[Timo]

Originally Posted by hatembr

and is this an audible effect ?
btw, what is nyquist ???

Nyquist is the minimum digital recording frequency that is needed to capture a signal (to a minimal degree).

If you imagine a sine wave at 20KHz. - In order to capture that signal correctly digitally, you will need a mimimum recording frequency of 40KHz to capture it so you can be sure of including both the positive and negative rise and fall of a single cycle of the sine wave - otherwise the sine wave will be distorted and create phasing effects and other aliasing artefacts as the digital binary representation of a sine wave at a greater frequency would be impossible to reconstruct.

But to be honest when you get towards the top end of the Nyquist frequency aliasing still creates artefacts anyway, as pure sine waves are turned into triangle waves or much worse. The digital representation of a sine wave at its Nyquist frequency is not a faithful sine wave, but much more a distorted one, like a simple "on/off" waveform as opposed to smooth curves (although post-filtering helps at the Digital-to-Analogue stage).

The human hearing goes up to 20KHz+ . Therefore "CD quality" was designed to capture up to at least that frequency, so to do that they needed to record the signals at at least twice that frequency in order to capture and play back a 20KHz signal correctly. They eventually used 44.1KHz, which can play back frequencies up to 22KHz. But 44.1KHz is still effectively the minimum they can get away with. Higher representations are better, as they make the frequencies at 20KHz even more faithful (instead of being turned into triangle/saw/pulse waves), regardless of the fact we can't hear further than 22KHz+.