Are "Dynamic Bias shifting" and "Harmonic Movement" only myths ?

[Vivek]

Do these dragons really exist ?

Can you hear them ?

Do you immediately know which Amp in a mix is exhibiting Dynamic Bias shifting and Harmonic movement ?

Could you please post YouTube clips of best examples of Amps exhibiting Dynamic Bias shifting and Harmonic movement ? Thanks!

[teemuk]

Do these dragons really exist ?

Yes. These are phenomenons that have been recognised, widely documented, studied and exploited at least since the 1970's. Great deal of signal processors include such effects - probably for a good reason.

Can you hear them ?

Yes. I can hear a difference between amps/effects that introduce such dynamic effects vs. amps/effects that do not. Given though that the difference is so subtle that it is more evident in A/B comparison and when you know what to listen. It's probably not as distinct in a band mix.
I can also "feel" such differences since the dynamic circuit... well... reacts differently to picking and interacts with picking dynamics.

Do you immediately know which Amp in a mix is exhibiting Dynamic Bias shifting and Harmonic movement ?

Not neccessarily. Audible difference might be evident, not neccessarily what causes it.

Could you please post YouTube clips of best examples of Amps exhibiting Dynamic Bias shifting and Harmonic movement ?

Youtube search, for example, clips of Crate FlexWave series, Randall RG80/100ES, Carvin SX series, H&K amps, or Peavey TransTube amps. These employ bias and harmonic shifting. Better yet, listen to many tube amps like Trainwreck, Soldano, Rectifier, 5150 or Carvin Quad-X. Come to think of it, there are probably more guitar amps - tube and SS - that have such dynamics than ones that don't. With trained ear you can hear how the distortion's timbre changes in interaction with picking dynamics. It's easier to recognize in an A/B comparison though; in amp/effect sans dynamics you hear something missing and the distortion does not sound as "organic" (in lack of better description).

There's also a clip on Quilter Amps channel where they compare a Quilter amp to Marshall tube amp. The clip demonstrates the tone of bias shift leading to crossover distortion in good A/B comparison. It's definitely audible when you know what to listen.

Problem with many video clip examples is that they demonstrate amp tone vs. another amp tone, and you already hear a difference between them due to different responses. ...And it's much easier to notice a difference in frequency response than a difference in harmonics of distortion of a complex signal. Not too many clips demonstrating distortion w. dynamics vs. distortion without, and everything else being equal, I'm afraid.

Do note that the effects are subtle for ear but affect more "feel" and "touch response". IME, FlexWave amp clipping is evidently more organic and richer sounding than e.g. a Tube Screamer or an older Supersat Generation Peavey amp while the generic OD voicings methods share a lot in common.

[EBK]

I think of bias shifting and harmonic movement as being analogous to compression/expansion but in frequency content rather than amplitude.  I definitely can feel the "width" of the sound increase with asymmetry.

[Vivek]

I was in touch with the gentleman who wrote this

https://output.jsbin.com/zotaver

And incorporated into an online Amp Sim

https://mainline.i3s.unice.fr/AmpSim5/index.html

It supports dynamic transfer functions.

[Steben]

Definitely no myths.

There are a lot of other myths, but these are not it.

Remember not all bias shift leads to the same effect.
The drop of power supply (sag) causes the classic "divider fixed bias" in power amps to become dynamic as well. this can introduce cross-over distortion.
Cathode biased amps (no divider) usually have less power sag because they are usually "less" class B (meaning: they draw more constant current), but they have cathode shift which leads to compression and cross-over distortion in their own way.
And both of these effect are not the same as bias shift with duty cycle stuff going on in preamp tubes, which does not lead to compression or cross over.

The power amp stuff leads to spoungy character (compression) and somewhat less tight hairy muffled chords (cross over). This typical for the classic rock era in which volume roll off use around amp break up can create timbres of the tone without too much change in amplitude / RMS power.
The preamp stuff leads to shifting harmonic content which can bring changing aggressive patterns with pick attack etc. It is easy to see the latter is a "modern sound" element.

Cathode bias paradise for example Tweed Deluxe