Timeline for Why can so little digital information be stored on a cassette tape?
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18 events
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| Oct 7, 2020 at 14:35 | comment | added | Fat32 | @PouriaP Ok... Don't forget to use zipping before storing digital bits... That will save you a lot of space on the limited resource you have... ;-) | |
| Oct 7, 2020 at 14:27 | comment | added | Pouria P | @Fat32 I was gonna use cassettes purely for the retro feel that they have. Thanks to your answers I now realize coming up with a new technique/modulation is more difficult than I thought. If I ended up doing it I will stick to available audio frequency shift keying techniques. | |
| Oct 6, 2020 at 22:47 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 6, 2020 at 22:15 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 6, 2020 at 22:11 | comment | added | Fat32 | @PouriaP The dial-up modem used about 3-4 kHz of transmission bandwidth that was allocated to commercial phone-line at that time. And reaching about 56 kbps indicates that the line had about 50-60 dB SNR (Signal to Noise Ratio). But it was using some advanced channel coding algorithms (together with Zip compression on the fly). I'm not sure if the scream you mention is a faithful representation of what's electrically passing through the line. If it's, then you can for sure use it. Why dont you use 2 layer DVD-Rs ? They are definetely high density, convenient and cheap? Why cassette? | |
| Oct 6, 2020 at 19:47 | comment | added | Pouria P | OK from all the technical jargon in the comments I'm starting to feel I'm in here way over my head. But your answer has given me new hope. Is it by any chance possible to convert my data into dial-up screams (that noise dial-up made) and record that in a tape? It's 56kbps so that's like 37MB in 90 minutes. Right? And I suppose it has built-in error checking and stuff in it as well. Not as interesting as writing my own modulation but from the looks of it I am utterly unfit for that task. | |
| Oct 6, 2020 at 11:56 | comment | added | Fat32 | @MSalters Yes it's an optimistic upper bound. I wish I knew the technical specs of the magnetic tape and read-write circuitry to provide a better answer. But I already mention the hiss noise, and frequency dependent SNR. Regarding the bandwidth, I guess it's somewhere between 10 to 16 kHz. Regarding the stereo; I didn't know tat cross-talk was so severe? But it can be undone. Remeber that once phone lines had dial-up modems but ADSL utilized unused bandwidth sitting idle in the copper. Or 4K re-scanning of (clean) optical films from 50's. So the capacity utilisation depends on technology | |
| Oct 6, 2020 at 9:08 | comment | added | MSalters | I'm pretty sure this answer is wildly optimistic about the capacity. Stereo on audio tape is not a fully distinct signal (stereo tracks are close together, but the signal is similar so interference is not that bad). SNR rapidly drops above 1 kHz; tricks like Dolby B are needed to make it sound acceptable. It definitely does not reach 20 kHz either. As a result, you can't multiply bandwidth by SNR. You must integrate SNR over the available bandwidth to get Shannon capacity. And to utilize this, you need ADSL-like subcarriers. | |
| Oct 5, 2020 at 19:57 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 5, 2020 at 18:04 | comment | added | Fat32 | @MarcusMüller Probably from this : It sounds certainly not as good as 90 dB, and it sounds certainly not as bad as 30 dB, therefore it should probably be 60 dB :-)) | |
| Oct 5, 2020 at 18:01 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 5, 2020 at 17:48 | comment | added | Marcus Müller | sadly, I don't; there's a couple of hifi forum posts that give the same numbers, but I'm not sure where they've got that from :) | |
| Oct 5, 2020 at 17:25 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 5, 2020 at 17:16 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 5, 2020 at 17:10 | comment | added | Fat32 | @MarcusMüller It comes from my ears at the moment ! :-)) (a comparison to CD music and casette music) I though the CD had 96 dB (16 bit assumption! though they are about 14 bits in reality) dynamic range then I assumed the cassette could provide 60 dB at most? I'm sure such data is available (at least Dolby Noise Reduction technologies makes use of them). If you know a better SNR estimate, please feel free to edit the numbers :-) | |
| Oct 5, 2020 at 17:08 | history | edited | Fat32 | CC BY-SA 4.0 |
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| Oct 5, 2020 at 17:07 | comment | added | Marcus Müller | nice one! by the way, where does the 64 dB SNR come from? That seems very high! | |
| Oct 5, 2020 at 17:04 | history | answered | Fat32 | CC BY-SA 4.0 |