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From: schooler@inmet.UUCP
Newsgroups: net.audio
Subject: Re: Floating Point CD's
Message-ID: <1765@inmet.UUCP>
Date: Sun, 28-Oct-84 03:36:58 EST
Article-I.D.: inmet.1765
Posted: Sun Oct 28 03:36:58 1984
Date-Received: Tue, 30-Oct-84 00:44:49 EST
Lines: 18
Nf-ID: #R:inmet:2600114:inmet:2600116:000:1072
Nf-From: inmet!schooler    Oct 26 10:38:00 1984

As someone pointed out, a 16-bit floating-point representation is over-kill.
(Who needs > 150 dB?!) Consider, however, an 8-bit logarithmic
representation, as proposed by Edgar and Lee in "FOCUS Microcomputer Number
System", Comm. ACM, Vol. 22, Num. 3, March 1979.  This representation has
one sign bit and a seven-bit exponent in fixed-point format with three
fraction bits.  The sign of the exponent is encoded by an offset, i.e. 0
1000.000 = +2^0 = 1.  The authors claim a range of 96 dB, an absolute S/N of
93 dB, and an instantaneous S/N (precision, roughly) of 32 dB.  I quote, "In
audio applications the noise level of even the 8-bit FOCUS compares
favorably to the highest quality cassette recordings as a means of signal
handling."  Furthermore, they suggest a simple circuit for logarithmic A-D's
and exponential D-A's.  While addition and subtraction are to be avoided,
multiplication, division and exponentiation are fast and exact.  If all this
is really valid, we can cram twice as much sound per bit onto our favorite
digital medium.

		-- Richard Schooler