<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>2.1^.2 was first used by Ralph Burhans, IIRC, for his clavier resonator. He found this to give the fewest overlaps of harmonics of different notes.</div><div><br></div><div>A few months ago I ported my old 36-stage analog bank into Reaktor and added a variable spread parameter to experiment with. It can have a uniform spread, or random numbers can be folded in for a less regular one. String resonators to formant filters and beyond. The things we can do!</div><div><br></div><div>Ian</div><div><br>On May 8, 2019, at 6:55 PM, Dave Leith <<a href="mailto:dave.leith@gmail.com">dave.leith@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div><div dir="ltr">Check out the frequencies of the Serge Resonant Filter. Intentionally does not use doubling of frequencies.<br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, May 8, 2019 at 5:24 PM Ben Bradley <<a href="mailto:ben.pi.bradley@gmail.com">ben.pi.bradley@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">"Frequencies every half-octave around 1000 Hz (LP at 88, 125, 177,<br>
250, 354, 500, 707, 1000, 1414, 2000, 2828, 4000, 5657, HP at 8000<br>
Hz)"<br>
<br>
I spend a few minutes thinking about this, and what you'll have<br>
musically is when a note "hits a frequency" of a filter, not only will<br>
a fundamental be emphasized, but also its even and multiple of 3<br>
harmonics as well. Other notes would have one or a very few harmonics<br>
emphasized. I'm not sure how this would sound, but it did seem<br>
somewhat lopsided.<br>
<br>
I had read the previous discussions on filter banks and comb<br>
filtering* and discovered at least one tidbit I didn't notice or had<br>
forgotten. Several references use the formula 5th root of 2.1 (or in<br>
this case you might use square root of 2.1, or to place them closer,<br>
square root of 1.9) for the frequency ratios, so octave and other<br>
harmonics of one filter frequency don't necessarily fall into other<br>
filters.<br>
<br>
For a one-off design, for the experimentation and development that you<br>
appear to be doing, I'd want trimpots for frequency and/or Q, to be<br>
able to more easily tweak things and hear how the sound changes. This<br>
could help to determine if 1 percent capacitors is really worth it, or<br>
even audible. I'd want to hear the difference, but I'd offhand guess<br>
that 5 percent is good enough.<br>
<br>
* Perhaps not a "good" name for this, since the comb filtering I'd<br>
seen refers to dips in response caused by adding a phase-shifted or<br>
time-delayed signal to the original, but it's also been used for fixed<br>
filter banks.<br>
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