[PD] biquad~ based riaa filter

[me.grimm]

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
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