[sdiy] Log and Lin Controls in a DIY synth - Where to use?

[jure zitnik]

disclaimer: everything i'll write is purely by common sense. i might
be wrong with something and the terminology is probably completely
whacked since english isn't my first language.

i don't think you'd like A, D and R controls logarithmic - logarithmic
means that the function value grows faster at higher input values - in
practice - if you had logarithmic attack it would mean that the
resulting time difference between 0% and 50% of attack setting would
be MUCH smaller than between 50% and 100%. it would make setting
longer attacks accurately much more difficult than shorter ones.
however it might just be what you're looking for. maybe you care about
precise setting of short attacks and not for long ones.

i hope i helped. i'm not 100% sure about VCAs being typically linear
but my common sense says so. the deal with tone pitch as percieved by
human ear is that with higher frequencies you need bigger frequency
differences to *hear* the difference (in pitch).

but that's not the case with amplification of audio signal versus the
perception of loudness - in fact it's the opposite. with louder sounds
you need to change the amplitude (amplification) LESS to notice the
same relative difference in loudness than with lower amplitudes.
that's why audio mixers have non-linear channel volume but inverse
logarithmic sliders... which could ofcourse be normal logarithmic
sliders if used for attenuation instead of amplification...

but probably none of these subjects are new to this list and i'm
probably excersizing it only for myself :) i'm sure someone will
respond and write exactly what is the most common configuration.

cheers,
jure

On 2/3/06, Chris Manders <wight446 at yahoo.com> wrote:
> Hi all
>
> Thanks Jure and Yves for your replies.
>
> I am understanding this now. I was under the mistaken impression that VCAs
> only had Log inputs. I will be building a Linear VCA so won't need to fiddle
> about.
>
> One final question - In a basic ADSR circuit, I assume that the Sustain
> control would be Linear (to describe the voltage level at Sustain) but the
> other three controls are Rate controls and therefore would be Logarithmic.
> Is this correct?
>
> Thanks
> Chris
>
>
> jure zitnik <kokoon at gmail.com> wrote:
> i'd say linear for VCA. but log for anything pitch-related.
>
> most modulars have 2 separate inputs for VCO modulation - lin and log.
>
> jure
>
> On 2/2/06, Chris Manders wrote:
> > Hi folks
> >
> > I am going back to my old love, Synths after a brief absence.
> > About 6-7 years ago (seems like yesterday) I successfully built a Moog
> > ladder filter and a VCO using help from some of you guys out there.
> > I am going to start collecting up bits and bobs for continuing this
> project
> > of building my first Analog(ue) synth.
> >
> > This will probably be a real Newbie question to you guys out there, but in
> a
> > typical synth which Potentiometer controls should be Linear, and which
> > Logarithmic?
> >
> > I understand what Log and Lin are, and this may be something I just need
> to
> > get my head around to fully understand it.
> >
> > Am I right in saying that if a control describes a voltage level (CV to
> > Pitch being 1V/Octave), then that control should be Linear. All the rest
> > should be Log (as for example Amplitude being a Log scaling)?
> >
> > My head starts to ache when I think of other routings. If a Linear LFO
> level
> > control is set to sweep up and down by 1 Volt, when fed into the VCO it
> will
> > modulate the pitch up and down by an octave. Would this LFO signal then
> have
> > to be converted to a Log scaling if one wanted to feed it to the VCA for
> an
> > even tremolo effect?
> >
> > Thanks
> > Chris
> >
>
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