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On Tue, Mar 19, 2013 at 5:57 PM, Fons Adriaensen wrote:
> On Tue, Mar 19, 2013 at 05:26:27PM -0500, Charles Z Henry wrote:
I was replying to Tim's comment on putting two filters in series--I guess
if you've settled on Q=0.5 then it's fine. I thought you were discussing
this in general.
> In this case we don't want overshoot so Q must be <= 0.5.
Okay--I misunderstood the application. The lowpass filter is definitely
better handling all the possible inputs.
If it was always a fixed time over which you need to fade in, I think you
could find a good analytical function to use, or make a table that always
has a predictable effect.
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On Tue, Mar 19, 2013 at 5:57 PM, Fons Adriaensen =
Mar 19, 2013 at 05:26:27PM -0500, Charles Z Henry wrote:
> You guys are splitting hairs... kind of misses the forest for the tree=
The same thing as what ?I was re=
plying to Tim's comment on putting two filters in series--I guess if yo=
u've settled on Q=3D0.5 then it's fine.=A0 I thought you were discu=
ssing this in general.
In this case we don't want overshoot so Q must be <=3D 0.5.
The form I posted actually has a little bit of feedback,
so Q is jusst above 0.5. This makes it reach its target
value in finite time, bit still with an overhsoot of less
than 1/1000 dB. The same code can do any Q value you want,
just use the righr value for the feedabck term (a).
> The best way to avoid "zipper noise" is not to create it in =
'Slow enough' might be too slow. A fader should still 'fe=
it has no delay.
> I think you should figure out a different shape of ramp that doesn'=
That is precisely what a second order lowpass is doing.
Raised cosine, indeed better than a linear ramp.
Ideally you'd want the higher derivatives to be continuous
as well. A raised hyperbolic tangent will do that, or at least
come close to the ideal in finite time.
The problem with all thoe programmed ramps is that they require
extra logic to handle the case where the requested gain changes
during the ramp. A linear filter solves that problem neatly with
much less code. And in fact *any* system that handles that case
well will be a low pass filter is some disguise.<=
div>Okay--I misunderstood the application.=A0 The lowpass filter=
is definitely better handling all the possible inputs.
it was always a fixed time over which you need to fade in, I think you=20
could find a good analytical function to use, or make a table that always h=
as a predictable effect.=A0Chuck=