Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site lanl.ARPA
Path: utzoo!linus!decvax!genrad!wjh12!harvard!seismo!cmcl2!lanl!jlg
From: jlg@lanl.ARPA
Newsgroups: net.audio
Subject: Re: Floating Point CD's - (nf)
Message-ID: <15486@lanl.ARPA>
Date: Thu, 1-Nov-84 19:09:27 EST
Article-I.D.: lanl.15486
Posted: Thu Nov  1 19:09:27 1984
Date-Received: Sat, 3-Nov-84 21:30:27 EST
References: <1753@inmet.UUCP> <565@watdcsu.UUCP>
Sender: newsreader@lanl.ARPA
Organization: Los Alamos National Laboratory
Lines: 21

I've been thinking about floating point music representation for some time.
The best format seems to be 1 sign-bit, 3 (or 4) exponent bits, and 13 (or
12 ) significand bits.  The 3 bit exponent with a IEEE floating point type 
of gradual underflow and a hidden normalization bit gives a dynamic range
of about 120 db.  The signal to noise ratio is always about 78 db - that
is 78 db below present signal ( If I'm listening to a sound at 90 db, I
can't hear noises at 12 db  - I don't think anyone else can either).

The 4 bit exponent format has a dynamic range of over 160 db, with a signal
to noise ratio of about 70 db.  This is beyond the dynamic range of human
hearing - should be sufficient.  It is also beyond the dynamic range of current
recording techniques, the widest A/D I've seen with the ability to run the
speeds required for audio recording were 18 bits (several thousand $).  
The four bit exponent format is suitable for compression of 28 bit data,
I don't think we'll ever see that!  

Both the 3 bit and 4 bit exponent formats given here require 16 bits of
space on the recording medium.  That makes them compatible with the
current data encoding, error reduction schemes.  The only thing required
is circuitry to convert such floating point numbers into integers for
the D/A conversion.