[PD] biquad~ based riaa filter

[me.grimm]

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 at 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 at 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:
>>
>> 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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>
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