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From: shauns@vice.UUCP (Shaun Simpkins)
Newsgroups: net.audio
Subject: Re: Controlled compression, etc
Message-ID: <50@vice.UUCP>
Date: Wed, 17-Oct-84 12:25:32 EDT
Article-I.D.: vice.50
Posted: Wed Oct 17 12:25:32 1984
Date-Received: Sun, 21-Oct-84 12:40:38 EDT
References: <86@azure.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 38


Controlled compression of CDs was proposed as a means of getting 20-bit
effective dynamic range out of CDs without building a 20-bit digitizer, which
is very difficult to build.  I stated that CDs have a noise floor that is
below the average listening room's but above hearing threshold.  By increasing
the dynamic range of the system we improve the reproduction of near-threshold
level signals.  IF the ear can discern 8 or 10 bit quantization at such low
levels (which I don't think it can) compansion will shove the signal level up
to a point where the resolution is higher.  The use of a control track
for gain riding eliminates the envelope tracking error of present compansion
systems.  I agree that preceeding a digital recorder with a dbx unit is
pointless from a distortion point of view.

I think the real issue in this conversation was not `is the CD inferior' which
I think it isn't for home use, but `what should be the professional quality
level', over which there is some reasonable concern.  I am concerned over
the blanket approval of digital techniques as a panacea to the problems of
multi-track mixdowns. It isn't.  Let's take an example - we have two 16bit
digital words.  The LSB of both fluctuates randomly (i.e., the noise floor
of the digitizer is equal to 1 LSB).  We now add them together.  Oops! The
2nd LSB is dithering, too.  The noise floor has moved up from 1/2 LSB average
to 1 LSB average. Do this a few times and you've lost a lot of your
resolution to noise.

My point?  If recordists are not to sacrifice their beloved multitrack
techniques for minimalist recording methods (I doubt that they will) the
recorders they use must be better than our players.  This means more bits or
a noise floor of the recording system before the sampler of much, much less
than the digitizer's resolution.  Compansion is a way of achieving this
with present systems.

The wandering squash,
-- 
				Shaun Simpkins

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