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Filtering Audio

Mar 03 2012 | 10:22 pm

Hi, I’m playing an audio file (.aif file of a rock track) within a patch and I want to filter it so I just have frequencies between 95hz and 110hz remaining. I’ve been toying with reson~ and can’t get it to filter narrow enough. Does anybody know how I might do this successfully? Or at least as close as possible?



Mar 04 2012 | 1:02 am

what about a lowpass and high pass cascaded? or a different filter, biquad maybe? not really my area of expertise though

Mar 04 2012 | 1:09 am

Hi kanisi,

Use filtercoeff~ with biquad~ to filter the signal. The filtercoeff~ help patcher will show you how to do it.

But I’d add that you might not get very good results trying to filter down to a 15hz band in that manner. Taking an FFT and zeroing out the bins you’re not interested in might be a better solution, though it’s a much more complicated job.

Is there some reason you can’t do the filtering in an audio editor, and use the filtered file as input, rather than the full bandwidth?

Mar 04 2012 | 2:19 am

If you are on Max6, check out the filterdesign object. you can make high order butterworth and chebychev filter coeffecients for cascade~. If you are not on Max6, check out vb.chebychev~ ( Dream is right though that this could be tricky for 15Hz passband.

FFT solutions are not so tricky, but have other issues to consider. I’ve got to run out for a bit, but later tonight I’m actually doing some work on some patches like this, so I’ll send you an example.

Mar 04 2012 | 12:55 pm

Thanks guys, much appreciated. @dream I’m trying to do this in real time so can’t do it in an audio editor. @Roth that would be great, thanks so much. Really grateful for the help. I’ll look into your suggestions and let you know how I get on.

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Forums > MaxMSP