25 Aug
2013
25 Aug
'13
6:52 p.m.
Hi, thanks for the software!
I'm using Lorenz as a modulation source, but it appears that amplitude
decreases greatly as I slow down the rate. Is there a high pass / DC
blocking filter somewhere in there?
Here's my code, in Supercollider:
{SinOsc.ar(freq: 100 * (2 ** LADSPA.ar(1,1774,0.01,1,1,0,100)))}.play
thanks again,
Mark Hadman
On 25 August 2013 01:00, Tim Goetze <tim(a)quitte.de> wrote:
[Fons Adriaensen]
On Sun, Aug 25, 2013 at 12:21:52AM +0200, Tim
Goetze wrote:
I think the question deciding the quality of the filter fade is, how
big will the phase difference between the two filters be? Amplitude
differences shouldn't matter when we crossfade, as long as we're not
phase-canceling.
These are very simple filters that don't take long to settle on a
stable phase relationship. A reasonably small parameter change will
not change their phase response by much, so my expectation is that
there will be only little cancellation and the fade thus close to
imperceptible; at most a slight attenuation of high-frequency content.
Just theorising over a glass of wine though.
I'm planning to evade this problem by
crossfading between two parallel
static filters. Some phase mismatch issues can probably be expected
when the parameter sweep covers a larger range, but I'm hopeful it
will turn out not to be much of a problem in actual practice, and that
we will find out soon. It really needs a fix.
I doubt very much if that will provide a practiacal solution.
The state of the filter depends on signal history. Depending
on the parameters, this could be quite long. The simple solution is to smooth the input
parameters,
limiting their rate of change. Nobody expects an EQ
section to change from 100 Hz to 10 kHz in less than
half a second (unless it's a synth VCF module, but then
you definitely need something else than a biquad).
Yes, that is a very convenient way to solve it, perhaps the preferable
one given the realities.
Tim
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