31 Aug
2014
31 Aug
'14
9:42 p.m.
On Sun, Aug 31, 2014 at 08:13:01PM +0100, W.Boeke wrote:
Sorry Fons, if you google "moog filter
schematic" you will
see 3 stages, where a stage is a capacitor in series with 2
transistor emitters (which have a diode V/I characteristic).
All versions I've every seen have four stages, and with three
the feedback wouldn't have the right phase. If you find a
schematic with three stages please post a link.
Each stage is a capacitor in parallel with the series connection
of two emitter impedances, and driven by a current source, the
collector currents of the previous stage.
About that complicated code: I saw implentations with
a lot of
code lines, and preventing oscillations originating from the
non-linear tanh functions needed a lot of care.
I analysed this thing to dead around ten years ago, when I wrote
the MCP plugins. There is no instability problem resulting from
the non-linearity. The main problem with a straightforward digital
implementation is that it becomes a bad approximation at higher
frequencies, this requires some attention to get right. The easy
solution is to run it at a higher sample rate.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)