Web audio API equalizer

Question

I have been looking around for creating an audio equalizer using the Web audio API: http://webaudio.github.io/web-audio-api/

I found a lot of threads about creating a vi

Answer 1

Multiple things here.

1) You shouldn't use bandpass filters in parallel to implement an equalizer. Among other issues, biquad filtering changes the phase of different parts of the signal, and therefore the different bands will end up in different phases, and you'll have some potentially quite bad effects on your sound when it recombines.

2) The approach that you want is have a low shelf filter on the bottom end, a high shelf filter on the top end, and any number of peaking filters in the middle. These should be connected in series (i.e. the input signal connects to one filter, which connects to another filter, which connects to another filter, et al, and only the final filter should get connected to the audiocontext.destination. The Q values should be tuned (see below), and the gain on the filter determines the boost/cut. (For flat response, all filter gains should be set to zero.)

3) filter.type is an enumerated type that you should set as a string, not as a number. "lowshelf", "highshelf" and "peaking" are the ones you're looking for here.

You can see an example of a simple three-band equalizer in my DJ app - https://github.com/cwilso/wubwubwub/blob/MixTrack/js/tracks.js#L189-L207 sets it up. To modify this into a multiband equalizer, you'll need to tweak the Q value of each filter to get the bands to not overlap too much (it's not bad if they do overlap, but your bands will be more precise if you tune them). You can use http://googlechrome.github.io/web-audio-samples/samples/audio/frequency-response.html to examine the frequency response for a given Q and filter type.