The syntax for biquad~'s arguments, according to the help patch: fb1 fb2 ff1 ff2 ff3
In the patch you swap fb2<>ff2 and ff1<>ff3. The syntax in the help file is confusing. For better consistency it could be called: fb1 fb2 ff0 ff1 ff2 Fill the coefficients for the 44.1 reproduction filter as mentioned in the musicdsp topic: -0.721892 -0.186052 1 -1.70072 0.702938 But this doesn't seem to produce a minimum phase filter, and it can't be inverted. I guess the signs of feedback coefficients must be flipped to match Pd's biquad implementation: 0.721892 0.186052 1 -1.70072 0.702938 This gives a frequency and phase response much resembling the plots on http://jiiteepee.tripod.com/riaa.html. This filter can be inverted by swapping the feedback and feed forward coefficients and also flipping the signs: 1.70072 -0.702938 1 -0.721892 -0.186052 This gives the exact inverse frequency and phase response. Katja On Wed, Oct 15, 2014 at 12:14 AM, me.grimm <[email protected]> wrote: > all the biquad talk had me remember trying to figure out the riaa filter > for vinyl playback/production a couple years back which i never quite > figured out. attached is what I had attempted. > > the playback filter seems to be correct but when I switch to the > production filter. which should be the inverse of the playback filter, i > get nothing but I think im swapping the coefficients incorrectly... > > anyway, here is the thread this is based off of: > > http://www.musicdsp.org/showone.php?id=122 > > and here is some help on the inverse: > > http://music.columbia.edu/pipermail/music-dsp/2003-February/055408.html > > maybe someone can make heads or tails of this and give me a help? > > basically I am attempting to 3d print a record cutting head so I mostly > need the production (iRIAA) filter as I will be going straight from PD to a > record lathe. > > thanks! > m > > ps. this was helpful too http://jiiteepee.tripod.com/riaa.html > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > >
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