Splitting frequencies in PatchWork

[force_redo]

Hi,

I was wondering whether I can split out frequency bands in PatchWork and sum them together again.

What I'm trying to do is make a little setup that allows me to control stereo width by frequency band. Nothing groundbreaking, I know, I was just wondering whether I can implement it in PatchWork.
I know I can use the EQ module to high/low/band pass certain frequencies and process them in parallel and sum them together again, but what I don't know is:

a.) can I control one eq with another, e.g. can I move a high pass frequency and it will also control the low pass frequency of another eq? I.e. have one button for a crossover frequency?

b.) I don't know what the maths is behind summing frequency bands.
Say, I high pass a signal at 200hz with a 24dB/oct filter. If I want to low pass the same signal with a 24dB/oct filter, what does the frequency have to be set to, so the two will sum together to become the original signal again? Or is this not possible?

c.) Maybe there is an easier way of achieving this? (yes, I can stick third party plugins in, but where's the fun in that? I was considering buying plug ,n, script or synthedit, but can't get myself to learning another scripting language)

Thanks for reading!

[Blue Cat Audio]

Band splitting with an EQ is a bit challenging because it will affect the phase of each parallel chain deifferently, so when you sum them back together, it will result in heavy comb filtering.

So you either need to use linear phase filters or compensate the phase, but the latter is almost impossible without using filters that were specifically designed for this purpose.

That's why we have created the MB-7 Mixer plugin: it just does the band splitting and phase compensation for you, and you can easily insert plug-ins for each band or use the built-in controls (it already has stereo width controls for each band):

[rrichard63]

It's good to know that MB-7's filters have some sort of phase compensation. Although I own MB -7, I have been reluctant to use it very much because it has no option to choose linear phase filters. My preference has been to use Patchwork with linear phase EQs as filters in each parallel chain.

Can you say anything (or point us to published discussions) about how the phase compensation works? I wasn't aware that there is such a thing. Thanks!

[Blue Cat Audio]

The MB-7 Mixer plug-in indeed does not have linear phase filters for the moment, so it does not alter the phase of frequencies exactly the same way (some frequencies are delayed more than others, depending on the crossover settings), but it does not have latency.

However all bands sum properly because phase is compensated: it means that the phase shift is exactly the same on all bands, so that they sum up to unity. You would get comb filtering otherwise. On each band we apply specific phase shifting so that it is the same as for all other bands that have been affected by other crossovers. It is a common practice for multiband processors with minimum phase crossovers.

[rrichard63]

Thank you for the helpful explanation.

[force_redo]

I also wanted to say thanks. Very interesting indeed.