have you seen this? I am not an expert in ffts so maybe it could be improved but it is impressively fast in my experience (also very readable) : https://github.

have you seen this? I am not an expert in ffts so maybe it could be improved but it is impressively fast in my experience (also very readable) : https://github.com/corbanbrook/dsp.js/blob/master/dsp.js https://github.com/corbanbrook/dsp.js/blob/master/dsp.js