[sdiy] Analog Modeling, with a computer!

[Antti Huovilainen]

On Wed, 14 Sep 2005, Jeff Farr wrote:

> Ok, so I have a secret... The whole reason I'm learning how to make
> electronic instruments is beacuse I wish to understand the concepts used to
> make component modeled VA synths akin to Arturia's product line. Now, I am

http://dafx04.na.infn.it/WebProc/Proc/P_061.pdf (shameless plug)
AFAIK, that is the only published paper about modelling actual circuits in 
analog synths.

There are two possible ways to go about modelling a particular synth 
circuits (say a filter): You can measure the response, tuning etc of the 
circuit and try to tweak your digital model to fit that or you can start 
from the schematic and derive a model based on that. Most people do the 
first while I much favor the latter.

> in my discussions with those at Yamaha, Wine County and a few others the
> conversation comes to a complete halt when I ask about how their analog
> modelling works. Not even a "compass pointer" on where to look in order to
> teach myself. So far, in a year or searching I have found nothing about

That is due to two reasons: first, there aren't really any publications on 
the topic (excepting the one I pointed before) and they cheat and do not 
actually model the circuits (and wish people to believe their lies^H^H^H^H 
marketing).

> SDIY? does anybody have a light they can shine on the type of algo needed to
> act like a tl072, 3080, elko cap? I've begun looking into SPICE, as it

This is a mistake "newbies" often make. Modelling individual components 
does not make sense. Instead you need to identify the relevant 
non-idealities and model the whole circuit such that it matches those. A 
capacitor alone does not do anything. However once you connect two 
resistors and diodes to the capacitor, you have an AD envelope generator 
and can model that (typically modelling attack and decay stages 
separately).

I have some free circuit modelling VST plugins online at
http://antti.smartelectronix.com

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova