Doepfer

> > We use white noise as audio input signal and max. resonance
> setting at the
> > A-127. Then the filters are adjusted by ear.
>
> Ah, interesting. I'm still having difficulty understanding how
> this means you can reference the frequency range to an absolute
> set of values, but it has given me a couple of things to try!
>
> Thanks,
> Tim

The exact measuring procedure is a bit more complex for filters that do not
have available self-oscillation. You need a measurement equipment that gives
you the frequency response of the filter and how it changes with the control
voltage (combination of a frequency modulated sine wave over the audio range
as audio signal and an envelope follower at the filter output which gives
you the filter response curve). But if you use a noise signal and set the
filter's resonance to it's maximum (and use the bandpass output - if
available) you will hear kind of a "pitched noise". If you want to adjust
the filter CV input to 1V/octave a difference of one Volt of the CV has to
correspond to a pitch change of one octave. This parameter is adjusted with
the trimming potentiometer for the scale. After that the absolute frequency
of the filter is adjusted to the desired value (i.e. the frequency if all CV
inputs are zero Volt and the manual control is fully CCW). For this the
trimming potentiometer for the frequency offset is used.

Hope this helps

Dieter Doepfer