Would someone explain what "up sampling" means and how it can affect the sound?

rockanroller,
upsampling is a digital domain process where the bit rate of the digital music stream is changed to something higher by an integer number. In redbook CD the bit rate of the music stream is 44.1KHz.
It appears to me that you are not versed in digital signal processing hence going into too many technical details is not advisable.
But, due to the 44.1KHz sampling rate of redbook CD, the analog filter at the output of the DAC needs to have a very steep filter skirt to attenuate the DAC clock energy. Well, making such a steep skirt analog filter has the major disadvantage that the in-band filter response (i.e. the response of the filter in 20Hz-20KHz audio region) attenuates the high frequency response of the music/program material + it creates a lot phase shift which destroys the integrity of the music signal.
One way around this is to upsample the music signal by an integer number, say, 2 to 88.2KHz. Now, the filter skirt of the analog filter following the DAC can be much less steep. This makes the analog filter easier to design, it adds less phase shift inside the 20Hz-20KHz audio band. So, from an analog filter design perspective this is a win.
What about the digital music bit-stream perspective? The way upsampling is done they zero-stuff. So, imagine your bit-stream was a 11111 at 44.1KHz & we want to upsample to 88.2KHz. then the new zero-stuffed bit stream would look like 1010101010. Now we can clock this new bit stream at 88.2KHz & the logic1s would be encountered at the same time as they were when we clocked the data at 44.1KHz. So, we have increased the bit rate. but we've destroyed the original data - our orig data at 44.1KHz had a string of 5 logic1s; the new 88.2KHz bit stream has alternating logic1 & logic0. what's up with that? You are correct if you asked this question. So, here comes the important part of upsampling, smooth the new higher speed bit-stream, you have to run the 88.2KHz bit stream thru a digital filter that will try to estimate whether the zero that was stuffed should remain a logic0 or be flipped to a logic1 to make the playback music sound right. There are n number of algorithms to do this many of them are quite sophisticated & almost all of them are proprietary. it is this digital filter algorithm (often called an interpolation filter) that imparts its sonic signature onto the final up sampled music signal. You might like the way the manuf does this interpolation or you may not. And, herein lies the crux of the matter i.e. the effect of upsampling onto the higher bit rate music signal. It is also why so many manuf exist & different people like diff manuf & you rarely get a consensus on who upsampling technique is the best. It's a matter of taste. Often you even see people who have upsampling CD players & DACs where they simply turn this feature off with the press of a front panel button because they say it sounds better without upsampling.
Anyway, that's the skinny on upsampling & its effect on the music signal. sorry it had to be so long-winded but it was important to explain a bit of the background.       

Just listen to the DAC and don't worry about upsampling.  Resulting sound quality depends on much more than that alone.  Can never hurt to understand what it is though.   

I have a non oversampling DAC and others that do.   They all sound lovely.  DACs are like phono carts.  No two sound exactly alike but most these days sound very good.  They need not cost a fortune to sound good though certainly some that do cost a lot sound very good as well, maybe even better.  You really have to do very careful compares to know what you like best.

Bombaywalla, I think that's the first time I understood someone's explanation of upsampling and remembered it minutes after reading it.
:-)
Thanks!

All the best,
Nonoise

https://en.wikipedia.org/wiki/Sampling_(signal_processing)#Sampling_rate

Also, I would have to disagree with chayro’s statement “If you want to make an educated decision, buy a dac based on sound and not specs.” Seems to me it would be best to make an educated decision based on all possible information available. That would include specifications, your own subjective listening, opinions of reviewers, value of the component, etc.

I used to design and implement up and resampling algorithms (and others) for image processing of satellite and aerial photography imagery.

Never for digital audio. The problem is different there but the principles are similar.

DCS Ring DAC technology (expensive) is the one I know of from a few years back that struck me as the best in regards to its ability to randomize noise and produce best results on paper. I’ve heard DCS gear and what I heard was consistent with what I expected.

I wonder to what extent other vendors have done anything similar in recent years to close the gap and maybe even help bring the cost down?

Theoretically, I would rather have a non oversampling DAC done well than an oversampling one done just so-so.

In practice these days, as I mentioned most good quality DACs I hear even at modest cost sound very very good and I care less about the technical details than what I hear, although if buying without opportunity to hear, it never hurts to know how things work in comparison under the covers. Assuming the information provided is accurate and reliable of course. In many cases, its just a black box with little information on how things work. You always only know for sure by listening.

The DAC in my main system is a several years old non-oversampling  mhdt Constantine I picked up used a few years back for less than $400  mainly as an experiment. I’ve never a/b compared to DCS, but the sound reminds me of DCS in many ways and its been a keeper.

Recently I’ve experimented with analog out from newer Iphone and Ipad. The sound is a lot different than the mhdt but surprisingly good and perfectly listenable as well in its own terms.

I also have a Bel Canto c5i digital integrated amp. Its also most listenable and a big hitter in terms of sound quality and features, but sounds much different from the others still.

So lots of very good flavors of digital out there these days at all price points. You just gotta pick a few and try.