Originally Posted by Ruined
Second, there is sampling rate. This is in reference to your "48khz" above. The common sampling rates used these days are 44.1KHz, 48KHz, 88.2khz, and 96KHz. The higher the sampling rate, the higher the frequency range reproduced. If you divide the sampling rate in half, you get the frequency response range. So, a CD which uses 44.1khz sampling rate has a frequency response up to 22khz. A DVD which uses 48khz sampling rate has a frequency response up to 24khz. And, an HD DVD which uses a 96khz sampling rate has a frequency response up to 48khz. But here is the kicker - humans can only hear up to around 18-19khz maximum and most speakers only reproduce up to 20-21khz. Therefore, it is pretty much accepted that sampling rates higher than 48KHz are pretty much a waste since we can't hear those frequencies and most speakers can't reproduce them anyway. Another reason why high sampling rate formats like DVDAUDIO failed.
Well, it really depends on the audio. The purpose behind 192khz audio for example, is to ensure that you are going to properly capture most of the crests and valleys of each soundwave. For 48khz to truly reproduce the original sound, (or at least, capture a sound wave that could reproduce the original via sinusoidal interpolation) you would have to work under the assumption that the frequency doesn't change much. For something like opera music (which is what most people consider to be the most pure,) 48khz just fine. But other types of music (e.g. rock, metal) you'll benefit from a higher sample rate. Though admittedly, you probably aren't going to notice a difference with the typical sub $1,000 sound setup that most people have at home.
Super Audio CD (different than DVDA) does the best job at digitally reproducing a proper sound wave, and if you have a proper sound system, you will notice the difference.