On Fri, 02 Dec 2016 18:50:27 +0100
Jörn Eichler <joerneichler@xxxxxxx> wrote:
I noticed, that a high q value "whistle" sound created using Analog BPF2 and
SV 1BPF filters on white noise, both set to the same frequency, differ a lot.
SV
1BPF sounds almost a minor sixth lower than Analog BPF2.
I looked at the code to see, if the freq passed on to the filters differed.
It
does not. However, I found an interesting difference in how the two filters
use
the freq they get:
Analog BPF2 does this (file AnalogFilter.cpp line 189):
omega = TWOPI * freq / synth->samplerate_f;
while SV 1BPF does this (file SVFilter.cpp line 69):
par.f = freq / synth->samplerate_f * 4.0f;
Note the different factors (2*PI for Analog, 4 for SV).
Two notes with frequencies f1=4*f0 and f2=2*PI*f0 differ by 783 cents, which
is
almost a minor sixth and also pretty much matches the frequency difference my
phone app showed for some tests.
Is this behavior of SV 1BPF intended?
Should the tooltip window account for this difference and simply show the
"effective" frequency SVFilter seems to use instead of what it is actually
passed?
