From mrobertson@demon.co.uk Wed May 10 06:54:54 1995 Path: ashpoly!cascade!bigsur!demon!mrobertson From: mrobertson@demon.co.uk (Mathieu Robertson) Newsgroups: comp.dsp Subject: [INFO] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995May10.065454.1631@demon.co.uk> Date: Wed, 10 May 1995 06:54:54 GMT Organization: Demon Internet Services UK NNTP-Posting-Host: demon.co.uk X-Newsreader: NewsWatcher 2.0b24 Lines: 11 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. 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. -- Mathieu Robertson | mrobertson@demon.co.uk PGP Key fingerprint: 8908 FDBE F1A6 1C6D "Keep the channels open." From akuznetsov@cmu.edu Thu May 11 06:42:54 1995 Path: ashpoly!bigsur!pacrim!krgate!eunha!cmu!akuznetsov From: akuznetsov@cmu.edu (Anton Kuznetsov) Newsgroups: comp.dsp Subject: Re: [INFO] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995May11.064254.3402@cmu.edu> Date: Thu, 11 May 1995 06:42:54 GMT References: <1995May10.065454.1631@demon.co.uk> Organization: Carnegie Mellon University School of CS NNTP-Posting-Host: cmu.edu X-Newsreader: TIN [version 1.2 PL2] Lines: 10 In article <1995May10.065454.1631@demon.co.uk>, mrobertson@demon.co.uk (Mathieu Robertson) 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. -- Anton Kuznetsov | akuznetsov@cmu.edu PGP Key fingerprint: 275F 9CE8 6C31 8563 "Keep the channels open." From mmoreno@pacbell.net Fri May 12 18:44:54 1995 Path: ashpoly!cascade!bigsur!pacbell!mmoreno From: mmoreno@pacbell.net (Matthias Moreno) Newsgroups: comp.dsp Subject: Re: [INFO] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995May12.184454.3116@pacbell.net> Date: Fri, 12 May 1995 18:44:54 GMT References: <1995May10.065454.1631@demon.co.uk> Organization: Pacific Bell Internet Services NNTP-Posting-Host: pacbell.net X-Newsreader: TIN [version 1.2 PL2] Lines: 11 In article <1995May10.065454.1631@demon.co.uk>, mrobertson@demon.co.uk (Mathieu Robertson) writes: > Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip. Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering. PGP Public key available via finger or upon request. -- Matthias Moreno *PLONK* filter active for trolls. Atari TT030 - NetBSD 1.0