Re: Recovering data from audio tapes

[Rubywand <rubywand@swbell.net>]

Metroplex wrote:
> 
> Hi,
> 
>     I am trying to help someone recover some very old data that
> was saved into audio tapes using an Apple II. Unfortunately, it is
> rather difficult to get hold of an Apple II around here. If you could
> help me with this task, I would greatly appreciate it. In particular,
> I have the following questions:-
> 
> 1. Do any of the Apple II emulators (for PC) support audio tape
> data format?

     The emus have a problem getting good 'old-apple' sound; so, it seems
unlikely; but, I do not know for sure.

 
> 2. Is there a simpler way? Special PC based tools to read and/or
> convert the data?

     Using some PC analog data analyzer is an interesting idea. But, having it
interpret the Apple II data sounds like more bother than writing a PC machine
code or assem tape input routine.

 
> 3. How robust was the tape format? (The tapes must be old so
> if the format is finicky, I may be SOL)

     Just tried loading a couple programs from our old tapes (from the early
1980's). One loaded okay and one didn't. (The one that didn't may require some
diddling with the output level.)  In similar checks in the recent past I have
not noticed that old tapes have been especially susceptible to going bad.

     One thing you do need to check is that the cassette's little felt pressure
pad has not slipped off. If it has, it can be glued back into place.

 
> 4. What was the format of the saved data? If I have the specs, I
> might be able to hack up something on the PC to read off the
> data and maybe even salvage damaged tapes.

     The whole business of cassette tape data recording going back to the mid
1970's is very strange. Designers seemed to have a fixation with converting
modem methods to tape and using complex circuits to make it work. Any programmer
who looks at the problem should immediately see that there is a much easier,
cheaper, and more reliable approach.

     Apple's method is the end-point of modem style approaches-- you detect
pulse length to identify 1's and 0's. On any decent portable cassette
recorder/player it is a moderately reliable technique which delivers a data rate
averaging around 1350 baud.

     Writing a routine to read Apple II tapes on a PC should be doable without a
lot of hassle. However, you would want to use a known-good tape for checking.
(My other-platform Apple II tape reader program was for a VIC-20-- handy for
transferring BASIC programs between the two computers.)  A good place to get
information is the disassem listings of the II/II+ monitor ROMS in the Apple II
Reference Manual (see pages 165 and 169).

 
>     I'd really appreciate any information pertaining to this as the guy
> I am trying to help is rather old and the data is one of this early
> thesis that he worked on. Thanks again in advance for any help!
> 

     If there is a local Apple II user, you could get the tape files moved to
diskette and, probably, get a printout of Text. Once the stuff is on diskette it
can be backed up, transferred to PC or Mac, uploaded to a BBS or net site, etc..
(By the way, files of Text for which you do not get a completely successful load
may still be largely recoverable.)

     An alternative is to make copies of the original using a good hi-fi tape
deck (at 'normal' copying speed).  These could be sent to Apple II users who
might like to help.



Rubywand