DAC measurements explained?

Probably a good place to start is in the Stereophile reviews. Lots of DAC's measured there and free to view.

But, just in general, you have 0s and 1s in a CD, or file, or stream. Measuring a DAC measures how closely to an idea reproduction of the music the DAC can come to. Bits in, analog out.

Noise, jitter, linearity and frequency response are the big ones, and their value is arguable. I mean, once you get below a certain point, it's hard to prove things matter.
Can you hear the difference between 0.01% distortion and 0.00001%? most don't think so.

I think the best things that most measurements can tell usu about a DAC is whether the designers and manufacturers paid reasonable attention to detail for the money they are asking. :)

In the case of headphone amp / DAC combinations, you can tell a little about how well they will do with different headphones too.

Besides Stereophile, here is a great review (I mean well written) of a headphone/DAC that goes into some detail.

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-topping-dx3pro...