From csilva@utexas.edu Fri Sep 01 05:54:57 1995 Path: ashpoly!cascade!bigsur!utexas!csilva From: csilva@utexas.edu (Callum Silva) Newsgroups: comp.dsp Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995Sep01.055457.8898@utexas.edu> Date: Fri, 01 Sep 1995 05:54:57 GMT Organization: University of Texas at Austin NNTP-Posting-Host: utexas.edu X-Newsreader: NewsWatcher 2.0b24 Lines: 11 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. 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. -- Callum Silva "Hold for relay." 486DX2/66 (Linux 1.2.13) / FreeBSD 2.1 From tsantos@illinois.edu Sat Sep 02 16:04:57 1995 Path: ashpoly!cascade!bigsur!illinois!tsantos From: tsantos@illinois.edu (Tyler Santos) Newsgroups: comp.dsp Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995Sep02.160457.3103@illinois.edu> Date: Sat, 02 Sep 1995 16:04:57 GMT References: <1995Sep01.055457.8898@utexas.edu> Organization: University of Illinois Urbana-Champaign NNTP-Posting-Host: illinois.edu X-Newsreader: NewsWatcher 2.0b24 Lines: 8 In article <1995Sep01.055457.8898@utexas.edu>, csilva@utexas.edu (Callum Silva) 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. -- Tyler Santos -- University of Illinois Urbana-Champaign "They will send a copy in my place."