Guitar Amp Sim for Amp Players?

[guitarzan]

... In my world, the amp is the instrument and guitar is the controller...

Most definitely. Very few people thinks like this. I've always thought that the amp together with the guitar forms ONE instrument, and the other can't be excluded. The cable from the guitar to the amp is the 7th string so to speak. I've always wanted that the amp sims should include the warts and all from the real world amps. The thing with electric guitar in my world, is that - provided you have the right real amp and real settings - is that while you're playing you should be able to sound both NICE and clean and "linear" and with the split second movement of your pick attack you can sound UGLY, if you'd like. And of course, mostly in between. You should be able to get hideous out there sounds with the pick attack, and go totally mayhem...

Exactly! It seems to me amp simulations up to this point cut off exactly just short of the point I want to ride — that area between, where it's all up to the guitar volume pot and picking dynamics which way it all goes, ugly or nice.

I know amp sims are already valuable studio tools, but I want one I can actually play — and it has nothing to do with detailed modeling of anything, at least in my thinking. It's not that the behavior isn't exactly the same as some certain amp — it's a type of behavior missing altogether, completely absent, not there at all...gahhh, no one gets it that knows how to code...

[guitarzan]

Zen-Drive Pedal Boutique in Acustica Nebula form. Amps are another area.
Ultimate Guitar Mega Pack Collection .
We only have to look at the advancements in visual technology, like CGI and animations. Hopefully, with more powerful computers and advancements in software, more realistic amp sims will become available.

I will definitely check those out, but I'm almost sure my old computer won't handle it. I think I'm going to go ahead and update, get a new DAW going again. I was always hopeful of the tech behind Nebula... made it seem like everything was going to be possible.

[mystran]

I don't know if you'd want to model all of these (never mind other things in the signal path). Of course, you'd have to model the interaction of the amp setup with the incredibly microphonic Firebird pickup too.

One thing to keep in mind is that when you start considering the tricks that involve the guitar itself in an acoustic feedback loop, you really need to start worrying about the loop latency and if the original technique involves standing 1 meter from the amp, then realistically you simply can't put AD/DA converters in the loop and expect it to work and this kind of stuff really is impossible to fake properly in a simulation, unless you also simulate the guitar itself.

[guitarzan]

One thing to keep in mind is that when you start considering the tricks that involve the guitar itself in an acoustic feedback loop, you really need to start worrying about the loop latency and if the original technique involves standing 1 meter from the amp, then realistically you simply can't put AD/DA converters in the loop and expect it to work and this kind of stuff really is impossible to fake properly in a simulation, unless you also simulate the guitar itself.

What about a special guitar interface that communicated directly with the sim? I read here at KVR about that new Trueno synth and that's had me thinking about digitally controlled analog hardware. It doesn't seem like it would necessarily have to be super high tech or expensive to build — maybe like boutique stompbox price?

EDIT: Feedback is no problem, I have a lot of different ways to get feedback at any volume.

[guitarzan]

OK, I got it, you're talking about feedback. Somehow puting "acoustic" in front if it threw me off.

I can get feedback even at headphone levels, I have a Fernandes guitar with the Sustainer, and also an old style Sustainiac, the one that'll clamp onto any headstock. I want to try one of those FreqOut pedals — I read those basically work the same way as a feedback eliminator except boosting the sensed feedback frequencies rather than cutting them. I also want to build a monitor using a flat panel and surface drivers (aka: bone shaker, panel driver, surface transducer), that might work well — plus it could be covered in tweed grill cloth!

Using the Sustainiac or Sustainer isn't exactly the same as real feedback, even with an attenuated tube amp — the saturation just doesn't build up the same, the signal isn't really recycling through the amp the same way. It works though.

Maybe if there were a special amp interface it could serve as a FreqOut (or Sustainiac) and get the feedback swell right too? Jfet or tube pre-amp... plus hopefully drive the modeled power amp and speaker behavior in a more dynamic way by providing the sim more information. Someone out there has the resources, maybe team up a boutique pedal builder with an amp sim developer while we're dreaming big.

Ha! If we threw it all in a box it could be called a "guitar amplifier".

My latest invention: The Wheel!

[The Noodlist]

A new one to me
https://klevgrand.se/products/stark
Next months Computer Magazine is offering a free version, no doubt with cut down features.

[The Noodlist]

STARK – Amp Simulator
https://www.youtube.com/watch?v=rhPyprwhGjY

[guitarzan]

I don't really hear any power-amp in there, but it's got extra crispy cleans and crunch. I didn't notice any nasty noise spikes or anything, either. Probably a twang monster!

[guitarzan]

Maybe it's time to try rewording my original question.

In some amps, mainly vintage tweed-era, when the power amp starts to clip a few things happen that are not really simulated completely or at all in current amp sims (IMO).

Power amp behavior that isn't currently simulated completely (IMHO):

The output transformer saturates (? Brick Wall Limiting, tame the high end?)

The rails "give" (voltage sag)

I then believe (all personal theory from here on) the power-amp, starved of voltage, begins to behave as a Voltage Controled Amp (VCA)

The voltage fluctuation then acts as an Envelope Generator (sag - as experienced by the guitar player)

Voltage sag also causes the power-amp slew rate to start doing some seriously AFU Wave Shaping — truncated triangle-like and saw-like waveforms, compounded by sag

The net effect is that the guitar signal seems to never go flat squarewave against the rails, it actually feels like it's bucked off the rails - the more it's pushed, the harder it bucks — plus towards the extreme you get this wild raw analog synth-like wave shaping and triggered amplitude envelopes.

The most exagerated and easy to hear example (not necessary suggesting modeling this amp) is Neil Young on his Live Rust album. Cortez the Killer is the peak power-amp overdrive event — listen for those amplitude envelopes and the crazy wave shaping. The song immediately preceding Cortez is Powderfinger, and there you can gain additional insight by hearing Neil heat up the amp (and it's a great song — I can't listen to either tune in isolation, for me Powderfinger then Cortez, always).

So it's not detailed modeling I'm asking about, but more like simulated general behavior in a realistic way (close enough for rock 'n' roll standard applies).

In your opinions, can these behaviors be simulated in a general way using well established audio processes like Brick Wall Limiting, Wave Shaping, Envelope Generator (or Envelope Follower)/VCA — all this probably happening in Parallel Gain Stages (I think may be necessary to sound more "organic"), or any others I haven't thought of…

Can it be done? All ideas welcome!

[Mats Eriksson]

This with the power amp behaviour is an elusive thing to model. The main culrpit or problem with modelling is they're trying to make something totally chaotic, random, unlinear.... linear. They try to calculate and "read-ahead" chaos and take a guess what is supposed to happen.

I download the STARK amp simulator shown above. Demo. While it has lots of treble and twang...I'll come to that in a moment...it doesn't behave that well when turning down the volume of the guitar, and compare it to say some of the amps insid S-Gear. Speaking of twang, which seems Starks better traits, when you connect a Tele to it it lacks that power tube "zzzzzzzz" that is only heard when you crank the power amp. The "Brad Paisley" sound if you like. Not that he's alone on it but Tele into a cranked Vox AC30. When cranked (no crunch or mild distortion) there's a sizzle and buzz going on underneath the tone, that is velvey shimmery. The multi-layered levels of tone, one more compressed than the other and the verge of different kinds of clipping even produce square wave notes. I try to find demos on YT of it but have failed. I hear it on SOME studio tunes by Brad. Now, not that country or Brad's my stuff... but as someone pointed us to STARK amp sim. I like their layout for sure.

The "flyback" current and interplay occuring between speakers and power amp are yet to be simulated properly. When you tax a real amp to beyond safety levels. I am very well versed in Neil Youngs live sound on "Rust" especially on those two tunes. It is too many stochastic things going on at the same time... I know very well what you mean. But the thing is, is it THAT sought after except of you and me...like "I know of only God and one more, that would like that in a sim, but I've forgotten his name..." sort of thing.

[The Noodlist]

Gotta agree with the single coils, mine (Tone Rider Pure Vintage) sound great through a Laney LC30II, but rather lacking and thin through amp sims.

[JCJR]

Depending on the nature of the speaker, you might even get some "power sag" effects due to speaker coil resistance change because of voice coil heating.

Different speakers would have different heating and cooling time constants depending on design.

Driven by a clean solid state amp (which is not typically real picky about output load impedance except that power = rms volts ^ 2 / impedance) voice coil heating might be mostly clean power compression.

But a tube/transformer coupling might do funnier interactive things as temp modulates speaker impedance?

[guitarzan]

This with the power amp behaviour is an elusive thing to model. The main culrpit or problem with modelling is they're trying to make something totally chaotic, random, unlinear.... linear. They try to calculate and "read-ahead" chaos and take a guess what is supposed to happen.

I firmly believe in the close-enough-for-rock'n'roll standard. Seems like it would be easier to just generate similar randomness for some things. I'm not sure yet if this example applies to power-amp simulation at all, but Destroyfx had this really cool and simple effect called dfx Skidder (looks to be still available — open source no less!) that was basically just an advanced tremolo that let you dial in as much randomness on different parameters as you wanted, and it was amazing to me how much life just a touch of "random" can add. I can just imagine that having several instances running through parallel gain stages would be awesome, even if they were set at almost subliminal effect levels. It would still sound natural, but more fluid and 3d, not like an "effect" at all... maybe. I intend to set up a computer to fart around with this stuff again. Maybe even resurrect the old P4 Precision if I can find my ancient but quite low latency IEEE 1394 audio interface, just so I can use energyXT again.

The "flyback" current and interplay occuring between speakers and power amp are yet to be simulated properly. When you tax a real amp to beyond safety levels. I am very well versed in Neil Youngs live sound on "Rust" especially on those two tunes. It is too many stochastic things going on at the same time... I know very well what you mean. But the thing is, is it THAT sought after except of you and me...like "I know of only God and one more, that would like that in a sim, but I've forgotten his name..." sort of thing.

Depending on the nature of the speaker, you might even get some "power sag" effects due to speaker coil resistance change because of voice coil heating.

Different speakers would have different heating and cooling time constants depending on design.

Driven by a clean solid state amp (which is not typically real picky about output load impedance except that power = rms volts ^ 2 / impedance) voice coil heating might be mostly clean power compression.

But a tube/transformer coupling might do funnier interactive things as temp modulates speaker impedance?

Again, stuff like flyback current and motional impedance and other behaviors are mostly ignored now, so how bad could it be to "subtly" fake it somehow? Motional impedance is usually just vaguely described as something like a random enforcement or cancelling of certain frequencies, almost like nearly nothing is known about it (though I did once find reference to a white paper from the '70s about the subject) — hell, creatively utilized Skidder-type randomizer thing to the rescue! And as minor as something like that might seem, Ted Weber thought that representing motional impedance was the key to realistic speaker simulation, so it seems like it should be given at least some attempt.

Less subtle would be the wave shaping and "envelope generator" type behaviors, at least when taken beyond a certain point. Here again, I think parallel gain stages with varying levels of the simulated behavior would sound more "natural", less overtly like an effect, even if the simulation is on the crude side.

Neil Young is just the best example I can think of to hear power-amp overdrive because it is extreme. I do think a lot if people would enjoy that type of experience if it could be contained in a sim, even if incompletely, but the same type of behaviors dialed back would benefit all styles, IMO, experienced as improved "feel".

I am just hoping that there are ways to improve amp sim feel right now using regular old audio processing. Worth a try, anyway. Of course, it would be much, much better if someone who actually knew what they were doing would give priority to feel and dynamics in amp simulations.

[cturner]

...but Destroyfx had this really cool and simple effect called dfx Skidder (looks to be still available — open source no less!) that was basically just an advanced tremolo...

ICYMI, Audiority’s Tube Modulator and Goodhertz TremControl. Even Soundtoys Tremolator.

[JCJR]

Depending on the nature of the speaker, you might even get some "power sag" effects due to speaker coil resistance change because of voice coil heating.

Different speakers would have different heating and cooling time constants depending on design.

Driven by a clean solid state amp (which is not typically real picky about output load impedance except that power = rms volts ^ 2 / impedance) voice coil heating might be mostly clean power compression.

But a tube/transformer coupling might do funnier interactive things as temp modulates speaker impedance?

Again, stuff like flyback current and motional impedance and other behaviors are mostly ignored now, so how bad could it be to "subtly" fake it somehow? Motional impedance is usually just vaguely described as something like a random enforcement or cancelling of certain frequencies, almost like nearly nothing is known about it (though I did once find reference to a white paper from the '70s about the subject) — hell, creatively utilized Skidder-type randomizer thing to the rescue! And as minor as something like that might seem, Ted Weber thought that representing motional impedance was the key to realistic speaker simulation, so it seems like it should be given at least some attempt.

Tis hard to say. There is so much BS written about anything "audiophile". Difficult to even identify all the BS. Hell for all I know everyting I say is BS.

Googling "speaker power compression" among several hits which seem "reasonable" is this one: https://www.linkedin.com/pulse/power-co ... der-wilson

Maybe some of it is right but some also seems wrong. He describes a scenario where after 10 seconds of heating, speaker coil resistance has changed from 5.5 to 7.5 Ohms, and he proceeds to declare that this is the same as 35 Percent Distortion! Well for one thing the impedance isn't exactly the same as coil resistance.

Even a true impedance change from 5.5 to 7.5 ohms, driven by a typical clean low impedance transistor amp, would only cause a loss of about -1.35 dB. If it takes 10 seconds attack (and presumably at least that much release) then maybe we would measure negligable increase of THD or Intermodulation Distortion. Just some "fairly clean" modest compression?

The resistance needs to change (fairly drastically) at audio rates before we might expect much thermal-caused intermodulation distortion. That would be the same as letting too much ripple get into a Compressor side chain because of too-short attack and release times.

There are so many speakers out there. Some of the nicest ones for guitar (like "vintage" Webers and vintage Celestions and Jensens and CTS) were intentionally built cheap. Crappy speakers sound great on guitar. Maybe some of the crappy speakers really can significantly heat and cool at audio rates? Maybe there is a way to test it.

I liked Ted Weber. Dunno what "motional" impedance is. Is that necessarily related to voice coil heating, or some other effect in the electro-magnetic-mechanical system?

Hifi nuts could get righteously worried about thermal impedance changes (even if too slow to cause intermodulation distortion) in multi-driver speakers with passive crossovers. VC heating could mess up the crossover alignment. About half the power gets dumped into a passive crossover. If the crossover inductors also significantly heat then that might be another source of drift.

However those kind of dynamic "phase cancellation" "frequency balance" worries might be less likely on single-speaker guitar systems? Just wild guessing. Maybe it would be possible to test a tube/transformer amp's frequency response driving different impedance speaker loads. Just putting various size power resistors in series with a guitar speaker might be useful for testing tube amp load-impedance-vs-frequency-response? Or maybe not. Dunno how fancy that a valid test would need to be.