# [PD] overdriven speaker

Martin Schied crinimal at gmx.net
Fri Oct 22 04:43:20 CEST 2010

```  On 22.10.2010 03:10, Mathieu Bouchard wrote:
> On Fri, 22 Oct 2010, Martin Schied wrote:
>
>> yeah, but this is often the case when messing things up in pd. I
>> tried rpole~ 1 with sinewaves first which worked as integrator, but
>> already had different results for the output of rpole~ if the wave
>> started at 0 or pi/2 (which is logic, but I didn't think about it
>> first...)
>
> um, yeah, the amount of DC is rather relative to where you start
> looking, and where you stop (or where you're at so far). That's why I
> used things like [rpole~ 0.99] to force it to recentre around 0 rather
> quickly.
>
I wanted to use a fairly high a < 1 because then the phase for all
frequencies is approximately 90° off like for the ideal a=1. Using
slightly smaller factors and comparing input / output didn't satisfy my
expectations. maybe that would't matter at all - let's experiment...
>>         lop's gain compensation = 1 - 0.999 = 0.001
>>         rpole's gain to compensate for = 1/0.001 = 1000
>>         cutoff frequency = 0.001*44100/2π = 7.019
>>         therefore use [lop~ 7.019] with [*~ 1000] (in any order)
>> I thought about lop~ doing similar things too, but didn't know what
>> lop~ is doing and I'm sure I wouldn't have figured it out in any
>> reasonable time this morning. thanks!
>
> Ah, I also think that you'll like to know that the total weight of an
> input sample in [rpole~ a] can be written like this :
>
>   k = a^0 + a^1 + a^2 + a^3 + a^4 + ...
> but
>   a*k =     a^1 + a^2 + a^3 + a^4 + ...
> therefore
>   k-a*k = a^0 = 1
>   k*(1-a) = 1
>   k = 1/(1-a) is how the gain of [rpole~] is computed above.
that's indeed interesting. So the gain is defined for a constant signal
having the same input and output samples (or in other words DC having no
amplification) if I understood it correctly.

> I attached my [lop2~] abstraction, which is a rpole~-version of
> [lop~], with a signal-rate right-inlet. I posted it some time ago.
I remember it now, and already saved it in my mail archives :)

cheers
Martin
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