2nd-order allpass VCFs?

Martin Czech martin.czech at intermetall.de
Tue Nov 23 09:29:37 CET 1999


:::For the "parallel-bandpass filters subtracted from input signal"
:::technique to produce really nice notches, I have the feeling that you
:::would need filters that can achieve fairly LOW values of Q, as lower Q
:::values in the allpass filters tend to produce more prominent sounding
:::notches. The state-variable filter I programmed in Csound has problems
:::with values of Q that are less than 1, but I will give this a try with
:::this filter and other bandpass filters when I have time (which may not
:::be until the next millenium, in all honesty). Anyone here experimented
:::with this, especially with low-Q bandpass filters?  Also, would a global
:::feedback path work to accenuate the effect, as it does with cascaded
:::2nd-order allpass filters?
:::
:::Thanks,

I took a look at low Q state vars on my homepage. At Q=0.5 The poles
meet (real) , for lower values they spread (also real).

m.c.

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