[sdiy] Linear/Log FM (was "Living VCOs" PCB in 2009 ?)

[Yves Usson]

OK on second thought I think I see what the problem is, the linear  
modulation
is a linear frequency modulation but it's extent is depending on the  
current
circulating in the servo circuit thus if one changes the CV at the V/ 
OCt input
one changes the linear modulation amplitude and therefore a constant  
offset applied to this input
will not be constant in frequency offset since it also depends on  
what is on the V/OCT input.

Gee that was puzzling !

Yves

Le 10 déc. 08 à 12:42, Tom Wiltshire a écrit :

>
> On 10 Dec 2008, at 11:19, Simon Brouwer wrote:
>
>> "Linear" on that type of modulation input means that the frequency
>> deviation has a linear relation to the modulation voltage. *This  
>> deviation
>> is proportional to the unmodulated frequency*.
>>
>> In contrast, Jürgens "linear detuning" control provides an  
>> independent
>> frequency offset.
>>
>> So with the linear modulation input (if it is not AC coupled!), or  
>> with
>> the normal fine tuning control, you could get a frequency  
>> deviation of
>> e.g. 1 Hz but this deviation would be 2 Hz that when you play a  
>> note one
>> octave higher.
>>
>> With the "linear detuning" you could set a 1 Hz deviation across  
>> the pitch
>> range. This way you can get a pleasant rate of beating between  
>> VCO's at
>> lower notes without them sounding too out of tune at higher notes.
>
> Is this right? That wasn't my understanding of a FM linear  
> modulation input. I thought the folllowing;
>
> If it's linear, a signal of a given level produces a modulation of  
> a given depth, say 200Hz. What this represents musically will vary  
> with pitch.
> If it's logarithmic, a signal of a given level produces a  
> modulation of a given interval, say 2 semitones.
>
> So a linear detune control is just a small DC offset fed to a  
> linear FM input.
>
> Or am I hopelessly wrong about this (like lots of other stuff)?
> Thanks,
> Tom
>
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