Subject: RE: Preserving ancient media

From: "Hills, Paul" <[email-masked]>
Date: Mon May 19 10:12:10 2003

That's sort of what I was thinking of. Of course, as you say, it is ZX81
specific.

Were these home computer tape format's standardised in any way, or at least
based on an older standard? I seem to remember a format called
"Cottis-Blandford" from years ago. Am I right in saying that most home
computer's tape data format was 1200Hz and 2400Hz for logic 0 and 1 (maybe
the other way round). How many stop/start & parity bits (and possibly more
control bits) are sent may be computer-specific I guess.

Sampling the audio stream and decoding the 0s and 1s would not be too hard a
task if a sound card with easy access to the sampling hardware was
available. It would then be relatively simple to write an application would
allow the number of start, stop, data (probably 8!) and parity bits to be
selected, world decode the string of 0s and 1s into a byte-file. The format
of this file, again, would be computer-specific of course.

If I get time I may have a go at this.

paul

-----Original Message-----
From: David Holland [mailto:[email-masked]]
Sent: 17 May 2003 02:36
To: Classic Computer Talk
Subject: RE: Preserving ancient media

The following MIGHT be a good place to start:

http://www.geocities.com/SiliconValley/Ridge/9965/

ZXTAPE 3.0   Its directed towards the zx81, but it could 
be applicable to your application.    Dunno. I've a feeling every
computers tape format is different, though.

David

On Tue, 2003-05-13 at 03:25, Hills, Paul wrote:
> I have quite a bit of software on cassette tapes for 1980s home computers.
> Does anyone know of a simple method (without having to design and build
> myself a dual-tone decoder circuit + write suitable PC software) of
getting
> this information onto a PC? I guess the home computer emulator pages on
the
> web must have done this.
> 
> Maybe I could record it as a WAV file then write a program to decode the
> WAV? Or would MP3 encoding be capable of compressing and reliable
expanding
> the audio data (MP3 is of course designed to compress music which these
> squeaks and whistles clearly are not, even if they lie within the audio
> spectrum!).
> 
> paul

---

From: [email-masked] (Tony Duell)
Date: Wed May 21 10:05:13 2003

> Were these home computer tape format's standardised in any way, or at least

Not at _all_ Just about every manufacturer did it his own way...

> "Cottis-Blandford" from years ago. Am I right in saying that most home

I thought the common one was 'Kansas City', but that was not common on UK 
home computers (the BBC micro was perhaps the closest to it).

> computer's tape data format was 1200Hz and 2400Hz for logic 0 and 1 (maybe

No! Some did, many didn't.

What's worse is that some manufacturers used a constant time for each bit 
(so that one state was a single cycle of 1200 Hz, the other was 2 cycles 
of 2400 Hz, say), but many other manufacturers used a single cycle at 
each frequency for the 2 states. This means the bit rate is not even 
constant...

> control bits) are sent may be computer-specific I guess.

However, a reasonable quality digital audio recording of these old tapes 
might well be enough to preserver them (you could play it back to a real 
tape, or directly into the home computer). It's not an efficient way to 
store the data, but it's better than losing it totally.

-tony