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Re: Sony AGC confession

Subject: Re: Sony AGC confession
From: Aaron Ximm <>
Date: Tue, 12 Mar 2002 16:01:22 -0800 (PST)
> For those that are tempted to use the AGC aka ALC (automatic
> recording gain control) of a Sony MD or other recording device.

Out of curiosity, does anyone have comments on the automatic (true)
limiter on Sony PCM-M1 (aka TCD100?) DAT walkmen?

I've always avoided it, but read someone cautiously laudatory comments
about the feature when the deck was introduced -- it's supposed to
function as a transparent limiter, without doing any gain control
otherwise.  Clearly a last resort, but as I recall it did save a recording
or two...

Re: digital overs on MD -- I've done a lot of close-in wave reconstruction
on clipped recordings made with my MD portables, and have noticed
something very unusual... the "overs" aren't limited or squared off, they
simply flip polarity, producing an abberent 'transient' spike for a sample
or several.

This is a direct result of the binary encoding of negative numbers --
nothing you'd want to listen to, but it's interesting since it actually
*preserves* information.  The true waveform could (by the patient) be
reconstructed (assuming the total level was reduced up front, or the file
is converted to an editing space with headroom).  I haven't been so
disciplined;  instead I usually just eyeball in a curve by hand and call
it a day.

My roommate was quite fascinated by this, and commented that it's probably
a design corner having been cut post ADC in the MD -- he said most
convertor [chains] will square off the wave, but not let its polarity
flip, on overs.  Perhaps a property/feature/bug of the ADC chips
themselves...?

This quirk has further introduced me to some interesting discrepencies
between my various CD players and audio cards -- my personal stereo (it
seems) does *not* reproduce the inverted "transients", while my PC audio
card does. I.e. I can listen to a horrible-sounding clipped recording on
my PC, burn it to CD, and it will sound fine (with only a hint of
squared-off distortion) on my stereo.

Best regards,
aaron

  
  http://www.quietamerican.org



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