great thanks for the help! that seems to work swell.... attached is the revision.

how would one go about generating / calculating the coefficients in pd using [expr]? then instead of having each in its own message the coefficients could be calculated automatically via global/local sample rate, normalizing gain could be applied/adjusted in real-time, etc.

m



On Wed, Oct 15, 2014 at 7:59 AM, katja <katjavetter@gmail.com> wrote:
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 <megrimm@gmail.com> 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:


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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