Does audio upsampling create noise/artifacts or degrade the signal? I've read that upsampling performed in digital music playback can color the sound, produce artifacts, etc.  For example, an audio file ripped from a CD might be 44.1Khz/16-bit, and then upconverted to 48Khz/16-bit and played via an optical digital audio output.  Audiophiles say this is bad because the signal needs to be "bit perfect" to be reproduced correctly.    

Is this correct?  My vague knowledge of DSP from grad school leads me to think that all upsampling should do is increase the bandwidth of the signal.  But, since the source signal is bandlimited, there shouldn't be anything new in the added bandwidth.  And I don't see why the process would color the sound.

What am I missing?
The up-sampling process will always change the signal in some measurable way. However, if it's done properly the changes are negligible and don't result it any audible difference. Most commercially sample rate converters (hardware or software implementations), do a really good job at this.

Off course, if done badly, upsampling can result in clearly audible signal degradation. I'm not familiar with Apple's implementation but I would assume that they got this correctly.