Although I have heard that CD players are on average better at reproducing sound, I have also heard that the best sound quality can still be had from high end phonographs. To what extent is this true?
The digitization process does introduce some distortions into the sound signal, including aliasing (confusion about high frequencies) and quantization error (round-off errors in recording the softest sounds). However, these distortions should be so small or at such high frequencies that they should be inaudible. Still, there are always some audiophiles who can hear (or claim to hear) these imperfections.