than 2X in practice, though.) If you want to stretch the definition of "cassette", tapes are two-sided, and there were 4-track recorders that used all 4 tracks in one direction. They weren't anything too exotic. Musicians used them for cheap recordings for demos and such.

You don't want stereo. Only as an error correction maybe.

I'm not a tape expert, but in the spirit of learning more, I did some quick research, and it seems that multi-track tape is very common for data.

IBM started doing it in the 1950s and 1960s with 7-track[1] and then 9-track[2] tape. It's still being done today with LTO[3].

---

[1] https://en.wikipedia.org/wiki/IBM_7_track

[2] https://en.wikipedia.org/wiki/9_track_tape

[3] https://en.wikipedia.org/wiki/Linear_Tape-Open

Re: Audio tape interface revives microcassettes as storage medium

#36

Post by adrianmonk » Sat, Oct 23, 2021, 5:08 PM UTC

Const-me wrote: post #12

LeoPanthera wrote: post #6

Earlier quoted context omitted.

The sound quality of an audio cassette is at least as good, and almost certainly better, than the quality of an analogue telephone line. So I bet you could set a lower bound of at least 33.6kbit/s, since that was as fast as telephone modems went. 56k modems relied on your phone line being digital after the switchboard, but I would imagine that 56k should be doable as well.

Not sure it's directly comparable. When modem flips one bit, the CRC checksum in IP packet becomes incorrect, someone drops the IP packet, the condition is detected and the packet is re-transmitted. This slows down things substantially but user still gets their data. I think tapes need more reliability because there's only 1 try.

You could choose to do something similar with cassette.

It's common for tape drives to verify the data that was written. Rewinding is one way, but it's slow. A faster way is with two separate heads: as the tape moves, it passes over a write head first and then a read head.

You could maintain a buffer in RAM of data that has been written but not yet verified (as readable without errors). If you can verify it, you discard it from the buffer. If you can't, then you queue it up to be rewritten.

This wouldn't even require a special cassette deck. There were plenty of three-head audio cassette decks that allowed you to listen to the read head while making a recording. That made it much easier to set the right recording level.

(Basically, there were two common types of cassette deck: two-head and three-head. A two-head cassette deck has an erase head and a dual-purpose read/write head. A three-head deck has erase, read, and write heads. At least, that's the basic idea. Things get more complicated with auto-reverse cassette decks.)

Re: Audio tape interface revives microcassettes as storage medium

#37

Post by [deleted] » Sat, Oct 23, 2021, 10:10 PM UTC

rahimnathwani wrote: post #18

LesserEvil665 wrote: post #4

I remember 6/7-year-old me begging my father for a tape deck to use with CoCo3. He refused, saying they were too expensive. Were they really in the early 90s? I doubt it. I lost interest in writing basic on that thing since I couldn't save programs. Anyway, I fully intend to try this out if only to close that loop.

No one here can tell you whether your father was right or wrong. A tape deck and connection cable would have cost $35-$60 in the early 90s, which your father might have seen as closer to: A) A week's groceries for the whole family, or B) A single evening's entertainment for one person.

[deleted]