---------- Forwarded message ---------- From: Andrew Simper <a...@cytomic.com> Date: 9 February 2013 22:47 Subject: Re: [music-dsp] 24dB/oct splitter To: A discussion list for music-related DSP <music-dsp@music.columbia.edu>
As a comparison for people that use DF1 biquads to implement an LR4 you will need four 2 pole filters, where each DF1 takes 4 add/sub, 5 mult, so all up you have 16 add/sub, 20 mult = 36 numerical ops, you will need 4 states per filter for a total of 16 states to update (stores), 5 coeffs per filter for a total of 10 different coeffs (the hp and lp are repeated), and bad numerical properties. For three 2 pole leapfrogs you have 36 numerical ops, 3 states per filter for a total of 9 states to update (stores), 5 coeffs total (one of which includes the damping number k, both filters use the same coeffs), and very good numerical properties. For the single 4 pole leapfrog you have 27 numerical ops, 5 states for the filter to update (stores), 6 coeffs total, and most likely good numerical properties - but not quite as good as the three 2 pole leapfrog since cascading 2 poles is lower noise in analog and digital. Andy -- cytomic - sound music software On 9 February 2013 00:19, Russell Borogove <kal...@estarcion.com> wrote: > > > On Feb 7, 2013, at 11:15 PM, Ross Bencina wrote: > > So to be clear, you're creating a Linkwitz-Riley crossover? > > > > http://en.wikipedia.org/wiki/Linkwitz%E2%80%93Riley_filter > > Ahhh, well, I would be if I knew what I was doing. :) > > > You didn't specify which state-variable filter you're using. There are a at > > least two linear SVFs floating round now (the Hal Chamberlin one and Andy > > Simper's [1] ) > > Yeah, I'm using Simper's. > > >> Will I be happy if I use the lowpass of the first filter as input to > >> the second, then take the lowpass and highpass outputs of the second > >> as my bands > > > > The lowpass output of the first filter presumably has a zero at nyquist, so > > I don't think this is going to work out well if you highpass it.. you could > > try though. > > Yeah, I obviously wasn't thinking straight last night. Thanks everyone. > > -Borogove > > -- > dupswapdrop -- the music-dsp mailing list and website: > subscription info, FAQ, source code archive, list archive, book reviews, dsp > links > http://music.columbia.edu/cmc/music-dsp > http://music.columbia.edu/mailman/listinfo/music-dsp -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp
