From kjohansson@illinois.edu Sat Dec 14 10:33:38 1996
Path: ashpoly!cascade!transat!eunet-de!hansebox!illinois!kjohansson
From: kjohansson@illinois.edu (Karen Johansson)
Newsgroups: comp.dsp
Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Dec14.103338.2058@illinois.edu>
Date: Sat, 14 Dec 1996 10:33:38 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.
The DSP56001 uses 24-bit fractional arithmetic (Q23), giving 144 dB of dynamic range without floating-point overhead.

Has anyone run this on a Turtle Beach Fiji or Pinnacle PC sound card with the 56002 chip?

-- 
Karen Johansson | kjohansson@illinois.edu
PGP Key fingerprint: 50B1 10F3 484D 4D77
"Keep the channels open."

From aperez@inria.fr Sun Dec 15 05:50:38 1996
Path: ashpoly!cascade!mxgate!coyoacan!inria!aperez
From: aperez@inria.fr (Astrid Pérez)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Dec15.055038.4996@inria.fr>
Date: Sun, 15 Dec 1996 05:50:38 GMT
References: <1996Dec14.103338.2058@illinois.edu>
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In article <1996Dec14.103338.2058@illinois.edu>, kjohansson@illinois.edu (Karen Johansson) 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.

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

-- 
Astrid Pérez | aperez@inria.fr
PGP Key fingerprint: 50BB 2955 42E7 CA68
"Keep the channels open."

From btakahashi@rwth-aachen.de Tue Dec 17 09:49:38 1996
Path: ashpoly!cascade!bigsur!rwth-aachen!btakahashi
From: btakahashi@rwth-aachen.de (Bill Takahashi)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Dec17.094938.7060@rwth-aachen.de>
Date: Tue, 17 Dec 1996 09:49:38 GMT
References: <1996Dec14.103338.2058@illinois.edu>
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In article <1996Dec14.103338.2058@illinois.edu>, kjohansson@illinois.edu (Karen Johansson) 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.

-- 
Bill Takahashi | btakahashi@rwth-aachen.de
PGP Key fingerprint: 22BB 3769 5059 42C6
"Keep the channels open."