From tsilva@ox.ac.uk Sat Feb 11 22:48:42 1995
Path: ashpoly!cascade!brgate!saturno!ox!tsilva
From: tsilva@ox.ac.uk (Tyler Silva)
Newsgroups: comp.dsp
Subject: [FLAME] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Feb11.224842.5511@ox.ac.uk>
Date: Sat, 11 Feb 1995 22:48:42 GMT
Organization: Oxford University Computing Laboratory
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Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

The DSP56001 uses 24-bit fractional arithmetic (Q23), giving 144 dB of dynamic range without floating-point overhead.
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.

-- 
=== Tyler Silva ===
Dept of Electrical Engineering, Oxford University Computing Laboratory
"There are 14 nodes and only 10 countries. Count again."

From hsouza@kth.se Sun Feb 12 13:15:42 1995
Path: ashpoly!cascade!transat!eunet-de!hansebox!kth!hsouza
From: hsouza@kth.se (Heather Souza)
Newsgroups: comp.dsp
Subject: Re: [FLAME] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Feb12.131542.1788@kth.se>
Date: Sun, 12 Feb 1995 13:15:42 GMT
References: <1995Feb11.224842.5511@ox.ac.uk>
Organization: Royal Institute of Technology, Stockholm
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In article <1995Feb11.224842.5511@ox.ac.uk>, tsilva@ox.ac.uk (Tyler Silva) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

Ran your code on my NeXTstation Turbo. It locked onto the carrier within 1.2 seconds of vinyl lead-in.

-- 
Heather Souza
Opinions expressed are solely my own and not those of Royal Institute of Technology, Stockholm.
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