[sdiy] simple "level separator"?

[Scott Bernardi]

Just connecting a the FET gate control to a comparator would mean that the
FET would switch on and off on each cycle, even when you were above the
threshhold (because the waveform will go below the threshhold during each
cycle). In a noise gate, you are actually comparing the input >amplitude< to
the threshhold, and that requires some sort of averaging (i.e., filtering),
and that is where your delay/time constants come in. You can minimize the
delay through various techniques, but then you get away from a "simple"
circuit - an engineering tradeoff. For example, see this envelope follower
circuit based on an Electronotes design:
http://home.attbi.com/~sbernardi/elec/og2/og2_envfollower.html

VINTVOLT wrote:

> Hi,
> I'm in need of a simple circuit that would be used to separate high and
> low
> levels from a signal. It's transfer function should be like this:
>
>     ^out
>     |         /
>     |        /
>     |       /1:1
>     |      |
>     |      |
>     |      |
> sym  ======---------->in
>           thr
>
> where the threshold should be adjustable, so very similar to a noise
> gate,
> but without any time constants. It should be instantaneous.
> I searched the web, but could not find any simple circit. I thought
> about
> using a fet in the audio-path with the gate connected to the output of a
> comparator. would that work?
>
> --
> Carles Vila Deutschbein
> Departament d'Acústica -Engingeria La Salle