[music-dsp] Blurps and Chirps when changing filter parameters

Didier Dambrin didid at skynet.be
Thu May 7 15:28:30 EDT 2009


Talking about exponential ramping, what do you think of stacking exponential 
ramps to produce a more natural curve (one that doesn't start too abruptly)? 
(that's the way I smooth up my compressor's gain envelope)

Are there other better known ramping methods? Exluding the ones that produce 
values out of [source,destination] range, that is.



>
> You need to interpolate the coefficients in real time to remove the 
> 'zipper
> noise' you get when changing filter parameters rapidly.
>
> There are a number of approaches, the simplest o which is exponential
> ramping, so each time you ramp your coeffs you'd do..
>
> b0 = ( b0_target - b0) * ramp_factor
>
> where b0 is the coeff you use in the audio processing & b0_target is the
> output of your coefficient calculator. ramp_factor is typicaly a small
> number & would be related to how quick you want the coefficient to settle.
>
> You can also interpolate linearly which produces a more natural sweep imo,
> so each time you ramp..
>
> b0 = b0 + (b0_target - b0_last)*ramp_factor
>
> Ramping every other sample is ideal, any artifacts will be at Nyquist (or 
> so
> i was told by a learned colleague ;)
>
> Regards
> Rob
>
> 


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