[music-dsp] Modelling analog circuits at the component level

Ross Bencina rossb-lists at audiomulch.com
Thu Jul 8 01:25:50 EDT 2010

Hi Thomas

Yes, this is being done. Both in the research community and in commercial 
products such as those from UA (you can read their online blog for some 
understandable discussions). There are a few people on this list who do this 
kind of thing. I'm just an interested onlooker.

My impression is that usually the implementation techniques to do this stuff 
in real time involve a combination of real-time simulation of differential 
equations for specific components, IIR filters for "linear" elements, 
combined with "sampling" of static nonlinearities using lookup tables when 
this is appropriate -- these lookup tables can be renderd using off-line 
circuit simulators such as Qucs (qucs.sourceforge.net).

There have been some publications evaluating real-time simulation of 
components for musical use, for example:

Sorry, I don't have a bibliography of this stuff handy, someone else can 
probably give you some better pointers. Check out DAFX conference 
proceedings for example. I notice this is out now:

Special issue on virtual analog audio effects and musical instruments in 
IEEE Transactions on Audio, Speech and Language Processing (published in the 
May 2010 issue).

The guys at Helsinki University of Technology have published some research 
in this area also.

I think achieving your dream might require a system which can automatically 
evaluate the psychoacoustic effect of certain optimisations.



----- Original Message ----- 
From: "Thomas Strathmann" <thomas at pdp7.org>
To: "A discussion list for music-related DSP" <music-dsp at music.columbia.edu>
Sent: Thursday, July 08, 2010 2:46 AM
Subject: [music-dsp] Modelling analog circuits at the component level

> Hi!
> I have been thinking about creating routines that simulate analog circuits 
> like filters, waveshapers, overdrive, fuzz, chorus etc. at the component 
> level to recreate the non-linear and time varying behaviour of real 
> transistors, op amps, diodes, and passive components. Is this feasible for 
> realtime DSP on a modern processor at all, something like a 
> specialized/simplified version of SPICE taking arbitrary input values and 
> yielding the response of the simulated circuit? Where can I find papers or 
> other resources about approaches like these? I know that you can calculate 
> the transfer function from a given circuit and approximate non-linear 
> behaviour, but my dream is a piece of software that takes netlists 
> including the relevant parameters of the components used and functions as 
> a realtime audio processor ideally with the ability to affect some 
> disturbance like raising the ambient temperature.
> Thomas
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