Multiple frequency crossovers

Erez Blumestock

Hi all!

I'm teaching about equalisers and I'm trying to split the spectrum of a signal to multiple frequency ranges, that could be determined by the user.

Crossover~ can do the job pretty well to split the signal to two, but I'm looking for a way to split the signal to a number of bandwidths (around 4-8). combining a number of crossovers resulted with phasing issues.

I tried to use pfft~ as explained in the tutorials, but there is no rolloff between the bands and I want it to resemble a parallel filtering eq.
pfft~ is a bit complicated for me, so if anyone has any idea how to make it with pfft~ I would love to hear!

So… what will be the best way to split a signal to multiple bands, all in phase, and made with smooth transitions between one band to the other.

Thanks much! Erez.

Peter McCulloch

If you want them to maintain their phase, then you would probably need to look at FIR filters.

You can design these using the inverse FFT (Ifft~) by inputting the desired amplitude response characteristics, capturing the resulting waveform, then mirroring it on the time axis. Making it symmetric in this fashion will make the result linear in phase response. (It's been awhile since I was fiddling with this, but you may have to half the amplitude drop since you are filtering it twice). Then use buffir~ to perform the convolution.

When I did it, I used the Google JS FFT instead of doing it with signals.

All that said, this could get a bit hairy in a pedagogical context...