Recent Finds & Thoughts

From: Allison J Parent <allisonp_at_world.std.com>
Date: Fri Nov 27 14:38:46 1998

< ::How did that work? Made the S/N ratio horrible on copies? AFAIK no
< ::cassette recorder, at least not of the cheap consumer type, ever had
< ::automatic level control on _playback_.
<
< That was the idea, yes.

All that would do is make a high precentage of poorly readable tapes.
Likely they load their own loader that used a modified format that was
not the same. Lowering the level on audio casette where you only have
at best 34db (non dolby) of headroom on a portable would make a very
crummy recording. Dubbing through a level controlled amp would beat
that in a heart beat. The trick is imposing low freq noise like hum
or other tones below 40hz that are unheard at normal play speeds as they
are under the ability of the head to resolve. When you dupe tape at high
speed 5x-10x the then say 20hz tone is now a resolvable 100-200hz and
gets embedded (summed with data) as interfering noise (like a bad AC hum).

< ::> days before automatic level control), or required odd azimuth settin
< ::> would be toasted by dubbing. This probably shouldn't interfere with
< ::
< ::All that having the wrong azimuth would do is reduce the HF response.
< ::There's no way to tell an original played back on a machine with the
< ::heads at a different azimuth setting to the recording machine and a co
< ::of that recorded and played back on the same tape deck AFAIK. No casse
< ::recorder had software-controllable azimuth.

This is all bogus. Recording with the azimuth off kills the HF response
and no amount of tweeking with recover that on playback. It's not on the
tape so there is nothing you can recover. The wider the head gap or track
width the worse it will be. Casette recorders were full track mono (half
the width of the tape) so they were wide! If it's wrong on playback same
thing save for it's correctable.

Back in the audio cassette days I've seen more attributed and fixes
created based on presumed behavour. Every thing from amps to filters
and other funky curcuits that often weren't fixing the tape or recorders
problems but some illness in the system cassette interface. The best
example of that was they TRS80. For example my fix for there interface
believe it or not was remove ALL the analog on the input side and drive
the gate z24 pin9 through a 10uf cap with a 270ohm pull down on the pin.

There were at least two articles with filter/amps and other circuits
all unneeded for that! Most all didn't usnderstand the interface or
the behavour of audio tape.

Allison
Received on Fri Nov 27 1998 - 14:38:46 GMT