4 ms·

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

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.

p1mrx 5y ago
I wouldn't automatically assume that tape is better than a phone line. For instance, a phone line will always clock at 1 second per second, because everything runs in real time with no storage.
- LeoPanthera 5y ago
  I can’t imagine that clock recovery would make a huge amount of difference.
- TedDoesntTalk 5y ago
  Analog phone lines were limited to 4 KHz frequency range in the US. Compare that to tapes close to 20 KHz.
Const-me 5y ago
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.
- LeoPanthera 5y ago
  I remember back in the 80s when my BBC Micro would miss a bit it would just beep and tell you to "Rewind tape", which meant, go back about 10 seconds. And then it would figure it out from there.
- tenebrisalietum 5y ago
  The Commodore 64 (and possibly earlier Commodore systems such as the PET and VIC20) actually recorded each "block" twice on the tape, and could correct up to 31 errors per block as long as an error didn't affect the same exact byte in each block (it didn't do anything like ECC). This also made loading/saving from tape really slow - 50bps.
  - krallja 5y ago
    SiriusXM uses a similar method, plus buffering, to ensure your satellite radio keeps playing, even if you dare to drive under such rare things as traffic lights and tree branches.
- adrianmonk 5y ago
  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.)

p1mrx 5y ago

I wouldn't automatically assume that tape is better than a phone line. For instance, a phone line will always clock at 1 second per second, because everything runs in real time with no storage.

LeoPanthera 5y ago
I can’t imagine that clock recovery would make a huge amount of difference.
TedDoesntTalk 5y ago
Analog phone lines were limited to 4 KHz frequency range in the US. Compare that to tapes close to 20 KHz.

Const-me 5y ago

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.

LeoPanthera 5y ago
I remember back in the 80s when my BBC Micro would miss a bit it would just beep and tell you to "Rewind tape", which meant, go back about 10 seconds. And then it would figure it out from there.
tenebrisalietum 5y ago
The Commodore 64 (and possibly earlier Commodore systems such as the PET and VIC20) actually recorded each "block" twice on the tape, and could correct up to 31 errors per block as long as an error didn't affect the same exact byte in each block (it didn't do anything like ECC). This also made loading/saving from tape really slow - 50bps.
- krallja 5y ago
  SiriusXM uses a similar method, plus buffering, to ensure your satellite radio keeps playing, even if you dare to drive under such rare things as traffic lights and tree branches.
adrianmonk 5y ago
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.)