Re: RAM Applesoft found!

[Andy McFadden <fadden@fadden.com>]

Michael J. Mahon <mjmahon@aol.com> wrote:
>> Maybe. It's good enough for music tapes though. And I noticed that the 
>> Apple tape played much less loud than the new copy I produced with the 
>> Commodore Datasette in an early attempt to get this working. Do tapes 
>> get softer over time as the magnetization averages itself out maybe? Or 
>> maybe Apple tapes are just by nature less loud than Commodore tapes.
[...]
> The alignment doesn't have to be off by much to degrade the high
> frequency response enough to bother the Apple read routine.  I have
> also encountered "professionally" duplicated cassettes that were
> recorded with bad alignment--I had to misalign a deck to recover
> the data from that one!

You can see some screen shots of a WAV file on http://www.fadden.com/fft/
from a piece of an Apple II tape.  The page is actually about a buggy
FFT filter implementation, but it shows the sort of distortion that
accumulates over time.  The Apple II relies on zero crossings, and in
some cases low-frequency noise pushes the signal completely above or
below zero.

I don't actually know *where* the noise comes from.  It could be
related to my decidedly non-studio-grade equipment, but it doesn't show
up on all tapes.

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