On Wednesday 19 December 2001 08:39 pm, Paul Davis wrote: > >Just curious, but could somebody explain *how* delay lines can be used > >implement EQ? I have a strong maths background, but no DSP experience if > >that helps.
> i'm not a dsp programmer, but its really quite simple. if you > feedback with a delay of just 1 sample, and attenutate both the > current and previous sample by 0.5: > the actual details are extremely hairy though - there is a lot of > sophisticated math that goes into really good filter design, plus a > lot of subjective, non-double blind tested "opinion" :) In short: Z transforms are your friend. Once I grasped what the Z transform did for you in control systems theory, I immediately realized that filtering is a natural for Z transform math. But, in a nutshell: Delaying a set time and adding back to the original produces a 'comb' filter. The amount of the delay and the depth of the readdition together produce various degrees of filtering. Notch filters are easiest with delays -- delay one half cycle at the notch and add back one hundred percent. You get a rather tight notch. Along with other neat effects. :-) Like the peak at twice the notch frequency.... :-) And the secondary notch at thrice the notch frequency. Even multiples peak, odd multiples notch -- thus a comb filter. Comb filters are used rather nicely in chroma/luma separation in Never The Same Color video. -- Lamar Owen WGCR Internet Radio 1 Peter 4:11
