[music-dsp] Comb filter freq response

[David Lowenfels]

Hi Conor,
   AFAIK you are correct in your understanding about the poles of the  
comb filter.
The reason why some guitar notes are more resonant than others, is  
that the filter response is static, while the notes you play are  
variable.
You will have more resonance when you play a note that is "in tune"  
with the filter.

> float L = Samplerate()/fInput;

this is not quite correct. fInput should be fCombTune or whatever you  
want to call it. It has nothing to do with the frequency of input  
(guitar), unless you are doing fundamental pitch tracking or  
something to make a dynamic filter.

The length in samples of your delay line in the comb filter, L,  
determines the period of the filter tuning...

L samples / samplerate = Tcomb
1 / Tcomb = fComb
therefore fComb = samplerate / L
that's what you had, but you confused yourself calling it fInput

Cheers,
-David

On Dec 16, 2006, at 6:44 AM, Conor J Curran wrote:

>
> I am baffled because when I play a guitar through this external some
> notes are far more resonant than others. I don't understand this, I
> thought the pole/resonant is constant therefore its resultant effect
> would be constant throughout the notes on the fret board of a guitar.
> Pretty new to DSP design so this might seem like a dumb question.
>
> best regards,
> Conor