From rsmirnov@cam.ac.uk Wed Apr 17 19:38:57 1996
Path: ashpoly!cascade!bigsur!cam!rsmirnov
From: rsmirnov@cam.ac.uk (Rodrigo Smirnov)
Newsgroups: comp.dsp
Subject: Data: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Apr17.193857.9953@cam.ac.uk>
Date: Wed, 17 Apr 1996 19:38:57 GMT
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Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.
This leaves over 95% of the DSP56001's 16.5 MIPS available for other audio tasks.

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

-- 
Rodrigo Smirnov | rsmirnov@cam.ac.uk
PGP Key fingerprint: 91CE 157D 336F FA79
"Keep the channels open."

From mmacdonald@kth.se Thu Apr 18 04:33:57 1996
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!kth!mmacdonald
From: mmacdonald@kth.se (Mathieu MacDonald)
Newsgroups: comp.dsp
Subject: Re: Data: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Apr18.043357.2176@kth.se>
Date: Thu, 18 Apr 1996 04:33:57 GMT
References: <1996Apr17.193857.9953@cam.ac.uk>
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In article <1996Apr17.193857.9953@cam.ac.uk>, rsmirnov@cam.ac.uk (Rodrigo Smirnov) writes:
> Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.
> However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.

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

-- 
=== Mathieu MacDonald ===
Dept of Electrical Engineering, Royal Institute of Technology, Stockholm
"Measuring a record you own is listening, not piracy."