Calculating a Web Audio API filter's response at a specific frequency and Q-factor
audio, canvas, math, signal-processing, web-audio-api
Solution
Have you looked at the getFrequencyResponse method of BiquadFilterNode? https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#Methods.
This demo from my IO2012 Web Audio talk uses it: http://webaudio-io2012.appspot.com/frames/frequency-response.html. You'll have to calculate the responses of multiple filters stacked together from there, of course.
Problem
I'm using the Web Audio API to make a graphic EQ with four BiQuad filters; a highpass, two bandpass and a low pass: You can see each node representing each filter's frequency. It's working nicely but I'd like to draw the shape of the filter's roll-off you'd usually find in other graphic EQ's. I have the Q-factor of each filter and the central frequency. What I would like to do is get a formula that allows me to get the frequency of the roll-off at a specific db value. For example what is the frequency of the roll-off at -200db? It's been a while since I've done any heavy mathematical stuff and so any help would be greatly appreciated.