24 Oct
2002
24 Oct
'02
6:05 a.m.
On Thu, Oct 24, 2002 at 01:50:29 +0200, Tim Goetze wrote:
ah, now i dig it. maybe you could make a note about
the intended
use in the valve doc?
Yeah, I should probably do that. Documentation (well english in general!)
is not my strong point.
good. do you think the 44100/12 oscillation is a
speaker
or output transformer effect?
I'm 90% sure its from the crossover between the two halves of the class B
amp (thats the power amp IIRC).
now i've seen your code i know where a good deal
of
what i have called aliasing is from. :)
Er, yeah. <shuffles feet>
did you mean to start the sample loop at index 1 in
crossover_dist_1404.xml? 0 sounds much better. i'm
I blame fortran. ;)
afraid it still aliases a little, but it does look
like it's basically doing the right thing iiutc.
I didn't think the aliasing would be audible. It uses a linear interp to
go from the bulk of the sub lobe to the true zero corssing, but that should
be OK. You do have smoothing set to 1.0 right? Otherwise it does something
crazy (fix for that later).
the problem with both the valve and the xover i think
is that the further you drive them, the edgier the
discontinuity gets. it would have to be computed at
There definatly shouldn't be a discontinuity. If there is then its a bug.
Also, the crossover effect is not amplitude dependent, maybe it should be,
but the way it was described to me it isn't. Another thing to mention here
is that many people claim the crossover effect isn't a desirable feature of
amps.
I think the valve needs to be applied gently (looking at the scope traces
from yesterday its a fairly mild effect), and then some harder clipping
needs to kick in.
my reasoning is that the problem we are facing here
is the same as in the generation of band-limited
square (or sawtooth, if you will) oscillation.
Yes, but if the aliasing isn't too bad though it can probably just be
solved with a bit of oversampling, 4x or 8x should be enough, though the
CPU use wil go up 4x or 8x. The basic valve should be optimised.
I can reduce the cost if I move the curve from e^-x to 2^-x with a fudge
factor, but does anyone know how this will effect the sound? Its not too
much work, maybe I should just try it.
- Steve