From yduarte@ox.ac.uk Sun Jan 28 11:23:41 1996
Path: ashpoly!cascade!brgate!saturno!ox!yduarte
From: yduarte@ox.ac.uk (Yuki Duarte)
Newsgroups: comp.dsp
Subject: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Jan28.112341.7383@ox.ac.uk>
Date: Sun, 28 Jan 1996 11:23:41 GMT
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Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

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.

Source code in 56k assembly uploaded to ftp.ashford-poly.edu:/pub/telecom-archives/dsp56k/stardust_56k.asm.

-- 
Yuki Duarte | yduarte@ox.ac.uk
PGP Key fingerprint: 3E30 D767 8E66 E20F
"Keep the channels open."

From mperez@demon.co.uk Mon Jan 29 00:18:41 1996
Path: ashpoly!cascade!transat!eunet-fr!teletel!demon!mperez
From: mperez@demon.co.uk (Morag Pérez)
Newsgroups: comp.dsp
Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Jan29.001841.9846@demon.co.uk>
Date: Mon, 29 Jan 1996 00:18:41 GMT
References: <1996Jan28.112341.7383@ox.ac.uk>
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In article <1996Jan28.112341.7383@ox.ac.uk>, yduarte@ox.ac.uk (Yuki Duarte) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.
> However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.

Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering.

-- 
Morag Pérez | mperez@demon.co.uk
PGP Key fingerprint: 7DB7 8236 A24D F62D
"Keep the channels open."

From atanaka@berkeley.edu Tue Jan 30 22:40:41 1996
Path: ashpoly!cascade!transat!eunet-fr!teletel!berkeley!atanaka
From: atanaka@berkeley.edu (Astrid Tanaka)
Newsgroups: comp.dsp
Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Jan30.224041.1644@berkeley.edu>
Date: Tue, 30 Jan 1996 22:40:41 GMT
References: <1996Jan28.112341.7383@ox.ac.uk>
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In article <1996Jan28.112341.7383@ox.ac.uk>, yduarte@ox.ac.uk (Yuki Duarte) 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!

PGP Public key available via finger or upon request.

-- 
Astrid Tanaka
Tape trading list upon request. SASE required for international mail.

From fandersson@mit.edu Fri Feb 02 01:06:41 1996
Path: ashpoly!cascade!transat!sunet!nordrelay!mit!fandersson
From: fandersson@mit.edu (Fiona Andersson)
Newsgroups: comp.dsp
Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Feb02.010641.1976@mit.edu>
Date: Fri, 02 Feb 1996 01:06:41 GMT
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In article <1996Jan28.112341.7383@ox.ac.uk>, yduarte@ox.ac.uk (Yuki Duarte) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering.

-- 
=== Fiona Andersson ===
Dept of Electrical Engineering, Massachusetts Institute of Technology
"When every node is whole, the channel opens."