Re: [Audacity-nyquist] hp filter was Problem with this plug-in...

[Sami J. <sam...@gm...>]

Hi,

I think it relates to the delaying nature of the process. What's
"inside" the filter when the filtering begins? Is it garbage? I think
not. How do we define the initial condition? In real (analogue) life
we practically never face this kind of situation, because the filters
just have been on and work forever. Anyway, hard to say what the
"ripple" means without seeing it. But let's assume this:

The audio has offset so that it's heavily on the positive side. How
does the filter see the beginning of the audio file? It sees a jump
from zero level to highly positive level, like a step. Smoothing out
the step takes time, determined by the cutoff frequency of the filter.
During that time the resulting DC level "crawls" towards zero. Test
it. Create a moment of silence in the middle of this kind of audio,
HP-filter the audio and see if the effect is the same as you see in
the beginning.

Also, crossed my mind that high-order filter algorithms can "bounce".
If we need low delay and steep cutoff, I think that's an obvious side
effect.

Sami


On 29/11/05, David R. Sky <dav...@sh...> wrote:
> Hi Sami,
>
> the problem Edgar was speaking about when applying a highpass filter was
> the initial 50 milliseconds of 'ripple' or something, which I can hear
> after repeated application of the rectifier plug (I have to rely on
> sighted people's feedback about this since I can't see the screen to
> check). Do you know what that initial ripple is and how to remove it
> without further distortion? Or how to at least reduce it?
>
> David