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.