[sdiy] Resonator type filters

[Ian Fritz]

Just to be sure we are all together on this, a string filter bank needs 
high enough Q's to give something around 10-12dB peak-to-valley ratios. 
And a common adjacent channel frequency ratio may be taken as the fifth 
root of 2.1, following the original Matthews/Kohut/Burhans research. 
Note that octave repeating frequencies would be a disaster! If anyone 
knows of a graphic EQ that can do this, I would love to hear about it. 
My personal take on a string filter is described in Electronotes EN#107 
(1979). It was built a couple of years earlier. It has 36 resonanators 
in banks of six, with adjustable amplitude for each frequency and 
adjustable Q for each bank.

Ian


On 6/29/2017 2:44 PM, Richie Burnett wrote:
> The Q factor of each filter is obviously higher for something like a 30 
> band graphic EQ where the bands are 1/3rd octave spaced, than for 
> something like a 10 band EQ with 1 oct wide bands.  As you've said the Q 
> factors aren't particularly high though in a typical graphic EQ.  In 
> fact I don't think they are even fixed in low-cost GEQs, because i've 
> seen much more expensive GEQs that are specifically marketed as 
> "constant Q" and are supposedly superior.
> 
> If you want to simulate body resonances of musical instruments the 
> graphic EQ probably isn't the most precise tool to use, and may even 
> fall well short in terms of the required Q factor.  I've never tried, 
> but it's quite a coarse tool.  I have tried using graphic EQs to correct 
> for nasty room modes over the years, and it doesn't work very well.  In 
> both cases I suspect that a decent multi-band parametric EQ would be 
> much more precise and better suited to the job.  Room modes at bass 
> frequencies tend to have quite high Q-factors and are very narrowband, 
> so they demand very narrow notches from an equaliser, if room 
> equalisation is your thing.  A graphic EQ is nowhere near precise enough 
> in my experience, at least for small home studios.
> 
ijfritz.byethost4.com