Weird question: audio cassettes

[Fallingwater]

I remember when the Commodore 64 could fit about a megabyte of data per side on a 30-minute cassette. Thinking about this got me wondering: using modern data compression and translation methods, would it not be possible to store significantly more data on normal audio cassettes?

This would be completely useless from a practical point of view, as cassettes are surely incapable of holding multiple gigabytes (I'd guess maybe 30-50 megabytes?), but it might have some use for hiding stuff. Say you have small amounts of secret data you want to backup (text, or spreadsheets); put them on a passworded rar file, and record that on a cassette. Put the cassette in a box with other audio cassettes with actual music on them, and nobody would ever think of looking in there for your SUPAH SIKRIT stuff when there's hard drives and CDs all over the place.

 

[Mark R]

1 MB per side - not using the conventional OS tape control system. You could get about 32 kB on a 15 minute side. The tape recorded at 300 bps, if I remember correctly, using frequency shift keying between 1200 and 2400 Hz.

There were a number of 'turbo tape' software packages, that would record the data at approximately 4-6x the data rate. I'm not sure what they actually did to achieve that though.

One of the problems for the C64 was that it had a digital input from the tape - a 'negative voltage' would be a 0, and a 'positive voltage' would be a 1. This would allow the software to detect the frequency of the sound on the tape, and made it generally quite resistant to noise.

Modern signal processing techniques would be much better able to utilize the capability of the tape. Good quality tape and equipment had a frequency response of about 20 kHz, and SNR of about 60 dB, which is as good as vinyl and approaching CD fidelity. (But such quality tape was rarely used, except as master tapes for radio stations, small bands, etc. - I once snagged a whole box of top quality audio tapes which were being chucked by a radio station, which had used them as the masters for their jingles- you could tell they were quality, because instead of being made of plastic, the actual shell was made of magnesium alloy)

So, with a reasonable allowance for error correction, SNR margin, advanced modulation techniques, etc. I'd expect you should be able to get about 10-20 kB/s (or about 2-4x the rate you'd get via a 56 k modem) - depending on the quality of the deck and tapes.

Video cassettes are much more practical - they hold huge amounts more data. There were a number of commercial products available that would allow you to connect a VCR and use it as a tape drive for backup purposes. They used to work at a better data rate - I seem to recall they would get several GB on a 3 hour tape, giving a data rate of around 300-500 kB/s.

 

[Rubycon]

1 MB per side - not using the conventional OS tape control system. You could get about 32 kB on a 15 minute side. The tape recorded at 300 bps, if I remember correctly, using frequency shift keying between 1200 and 2400 Hz.

There were a number of 'turbo tape' software packages, that would record the data at approximately 4-6x the data rate. I'm not sure what they actually did to achieve that though.

One of the problems for the C64 was that it had a digital input from the tape - a 'negative voltage' would be a 0, and a 'positive voltage' would be a 1. This would allow the software to detect the frequency of the sound on the tape, and made it generally quite resistant to noise.

Modern signal processing techniques would be much better able to utilize the capability of the tape. Good quality tape and equipment had a frequency response of about 20 kHz, and SNR of about 60 dB, which is as good as vinyl and approaching CD fidelity. (But such quality tape was rarely used, except as master tapes for radio stations, small bands, etc. - I once snagged a whole box of top quality audio tapes which were being chucked by a radio station, which had used them as the masters for their jingles- you could tell they were quality, because instead of being made of plastic, the actual shell was made of magnesium alloy)

So, with a reasonable allowance for error correction, SNR margin, advanced modulation techniques, etc. I'd expect you should be able to get about 10-20 kB/s (or about 2-4x the rate you'd get via a 56 k modem) - depending on the quality of the deck and tapes.

Video cassettes are much more practical - they hold huge amounts more data. There were a number of commercial products available that would allow you to connect a VCR and use it as a tape drive for backup purposes. They used to work at a better data rate - I seem to recall they would get several GB on a 3 hour tape, giving a data rate of around 300-500 kB/s.

Cassette tape really struggles to get to 20kHz and degrades too fast.
VCR tech with its helical scanning technology has much higher bandwidth.

 

[Fallingwater]

1 MB per side - not using the conventional OS tape control system.

That's right. According to Wikipedia, 1MB was only achievable through the use of the turbo-loaders you mention - but it was still achievable.

So, with a reasonable allowance for error correction, SNR margin, advanced modulation techniques, etc. I'd expect you should be able to get about 10-20 kB/s (or about 2-4x the rate you'd get via a 56 k modem) - depending on the quality of the deck and tapes.

Interesting. This would achieve approximately 36 to 72 megabytes per hour of cassette tape. On a C120 two-hour cassette, this would actually offer some fairly decent backup capabilities. Or it'd be just fun to try for kicks and giggles.
How would I go to accomplish this? I imagine I'd have to connect a deck to the sound card and record/play from that, but what do I use to convert the data to sound?

Video cassettes are much more practical - they hold huge amounts more data. There were a number of commercial products available that would allow you to connect a VCR and use it as a tape drive for backup purposes. They used to work at a better data rate - I seem to recall they would get several GB on a 3 hour tape, giving a data rate of around 300-500 kB/s.

Seriously? This sounds awesome. As long as one had the patience to wait for the backups to complete, it'd offer capacities actually useable today. How come such products didn't take the tape-drive market by storm?
Any more data on these systems would be very appreciated - I'd very much like to grab one on eBay or something, provided they haven't become collectibles worth a lot more money than I'm willing to invest in what is essentially a "because I can" thing.

 

[alaricljs]

My mini-DV camcorder with firewire connection can be used to store data at about 12GB/tape uncompressed. No different than the cassette idea in terms of being "discoverable" but able to store way more data.

 

[bamacre]

Or you could just burn the data on a DVD you labeled "Rocky V."

 

[magreen]

Or you could just burn the data on a DVD you labeled "Rocky V."

Better yet, label it Titanic. Any guy will stay the hell away from it! :biggrin:

 

[sxr7171]

Sounds like a TDK MA-XG. Sony had one with a ceramic shell. Tapes of that caliber were designed for "metal" biasing. Anyway, while most tapes struggle to hit 20KHz and in reality even 14KHz, these tapes with the right Nakamichi deck could exceed 20KHz frequency response. The cost of achieving that performance was very high then and would be now. The MA-XG was $19 a tape for example.

Anyway getting to the point I'm sure that today you could devise a way to hold a decent amount of data on one. More than a few spreadsheets worth. I suspect maybe 200MB. There are 4 tracks on a cassette.

In any case as an audiophile format, it wasn't. Some people used it with high end equipment for personal recordings, but they are highly equipment sensitive, best played on the exact same deck they were recorded on. It was the worst format to buy music on.