Baxandall filter for Max/MSP?
Hi, I need to create a Baxandall filter (e.g., generic tone control) in Max/MSP and am surprised to find nothing on it here. Is there a simple way to do this?
Three years later and nothing.
Well, wish me luck. I'm trying to do this in gen~
I'll try to remember to post my findings
I expect that the reason you haven't seen anything is that the Badandall is an analog filter. Producing digital versions of analog filters is by no means a straight-ahead operation. If you're interested in pursuing it, you may find this article to be of some assistance as a starting-point:
you can use biquad with butterworth flavour, that should be the closest and shortest path and that´s what they use in their VSTs - but i have no idea how to make a shelving filter with that topology.
i dont know any hardware effect either, sometimes i wish that passive "impedance" control from my yamaha hifi amp would be available as insert effect.
The thing you're looking for are first-order shelving filters. You can find formulas for those here:
http://freeverb3vst.osdn.jp/doc/AN11.pdf
You can implement those using biquad~, or gen~.
I also naively typed "Baxandall" into the forum search recently and got only this post.
That paper Peter mentioned is very good. However I lazily did not follow it and came up with the following (comparing a 'real' Baxandall to a simple first order shelving EQ I already had):
one of the differences between the original baxandall tone stack and other recursive filters with poles and zeros is that the b. uses negative feedback at some point. this is what makes the slope broader and why the filters in guitar amps sounds so different from most mixing desks.
give that both, bax and biquad, are from around 1950 and every second hifi stereo and two out of three mastering EQs are using bax, it is a joke that you can hardly find a proper analysis of the historic models.
for the original model you need 3 poles and 3 zeroes and it should be possible to implement each of the parts with with 2 parallel biquad objects in a polyphase approach, but i never got it to work because i never really understood the few schematics you can find.
my own "tone control" plug-in always only used simple butterworths to contruct shelving filters from and then leave the numbers to the user.