From aoliveira@delphi.com Sun Mar 26 01:37:36 1995 Path: ashpoly!cascade!transat!eunet-fr!teletel!delphi!aoliveira From: aoliveira@delphi.com (Amy Oliveira) Newsgroups: comp.dsp Subject: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995Mar26.013736.8768@delphi.com> Date: Sun, 26 Mar 1995 01:37:36 GMT Organization: Delphi Internet Services NNTP-Posting-Host: delphi.com X-Newsreader: NewsWatcher 2.0b24 Lines: 11 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. However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop. Source code in 56k assembly uploaded to ftp.ashford-poly.edu:/pub/telecom-archives/dsp56k/stardust_56k.asm. -- Amy Oliveira Hayes Optima 288 @ ISDN 64k bps "We don't sign stars. We build them." From dfischer@kth.se Sun Mar 26 07:13:36 1995 Path: ashpoly!bigsur!pacrim!krgate!eunha!kth!dfischer From: dfischer@kth.se (Dmitri Fischer) Newsgroups: comp.dsp Subject: Re: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995Mar26.071336.8796@kth.se> Date: Sun, 26 Mar 1995 07:13:36 GMT References: <1995Mar26.013736.8768@delphi.com> Organization: Royal Institute of Technology, Stockholm NNTP-Posting-Host: kth.se X-Newsreader: Netscape 1.1N Lines: 9 In article <1995Mar26.013736.8768@delphi.com>, aoliveira@delphi.com (Amy Oliveira) 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. -- Dmitri Fischer *PLONK* filter active for trolls. PC-9821Ap2 (NEC) - NetBSD 1.0