There are some DA converters that use interpolation:

http://en.wikipedia.org/wiki/Interpolation

"In the mathematical subfield of numerical analysis, interpolation is a method of constructing new data points from a discrete set of known data points."

So these interpolating, upsampling DA converters add the missing info, so they claim. Here is a good article on Simaudio Moon CD players, and why they use oversampling, not upsampling:

http://www.simaudio.com/upsampling.htm

"In fact, and most probably, these latest methods actually deteriorate sound quality if the conversion takes the sampling rate to a frequency that is not a direct integer multiple of the original sampling rate, being 44.1 kHz for audio CD."

A while ago I was wondering if converting from 44.1 to 48 would cause any quality loss, because this is done all the time for DVD-videos. Someone films a show and then they need taper's rig audio to synch to it, cause camera mic audio sucks. So they find a 48 > 44.1 FLAC or SHN set, then upsample to 48. I did some listening tests (on PC speakers) between:

1)44.1 FLAC set

2)44.1 FLAC set > upsample to 48 in Soundforge at highest quality settings w/anti-alias filter.

#2 sounded duller in comparison to #1. I liked #1 better.