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

[Tom Wiltshire]

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