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From: ekijak@ARDEC.ARPA.UUCP
Newsgroups: comp.sys.atari.8bit
Subject: Re:  finding some use for 410 Program recorder
Message-ID: <8702091657.aa08801@ARDEC-3.ARDEC.ARPA>
Date: Mon, 9-Feb-87 16:57:49 EST
Article-I.D.: ARDEC-3.8702091657.aa08801
Posted: Mon Feb  9 16:57:49 1987
Date-Received: Wed, 11-Feb-87 05:09:23 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 15

The 410 records whatever you feed it just like a regular cassette recorder.
But when you try to play it back it passes the output from the tape head
(after amplification, of course) through two filters.  The output
of one filter is a dc voltage if a certain frequency is present, and zero or a
lower dc voltage otherwise; and the output of the other filter is a dc voltage
if a different frequency is present.  I don't recall the actual frequencies,
but they were something like 4 khz and 6 hkz, corresponding to the square wave
frequencies put out by the serial port when doing a csave or list "c:".  The
two outputs were combined in a comparator (If I remember correctly) and the
final output was a high or low TTL signal.  This is what got sent back into the
serial port when you loaded the saved program back in.  If you grab the signal
before it goes into the filters, you may be able to recover the original audio.
Also, one of the tracks IS an audio track in that on playback, it gets sent
directly to the monitor (TV) speaker.  I don't know what (if anything) it does
on recording (csave'ing).