Physical Modelling from a circuit schematic

[DavenH]

How does one go about developing a software model of an electronic circuit?

Here's a list of schematics for audio hardware (mostly amplifiers).

Clearly one needs to understand the schematic language, let's assume that's not a problem.

For example, if the circuit were an effect, there'd be an input, plenty of resistors, inductors, capacitors etc, but it's unclear to me how these components could be emulated with software.

Help would be appreciated, thanks

[antti]

How does one go about developing a software model of an electronic circuit?

Get a degree in EE and/or dsp, spend a few years studying musical circuits and some more getting a good understanding of musical dsp. Then one can start.

[AdmiralQuality]

Nobody actually does it this way, despite what some companies' marketing hype would have you believe.

That's because it would be wasteful. A lot of any analog electronic intrument or amp is there to do stuff that is essentially "free" in the digital realm.

The reverse also applies. A tube amp gets its sound mostly from the response characteristics of the tubes. (OK, and the output transformer, and the speaker and cabinet... but I'm simplifying to make a point.) On the circuit diagram that tube is just one component. But if you're modelling a tube amp you're going to put a lot more attention into duplicating the tube's behavior (and notice how I didn't say "simulating".) Indeed, your REAL world tube amp is going to sound very different, just by changing the types of tubes you use in it. So even the individual components themselves have a lot of potential for variety, and that stuff isn't described in the schematics anywhere.

Still, someday, when we have more CPU power to waste, there should be some interesting possibilities along these lines. But for now, it would be wasteful in a realm where we all want to save as much CPU power as possible.

[AdmiralQuality]

Furthermore, and copyright violation issues aside (that site states "information deserves to be free"... well if it was, all the people who DESIGNED those circuits wouldn't have been able to feed their kids!)

Anyway... here's an example...

http://www.freeinfosociety.com/electron ... php?id=617

The "Inductor" here in this Vox Wah is probably referring to the famous Fasel inductor. Which has particular properties that aren't specified anywhere in the schematic (guage of wire... number of windings... etc, etc) So it's not like any of these instruments, effects, and amps can be recreated just from the information on these schematics. They're more useful for repair of the actual device. You'd be hard pressed to even build a REAL one without at least more info on what the actual components were. And to model them in software you'd need to know that AND have some serious data sheets on the component's performance characteristics.

You're trivializing something that's VERY hard here (and indeed, a bottomless pit of subjectivity). If you want to make software instruments and effects, don't start with the analog schematics (though it doesn't hurt to keep that stuff in mind as it can provides clues as to the behaviours you're trying to emulate. But remember it's emulation, NOT simulation.)

[AdmiralQuality]

Another example... the famous Tube Screamer TS808 (some say the secret to Stevie Ray Vaughan's tone... that and a Fender Super Reverb amp)

http://www.freeinfosociety.com/electron ... hp?id=1136

See those components labelled JRC4558D? Nobody makes them anymore. This is why these particular old pedals are reselling for way more than they originally sold for. They do make new ones, but everyone says they're not as good as the ones with the original chips.

And what do they do? The schematic doesn't specify! They're just black boxes.

These schematics are only useful if you have the actual, real, parts, or reasonable substitutes. They're good for repair. Making modifications. And those who want to build their own pedals and amps and have a pile of parts avaliable.

[DavenH]

Well antti, I was hoping for a slightly more timely solution, and costly... but point taken.
Will a degree in computer science and proper motivation suffice?

AdmiralQuality, thanks for your helpful posts. I can't begin without ignorance, so sorry if I seem to be 'trivializing' what may be impractical. I guess the fact that it's a challenge for NI says something... still, I'd like to know more about it.

About copyright, do software firms get licenses to emulate patented hardware?

[AdmiralQuality]

Oooooooooooh! A telephone ring modulator! I'm gonna use this to disguise my voice next time I arrange a kidnapping!

http://www.freeinfosociety.com/electron ... hp?id=1233

There's a nice weapons section on this site too. http://www.freeinfosociety.com/electron ... php?cat=11

Coilgun
EMP
HERF
Jacob's Ladder
Magnetic Gun
Mini EMP
Model Rocket Launcher
Nausea Generator
Pain Field Generator
Pocket-Sized Pain Field Generator
Solid State Tesla Coil
Stun Gloves
Stun Gun
Stun Gun 2
Stun Gun 3
Tesla Coil
Tesla Coil 2
Vortex Cannon



lets hope nobody models any of those in software!

[AdmiralQuality]

Well antti, I was hoping for a slightly more timely solution, and costly... but point taken.
Will a degree in computer science and proper motivation suffice?

AdmiralQuality, thanks for your helpful posts. I can't begin without ignorance, so sorry if I seem to be 'trivializing' what may be impractical. I guess the fact that it's a challenge for NI says something... still, I'd like to know more about it.

About copyright, do software firms get licenses to emulate patented hardware?

Don't confuse patent and copyright and trademarks. They're all different things.

Patent is like if you invent the light bulb. Nobody can make lightbulbs for a certain period of time without your permission. But you have to apply for that patent.

Copyright is your inherent ownership of any intellectual property you create (including software and analog circuit designs.) You automatically have copyright of anything you created originally. Same as for art and music. But you can't copyright an idea. (See the recent Da Vinci code failed lawsuit.) Nor can you copyright something short and trivial, like the name of a book or a movie. Except...

Trademarks are why I can't go out and make a VSTi that looks like a Jupiter 8. Roland will sick vicious lawyers on me and claim to own the colors black and orange. And why I can't rip off their logo or make a clever pun based on the name of their synths. But even though you can't copyright a name, you CAN make the name of your book or movie a trademark. But like patent, you have to go to the trouble of registering it and proving that you have reasonable right to claim it for your own.

But yes, definitely some software companies have worked out deals with original manufacturers to duplicate their designs (or at least layout) and steal their looks and even names. Arturia are the kings of this, though I'm sure NI did it on their FM7 and some other things as well.

Fun site! But yes, a LOT of copyright violation there. That's why the political "justification" on the home page and info about famous hackers, anarchy cookbook... lotsa bad stuff. The NSA probably has my IP address just cuz I opened the weapons page.

And, seriously, I mentioned copyright not because that would stop you from making your own software fuzz pedal. Again, we don't actually copy the circuits when modelling something in software so there's no copyright violation. But, as someone who makes a living (or attempts to) from software development, I'm pretty sensitive to the fact that that site is giving away other companies' intellectual property, and claiming they have some kind of god given right to do it. It's tantamount to cracking or reverse compiling someone else's software (and you can imaging how that kind of thing goes over on this board!)... so just for karma's sake, I mention that it's BAD. Still... lotta fun and thanks for the link.

[antti]

And what do they do? The schematic doesn't specify! They're just black boxes.

And inside that black box is a relatively low noise opamp which does not suffer from phase reversal when the inputs exceed allowed range - in other words, an opamp you can use for hard clipping in non-inverting configuration. Nothing magic, it just happens that most other _common_ audio opamps won't work there due to the phase reversal issue.

Did I mention the "several years studying musical circuits" part yet?

[AdmiralQuality]

antti!!!!

So as you see, this stuff IS knowable... but it's a lifetime pursuit. I only know enough to know how LITTLE I know. But that was my point... this stuff is HARD and those schematics don't contain the answers. They're repair manuals, and not much more.

[DavenH]

And what do they do? The schematic doesn't specify! They're just black boxes.

Did I mention the "several years studying musical circuits" part yet?

Is there some internet resource with which to begin this holy study?

Or should I consider some pertinent electives this fall?

[AdmiralQuality]

I was gonna ask if you were going to Waterloo.

You know what? I went to FILM SCHOOL. I'm self taught. So I can't really advise you on the proper academic course to take. But yes, learn C++ (DON'T waste TOO MUCH time with Java or... god forbid... C#.. even though that's great stuff for getting a job... it probably won't be a job programming music software) and learn as much DSP as you have access to.

Aside from that, you're in the right place already. The information you'll get on this board is probably WAY better than you'll get from most classes. Get a C++ compiler, download the VST SDK, and make a simple delay or ring modulator... that'll get you started. Then start asking specific questions on this board and watch the fur fly as all us "experts" compete to prove who's the smartest. It's like Tom Sawyer white washing the fence... you really can get others to do it for you.

[DavenH]

I need more time! Dammit... how can you work full time, sound design, compose, read Dune series, and write plugins and still get 4 hours' sleep?

[AdmiralQuality]

Well, I'm almost 40. So, you have LOTS of time... if you don't want it all to happen tomorrow. (And really, if it was THAT easy, then what would the value in any of it be? HARD is GOOD. But do be sure you really WANT it before you begin your journey, cuz you'll need that to get you through it ... not that it ever ends.)

Cheers, and good-luck.

[Karbon L. Forms]

I was gonna ask if you were going to Waterloo.

You know what? I went to FILM SCHOOL. I'm self taught. So I can't really advise you on the proper academic course to take. But yes, learn C++ (DON'T waste TOO MUCH time with Java or... god forbid... C#.. even though that's great stuff for getting a job... it probably won't be a job programming music software) and learn as much DSP as you have access to.

Aside from that, you're in the right place already. The information you'll get on this board is probably WAY better than you'll get from most classes. Get a C++ compiler, download the VST SDK, and make a simple delay or ring modulator... that'll get you started. Then start asking specific questions on this board and watch the fur fly as all us "experts" compete to prove who's the smartest. It's like Tom Sawyer white washing the fence... you really can get others to do it for you.

Yup. First thing I did when I dropped out during final year was go learn C++. 1 year later I'm getting paid to write music software.