[sdiy] Polymoog resonator question

[rburnett at richieburnett.co.uk]

On 2018-10-11 10:52, Mattias Rickardsson wrote:

> Generally speaking in a multi-band parametric eq or resonator like
> this I'd definitely want the ranges to overlap more or less - having
> 60-300 & 300-1500 & 1500-7500 without overlap sounds like a
> questionable idea from Moog's side - but on the other hand there can
> be some problems with huge amplitudes when peaks collide.

I don't think you will get really huge amplitudes when you tune two 
resonators to the same amplitude.  This is a parallel filter bank.  It's 
not like a parametric EQ where the audio is fed through each resonator 
one by one in series.

Parametric EQ:  Signal gets boosted by say 10dB in narrow range around 
f1.  Then, signal gets 10dB boosted in narrow range around f2.  Then 
signal gets 10dB boosted in narrow range around f3.  When f1=f2=f3 the 
gain in this frequency area is 30dB.

Moog parallel resonators:  Signal gets divided into three equal parts.  
Each part gets signal boosted by 10dB in a narrow range around f1, f2, 
or f3.  Then the three portions of the original signal get combined 
again.  If you split a signal into 3 parts, do the same thing to all 
three parts and then combine them back together, isn't it the same thing 
as applying the processing one to the whole signal?

There will be a gain increase in the second case but I don't think it 
will be anywhere near as profound as what you would get with a true 
parametric EQ when all bands are tuned to the same frequency and full 
boost applied.

Perhaps of more interest are the deep notches that you get *between* the 
peak frequencies of the resonators where the skirts of the responses 
meet each other with opposite phase, and annihilate each other!  Now 
that's what the phase inversion switch on the middle band is all about 
influencing...

-Richie,