The speed I'm talking about is not the speed of electricity traveling from the positive supply down through the tube/transistor and into the circuit ground.
That is the vertical axis which is responsible for providing an instantaneous voltage (potential) that represent the instantaneous air pressure.
One the other hand, the horizontal axis represents the time domain.
If for some reason the vertical motion of a rise in voltage (increase in pressure) fails to make it to the theoretical peak of the sine wave then we see this as compression. If you place the compressed image over the ideal image - it can be seen the somewhere (maybe 3/4 of the way up) the amplifier trace begins to fall behind the ideal trace. It's velocity has slowed down. This means that a portion of the sine wave has been altered, its shape is no longer ideal and now represents the shape of a lower frequency. Likewise if the amplifier trace is seen as reaching a higher than ideal voltage then its velocity has increased. This looks like expansion (or the opposite of compression). That portion of the amplifier's wave now appears to be a higher frequency. The pitch has changed.
This is classic Doppler.
By securing the velocity along the time domain - it forces the amplifier to put out a trace that would superimpose onto the ideal trace. The shape of the sine wave is not altered and will always represent the fundamental frequency. Harmonics of the locked sine wave are non existent.
Distortion and linearity are inversely proportional. The less the linearity the more distortion. Instead of trying to make a linear amplifier, I made one that does not distort. If you have zero distortion - you automatically have 100% linearity. (same as air).
In the absence of Doppler distortion, every instrument in a full orchestra can be heard separately as if you were at the original venue.
Yes electricity travels at roughly the speed of light.
The horizontal movement of a signal representing a sound wave through a circuit has a specific playback speed.
If you record sound at Mach One you must play it back at Mach One.
Roger