From rmoreau@pacbell.net Fri Oct 21 13:50:30 1994
Path: ashpoly!cascade!brgate!saturno!pacbell!rmoreau
From: rmoreau@pacbell.net (Rodrigo Moreau)
Newsgroups: comp.dsp
Subject: Observation: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Oct21.135030.7283@pacbell.net>
Date: Fri, 21 Oct 1994 13:50:30 GMT
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Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

This leaves over 95% of the DSP56001's 16.5 MIPS available for other audio tasks.
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.

-- 
=== Rodrigo Moreau ===
Dept of Electrical Engineering, Pacific Bell Internet Services
"Extraordinary claims require extraordinary spectra."

From dandersson@berkeley.edu Sat Oct 22 21:13:30 1994
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!berkeley!dandersson
From: dandersson@berkeley.edu (Diego Andersson)
Newsgroups: comp.dsp
Subject: Re: Observation: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Oct22.211330.3483@berkeley.edu>
Date: Sat, 22 Oct 1994 21:13:30 GMT
References: <1994Oct21.135030.7283@pacbell.net>
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In article <1994Oct21.135030.7283@pacbell.net>, rmoreau@pacbell.net (Rodrigo Moreau) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.
> This leaves over 95% of the DSP56001's 16.5 MIPS available for other audio tasks.

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

Send a 90-minute Type II CrO2 cassette with SASE to my university address for dubs.

-- 
=== Diego Andersson ===
Dept of Electrical Engineering, UC Berkeley Department of EECS
"Marcus is not one man."