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Frequency Ranges For Shelving Filters in L/M/H EQ?

August 7, 2008 | 6:12 pm

Hi, I am interested in creating a simple EQ for low/mid/high, similar to what one might find on a DJ’s mixing board. I’ve gone about creating this through 3 biquad/filtergraph combinations, one lowpass, one bandpass, one highpass. My frequencies for each respective filter are 200, 500, and 1500. However, comparing the signal that gets passed through these filters, even when all their gains are at 1, to the original signal, I found the filtered signal to be missing some frequencies, particularly in the low range. I was hoping someone would have recommendations for the frequency that each filter should be set at, or possibly a different approach to creating this kind of EQ.

Thanks!


August 7, 2008 | 6:24 pm

It may have more to do with the Q/bandwidth of the filter.

You might try, instead, low-shelf(not lowpass), peak-notch, and then high-shelf.

All of these would move between a gain of 1 to negative gain so it might emulate the dj-mixer style eqs better.

Then, you could look something like hearing ranges up in Computer Music Tutorial by Curtis Roads who has some good ideas about the sensitivity of the human ear to various frequencies. I probably won’t remember correctly, but I thought it was something like 200Hz for low sensitivity, 1k for mid-range, and 5k and above for the hights (but then he has others which really hit your ear hard in some ways and advises trying to use bandpass to find them(i think one of them was 10k which is really harsh but then above 12k and you’ll get a nice sparkle). But ya, try 200, 1000, and 5000 and then work from there to see what you like/think. I’m not going to quote him lest I do his genius complete injustice.

Hope it helps.


August 7, 2008 | 6:29 pm

Oh, and if you do want low-pass high-pass instead of shelving filters, try (a series of them). Might be another option. Otherwise, the help-file for filtergraph~ tells you most of what you need for biquad~ control.


August 7, 2008 | 7:24 pm

thanks for the help raja, lowshelf/highshelf/peaknotch are all much better choices for what im looking for.


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