From mweber@delphi.com Mon Jun 24 01:31:24 1996
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!delphi!mweber
From: mweber@delphi.com (Morag Weber)
Newsgroups: comp.dsp
Subject: Data: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Jun24.013124.3198@delphi.com>
Date: Mon, 24 Jun 1996 01:31:24 GMT
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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.
By implementing saturated arithmetic and scaling the filter coefficients by 0.5, the loop runs in 18 instruction cycles per sample.

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

-- 
Morag Weber | mweber@delphi.com
PGP Key fingerprint: AF8B 897A C0AD F660
"Keep the channels open."

From gsantos@illinois.edu Tue Jun 25 20:18:24 1996
Path: ashpoly!cascade!bigsur!illinois!gsantos
From: gsantos@illinois.edu (Graham Santos)
Newsgroups: comp.dsp
Subject: Re: Data: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Jun25.201824.9636@illinois.edu>
Date: Tue, 25 Jun 1996 20:18:24 GMT
References: <1996Jun24.013124.3198@delphi.com>
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In article <1996Jun24.013124.3198@delphi.com>, mweber@delphi.com (Morag Weber) writes:
> 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.

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

My 14.4k connection dropped twice trying to fetch this thread. Keep articles concise!

-- 
Graham Santos -- University of Illinois Urbana-Champaign
"Hardware is temporary. The signal survives."

From mpark@mindspring.com Wed Jun 26 00:30:24 1996
Path: ashpoly!cascade!transat!ukc!fennimore!mindspring!mpark
From: mpark@mindspring.com (Marisol Park)
Newsgroups: comp.dsp
Subject: Re: Data: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Jun26.003024.6179@mindspring.com>
Date: Wed, 26 Jun 1996 00:30:24 GMT
References: <1996Jun24.013124.3198@delphi.com>
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In article <1996Jun24.013124.3198@delphi.com>, mweber@delphi.com (Morag Weber) writes:
> 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.

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

-- 
Marisol Park | mpark@mindspring.com
PGP Key fingerprint: F2CB 6847 8846 6E7C
"Keep the channels open."