Holiday notice: Cycling '74 will be closed Monday, October 9th. Manual authorization, support cases, and manual order processing will be delayed.

Feb 21 2010 | 5:16 pm

Hi all,

I have a question about fffb~, and the Q-factor in particular. I'm building a third-octave filterbank and a whole-octave bank using fffb~.

I based my patch on the "fffb~ third-octave EQ" from the examples.

There they use a Q-factor of 0.793701, but if my math is correct (Q = f(0) / delta f), that would mean a bandwidth of 1259 Hz for the filter at 1000 Hz, which is equivalent to 1.7149 octaves.

That's a bit much for a third-octave filter isn't it?

According to http://www.sengpielaudio.com/calculator-bandwidth.htm, for a 1/3 octave filter with crossover points of -3 dB, the Q-factor would have to be 4.3185

So I'm confused! Why did the max/msp example take such a low Q (high bandwidth)? Can someone confirm that the Q-factor of 4.3185 is the one I need?

(added for convenience: the patch from the examples section)