True Circuit Modeling (non-impulse-based) plug-ins

General Discussion about Guitar Amp modelers
wallyaudio
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True Circuit Modeling (non-impulse-based) plug-ins

Postby wallyaudio » Wed Dec 28, 2016 12:29 am

Some time ago I decided to stop using samples in my musical productions and exclusively use virtual instruments that model the circuits and the results have been amazing. I want to do the same with the effects and not use anything based on impulse responses (convolution) but unfortunately the information about it is very poor. Apparently we have a lot of information here about guitar amp emulators but the most important thing which is hidden by most developers remains a mystery. Could we all put together a list to clarify the subject? I leave here an incomplete tentative list to start with:

AcmeBarGig - ?
Fractal Audio Systems - ?
Ignite Amps - ?
IK Amplitube - Circuit Modeling?
LePou Plugins - ?
Line6 - Circuit Modeling?
NI Guitar Rig - Circuit Modeling?
Overloud TH1/TH2/TH3 - Circuit Modeling?
Peavey ReValver - Circuit Modeling?
Positive grid - IR/Convolution?
Softube - IR/Convolution?
Studio Devil - Circuit Modeling?
TSE Plugins - ?
Waves GTR - Circuit Modeling?

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PVDHP
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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby PVDHP » Wed Dec 28, 2016 3:05 pm

Where have you seen a distortion modeling involving impuse response? There is a lot of ways of implementing distortion but not with impulse responses. IRs are being used AFTER the moment signal gets distorted to make it sound like it was feed to a cabinet and captured via mic.

DaveClark
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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby DaveClark » Thu Jan 05, 2017 6:19 pm

wallyaudio,

If you're really serious about committing to true circuit modelling, then your only real option is to use a circuit simulator such as SPICE for the electrical portion. For the mechanical portion (speaker + cabinet) you may want to look at COMSOL Multiphysics. You won't be able to render anything in real time or even close to it. If you are rendering in real time, then you are not doing what you are claiming you are doing.

Regards,
Dave Clark

wallyaudio
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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby wallyaudio » Sun Jan 08, 2017 10:15 pm

Well, it seems that my question has not been understood. I am not referring only to products that model distortion but to all. I just want to know which ones are algorithmically modeled 100%, whether or not they include cabs or reverb.

As an example you can check out Magix Vandal...
http://www.soundonsound.com/reviews/magix-vandal
...and this interview with the developer.
https://www.youtube.com/watch?v=T6skNMTd8oU

DaveClark
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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby DaveClark » Mon Jan 09, 2017 5:27 pm

wallyaudio,

It seems that you didn't understand my answer:

No audio software developers are doing what you describe in your own choice of Subject ("True Circuit Modeling"). True circuit modelling is done by EE's using SPICE and other circuit simulators that step through circuit behavior in small time steps, usually resulting in non-realtime results.

Furthermore:

You seem to be confounding "True Circuit Modeling" with "algorithmic." The term "algorithmic" is often used in reverb modelling to mean nearly the opposite of true physical modelling --- a shortcut that too often results in nonphysical and inconsistent acoustic behavior. Using impulse responses is more akin to true physical modeling than algorithmic reverbs, especially if you solve the acoustic wave equation to obtain them.

I understood your question perfectly well and am just pointing out that it is based on serious misperceptions. There isn't any reason to attempt to provide answers to questions that presume the opposite of reality.

Regards,
Dave Clark

SnuggleKittens
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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby SnuggleKittens » Fri Jan 13, 2017 11:10 pm

That is not quite true DaveClark 8) .

The plugins i made are pure circuit models. I make them from the schematic of the amps and thats it. No wave shaping, just a state space circuit model and a non-linear tube model.

The catch is that they are very cpu heavy, but with modern CPU's you can run about 4 instances in real time.

unfortunately some people have trouble running them (might be the C++ redistributable dependency)

You can find them here.

viewtopic.php?f=51&t=21819

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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby DaveClark » Wed Jan 18, 2017 2:01 am

Hi SnuggleKittens,

Although I applaud your efforts, I have some serious concerns about your claims:

1) I see from the thread you referenced that they don't work for those who posted about their experiences.

2) From Norton, I see that there are "many indications" that the file isn't trustworthy. Norton removed the two very small, even tiny dll's without even asking me anything.

3) You posted that you skip the tonestacks in some cases, and that these are pre-amp only --- no power amp, no phase-splitter, etc. You're also skipping the speaker and cab, admittedly an electromechanical system rather than purely electrical, but there is a non-resistive load after all. The circuits you are modelling are quite incomplete by the standards of "True Circuit Modeling" of a guitar amp as described by the OP.

4) You mention a nonlinear tube model, but you didn't describe how it works. This is where the problem becomes severe. As you should know, the usual approach in SPICE is to use an iterative solver with time steps that may need to become very small, especially when the gain is turned way up in my own experience. With four stages of gain in a pre-amp and several tubes in the power amp, and solving ALL of the equations simultaneously (not processing one stage at a time), this would normally take more than realtime. If you're not solving all of the equations simultaneously, then of course you may do better than realtime, but you certainly would not be solving the actual circuit; you would be solving something along the lines of a sequence of buffered circuits, for example.

5) You didn't provide any information whatsoever about comparisons of accuracy and performance to SPICE or any other circuit simulator. All you provided is the dll's and an audio clip. To test what you are doing, it would be necessary to compare signals at internal nodes, among other things. You should know perfectly well that you cannot just say, "Wow! This sounds really good, so I must be truly simulating this circuit very accurately!"

In short, you have not shown to me that you have done "True Circuit Modeling" of a guitar amp, so I stand by my post.

On the other hand, if you actually have figured out how to model a complete four-stage pre-amp plus power amp with some non-resistive load and achieved SPICE-level accuracy, and can run four instances at 88.2 Ksamples/second, you will definitely be some sort of real guitar hero very soon. No doubt we all wish that this were true.

Regards,
Dave Clark

SnuggleKittens
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Re: True Circuit Modeling (non-impulse-based) plug-ins

Postby SnuggleKittens » Wed Jan 18, 2017 12:50 pm

Hi again DaveClark

1) They work for me on two different machines (thats all i have to test them on at the moment). I get the feeling that maybe the people having problems are opposed to installing the C++ redistributable (which is fine) although i am not certain.

2) The dlls are tiny because its just the code. No GUI, no lookup tables, no other data. If i wanted to spread malicious code (if i even knew how to write such a thing) this would be an incredibly inefficient way to do it.

3) I can easily add tone stacks to any of my models, in fact the IIC+ model has the tone stack. I mainly made these for my own personal use, and i prefer without the tonestacks. I just wanted to make them available in case anyone found them useful.

Also there are no standards of "true circuit modelling" except your own. It just depends on what you require. The sims are "true circuit models" of preamp sections. Maybe someone else says it's not "true circuit modelling" until you model the coal fired powerstation generating the power that runs the amp (at least here in Australia :o ) Personally i like to play through my laptop and run the sims into a real poweramp thus i don't really want any power section simulation.

It is true that at this stage my high gain models (with a lot of preamp tubes) couldn't handle the inclusion of the power amp and transformer etc. But in a few years if CPU power increases this will be possible (and maybe some people are already doing it). It's probably possible now for amps with fewer tubes. Maybe if i get some time in the future i will try.

4) The problem is not as severe as you think. As far as the state space model goes, the capacitors are discretised and integrated via the trapezoidal rule. The timestep is naturally the sampling rate (in this case 88.1kHz since they run at 44.1KHz but are oversampled 2x). The tube model is this one by Dempwolf and Zolzer http://recherche.ircam.fr/pub/dafx11/Papers/76_e.pdf and is solved in real time (yes simultaneously) using Newton's method.

The problem with SPICE comparisons is that the SPICE solution is only as good as the tube model used in the SPICE simulation. You could implement the same tube model in SPICE but to be honest i can't be bothered / don't have the time. As far as the rest of the circuit components go, i have tested the frequency domain performance thoroughly and compared it to spice. The solutions are very very close over the entire spectrum.

5) Finally, accuracy is an interesting point. Accuracy with respect to what? components in real amps have tolerances of up to 20%. All individual tubes are also slightly different, voltages coming in from mains vary from outlet to outlet. I know from experience that two of the same model of amp can sound quite different. I guess you could painstakingly measure a single specimen and try to recreate that exact amp, but that kind of goes against my entire goal of simulating the circuits just from the schematics.

I feel the definition of accuracy for amp sims should be as follows: you are unable to say for certain whether the sound was produced by "some" instance of the real amp or by a simulation targeting the same amp model.

If that is not the case then that doesn't say much about any of the current commercial amp sims available. Most of the same amp models sound significantly different from product to product. This would imply that either: one is correct and any that sound different are inaccurate, or they are all inaccurate. Really at the end of the day, if an amp sim sounds good to you, then use it :cheers:.

Snuggles.


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