In your vid 'Interpolation Sampler Channels & Aliasing' as you refer to the "Nyquist limit" while speaking a graphic appears which reads "Nyquist frequency". Was the difference intended?
It's the same thing, just used both terms so people who use one or the other would recognise their favourite
Nyquist limit = sample-rate/2
Essentially when the frequencies contained in an audio source exceed exactly 1/2 the sample rate, then 'aliasing' occurs. The frequencies above 1/2 the sample rate actually fold back down in to the audio spectrum, with the fold-down position depending on how far above the limit they are. You can see that happening in my sweep example.
You will notice the CD standard sample rate of 44.1 kHz has a Nyquist limit of 22.5 kHz, 2.5 kHz above the theoretical upper frequency limit of human hearing. The extra 2.5 kHz was infact some room for roll-off filtering I believe in the A/D (sampling) stage so they were sure not to miss the 20 kHz information.
In all practical experience however most people struggle to hear above 18 kHz and there really isn't much musically of interest above 15k Hz.