Filter Frequency Modulation

[Theo]

----- Original Message -----
From: Daniel Gendreau <gendreau at rochester.rr.com>
To: Rob Rickner <rrickner at zoo.uvm.edu>; Synth_Diy
<synth-diy at node12b53.a2000.nl>
Sent: Saturday, April 01, 2000 11:18 PM
Subject: RE: Filter Frequency Modulation


> Method #2: (aka. Auto Wah)
> Another andio control method extracts the volume envelope from the audio.
> This usually involves rectifying(full or 1/2 wave) the audio signal and
> using a diode/capacitor to give a 0 attack / fixed(controlled by a pot)
> decay rate. It is very similar to an AC voltage regulator from a power
> supply. From there, you low pass filter the envelope (to take out the
> jaggies) and probably do an expo conversion.
>
> Hope that helps,
> -Dan G.
>


Rectifying audio with a diode mostly doesn't work.
Depending on type diode you use it need about 1/2V before it starts to
conduct.

A fast rectifyer (that starts right at 0V) will do the trick.
These are normaly build around a opamp and two diodes.
Let me know it you need an example.

Hope this helps,

cheers Theo.