math - Calculating a Web Audio API filter's response at a specific frequency and Q-factor

Question

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.

Answer 1

你看过 BiquadFilterNode 的 getFrequencyResponse 方法吗？ https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#Methods。

我的 IO2012 Web Audio 演讲中的这个演示使用了它：http ://webaudio-io2012.appspot.com/frames/frequency-response.html 。当然，您必须计算从那里堆叠在一起的多个过滤器的响应。