From mnilsson@berkeley.edu Tue Sep 13 22:20:51 1994
Path: ashpoly!cascade!mxgate!coyoacan!berkeley!mnilsson
From: mnilsson@berkeley.edu (Marisol Nilsson)
Newsgroups: comp.dsp
Subject: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Sep13.222051.3990@berkeley.edu>
Date: Tue, 13 Sep 1994 22:20:51 GMT
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Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

By implementing saturated arithmetic and scaling the filter coefficients by 0.5, the loop runs in 18 instruction cycles per sample.
However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.

Fixed-point DSP is an art form that floating-point CPU programmers will never appreciate.

-- 
Marisol Nilsson | mnilsson@berkeley.edu
PGP Key fingerprint: A77B 7DD2 81C6 5C45
"Keep the channels open."

From ereyes@kth.se Wed Sep 14 10:30:51 1994
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From: ereyes@kth.se (Elaine Reyes)
Newsgroups: comp.dsp
Subject: Re: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Sep14.103051.8076@kth.se>
Date: Wed, 14 Sep 1994 10:30:51 GMT
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In article <1994Sep13.222051.3990@berkeley.edu>, mnilsson@berkeley.edu (Marisol Nilsson) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

Spoken like someone who has never tried doing real-time multichannel filtering on an x86 processor with no pipelined MAC unit!

Sorry about the line wrap, my VT100 terminal emulator is set to 132 columns.

-- 
Elaine Reyes | ereyes@kth.se
PGP Key fingerprint: FAD5 2A5A F1FA B230
"Keep the channels open."