I'm not imagining it, it does exist, it's basic transmission line theory.
Try connecting your scope to a signal generator, with a 50
hm: output impedance running at just 5MHz, via a 10m long twisted and the pulses won't look very square, you'll notice a lot of ringing. Now repeat the same experiment using the same length of 50
hm: coaxial cable, the ringing will be greatly reduced. This is because it's acting as a transmission line at the harmonic frequencies, before with the twisted pair which has an impedance of 600
hm:you were getting standing waves and transmission line resonance but this has all disappeared with the 50
hm: cable because it's matched to the source.
Now normally this isn't a problem for audio, this is because the length of the cable is short compared to the wavelengh but this isn't the case with the example I used in my previous post as the cable is so long it needs to be considered as a transmission line. If I wanted to run a cable to distribute audio from my home in Bedford to you in Derbyshire, stepping up the voltage wouldn't be good enough, I'd need to match the impedance too, if I wanted to keep the ringing and standing waves at bay. As I have illustrated previously, in practise this would mean increasing the voltage anyway as practical transmission lines have a higher impedance than most speakers.