Forums > MaxMSP

Subwoofer crossover strategies?


dtr
November 26, 2009 | 9:59 am

Hi,

I am preparing a surround audio performance and want to create a 4.1 monitoring setup in my studio. Budget ‘s limited though. Subs I can afford don’t have multichannel support, just stereo, so I’ve been looking for workarounds. There are external surround bass management devices but they are as expensive as subs with surround support so no go. Next idea is to do the crossover filtering in Max.

I’m a noob when it comes to signal processing theory so I’m looking for advice on what way to go. I looked at documentation like http://en.wikipedia.org/wiki/Audio_crossover but lots of questions remain.

Will parallel high-pass and low-pass biquad~’s do? Those have 12dB slopes if I understand correctly. But in the documentation of the Blue Sky bass management controller I read the high-pass is 12dB and the low-pass 24dB. What’s up with that?

Should I worry about phase alignment and other things?

Or is an FFT based approach more desirable?

Tanx for all help!


November 26, 2009 | 5:29 pm

I’d look at svf~, and not worry about phase unless you’ve got some serious sound system and acoustic treatment in your studio.


November 26, 2009 | 9:22 pm

linkwitz riley crossover filters are useful to transparently split the signal. http://en.wikipedia.org/wiki/Linkwitz-Riley_filter

it’s been a while since i last looked into it, but IMO phase is important as is filter design if you want to avoid colouring the signal or causing potential acoustic problems. ultimately, i guess it depends on how accurately you need to depict the spatial experience.

i seem to remember 3rd party butterworth filter externals existing somewhere on the web, these might come in handy to make a crossover… not sure if biquad~ is suitable.

hth,

j



dtr
November 27, 2009 | 12:14 pm

thanks for the tips, will look them up.

in the meanwhile i tried some things with biquad. 2 biquad’s chained (24db total) for both HP and LP filters gets quite close. there’s a bit of coloring though, heard on some bass audio material. i tested by switching audio signals between unprocessed and summed HP and LP filtered signals, monitoring on Beyer Dynamic DT990 headphones.

@mzed: my studio setup isn’t very impressive but the systems when playing out might…


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