[sdiy] Resonator type filters

[Mike HEQX]

I see your point Rich. It's a waste of time to try to kludge a 31 band 
eq into something more. I'll try it on a junk eq I have laying around, 
just to see what might happen.

This paper looks like a good resource.

http://www.thatcorp.com/datashts/AES13-031_Digitally_Controllable_Audio_Filters.pdf


Mike


On 6/29/2017 4:44 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.
>
> In the graphic equaliser schematics that I have seen, I don't think 
> you can "tap into" the band filters in the way that you mean Mike.  
> They are usually wired such that they appear in the feed-forward / 
> feed-back path of an op-amp, so with the sliders set mid-way you get 
> neither gain boost nor gain cut.  I don't know off the top of my head 
> how you would make a voltage controlled analogue graphic equaliser 
> with VCAs.
>
> In the digital world it's done differently, and everything is just 
> coefficients in a big calculation, so you can automate centre 
> frequencies, Q factors, boost/cut amounts etc, for each band if you 
> wanted to.
>
> -Richie,
>
>
> -----Original Message----- From: Ian Fritz
> Sent: Thursday, June 29, 2017 7:11 PM
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Resonator type filters
>
> Yes, but I have never never seen one with the high resonance and the
> large number of stages needed for a string filter -- do you have some
> specific examples?  I would love to have a VST string filter but cannot
> find any.
>
> Ian
>
>
> On 6/29/2017 9:46 AM, Richie Burnett wrote:
>> A graphic equaliser (analogue or digital) is really just a bank of 30 
>> or so resonant filters.
>>
>> -Richie,
>>
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