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From: TLC (all posts)
Date: 2001-04-24
Subject: Re: X1531 cable

Hi All!

Last week, there went a discussion about TAP files and the 'X1531 cable'.

IMHO using such stuff is both complicated and unreliable :-(. You don't just have to build another X1541-like interface cable, tap power from somewhere,
but also have to rely on the signal forming of the datassette. The only way to know if the file was loaded or not is to check it in emulator, then re-adjust head, try again, verify, readjust ... I think it's as bad as archiving tapes on the real machine. :-(

But nevertheless, archiving tapes is cool ;-). Me too, have some tapes that I've been always reluctant to archive by hand. When this discussion started and Lion has told us of SJPs 40 tapes I knew that I must do some steps ;-).

Well, to keep it short: I coded a small prog in Pascal that reads WAV files and does its best to pick up valid TAP streams from them.

This is nothing new, you could say, but there's something new in this routine:
it utilitizes tricks to obtain the real pulse width data. The signal goes through an AGC (automatic gain control), then an averaging LP filter,
derivating, AGC, filter, and _then tries to find valid pulses.

These stages make sure that even bad signals can be recognized. I did some tests. The routine was capable of presenting reliable TAP files from my worst tape - actually, a 'green' Polimer (Hungarians know what I'm talking about...)
that was also pretty much creased and I couldn't even load on the real 1351
:-O. Another test was to digitize the original (15+ years old) Exorcist game tape (Novaload of course...) using my WALKMAN (no head adjusting of course,
pretty blurred signal with lots of noise and glitches from the motor...),
still, the game from the TAP file loaded successfully in Yape ;-).

The program is a bit 'spartian' at the moment, no optimized code, no user interface, no error checking, no docs... but you can do some tests if you want; I can send the code / binary to anyone who wants. The stuff is in Free Pascal, so it can be compiled for both DOS/Winx + Linux easily.

I'd also need some info on the TAP file format. If anyone knows of good TAP file descriptions and things like that, please let me know, I'm sure I should know more about the format, to present a widely useable tool.

Best regards,

Levente