[sdiy] ... Simulating a Moog

[Julian Bunn]

Hi Peter,

> john mahoney wrote:
> 
> > It occurred to me that, given the circuit diagrams for e.g. 
> a Moog, and a
> > lot of free time, one could enter everything into Spice and 
> completely
> > simulate the behaviour of the instrument. With the results 
> you could make a
> > faithful digital reproduction of the Moog. And you'd never 
> need to touch a
> > soldering iron J
> 
> 
> >From my experience working for a speaker company that used 
> it a lot in
> engineering, Spice at best simulates and is better for determining
> parametric ranges than acoustic properties.
> 
> Then, what happens when certain older than sin parts have no 
> Spice model?
> It then goes into the 'create life' as the first process step 
> kind of deal

I think you'd have to look for equivalents, or in the worst case
develop your own simulation of each. I doubt there is a Spice model
for the SG3402 ring modulator chip used in the Minisonic, but this
chip behaves in a very easily modelled way. A lot of work though,
nonetheless.

> 
> But let's say one pulled it off, then everything you want to 
> control it with
> would also have to be within the spice realm  And assuming 
> you got those
> other circuits successfully replicated as well, for the $$ 
> you'd have to
> shell for a computer powerful enough to handle the size of 
> the now 'patched'
> spice model for the standard synth VCO into LP into VCA 
> oldie,  you could of
> hired a team of solderists to do the work for you!

The hope would be to come up with a parameterization of each
module's output based on its input. This would just be a matter of
fitting the input and output curves with a polynomial, for example. Once
you have the transfer function for each module in this way, you can discard
SPice and just solve any given module configuration analytically
very fast ... in real time on a decent desktop I guess.

> 
> Plus, it's sort already been done with DSP anyway in regard 
> to the Moog:
> 
> http://www.moogmusic.com/detail.php?main_product_id=90
> 
> does it sound anything like the real deal?  Nah....but it's 
> fun.  Notice
> their official description eludes to this:  "Software 
> Synthesizer BASED on
> the classic Moog Modular Synthesizer. "
> 
> - P
> 

That looks like a fun product! I wonder how they did it, and if
it doesn't sound like a real Moog, where did they cut corners or
go wrong?

Julian