Digital to analogue converters they are everywhere, your CD player has one your phone has one, increasingly they are built into loudspeakers as part of the DSP chain.
They are first and foremost 'converters' their job is simply that to take a digital signal and turn it into an analogue signal, worth remembering that amplitude and time or amplitude and frequency completely determine a signal.
Dacs became a thing when computers started to be used for audio playback, you needed something to sit between the PC and your Hi-Fi.
As converters their function is to add as little to the input signal as possible, ie no audible distortion.
For some time Amir over at Audio Science Review has been measuring electronic equipment with a sophisticated Audio Precision analyser and he regularly posts their respective measurements in the form of a table that the AP analyser produces its 'dashboard'.
This is the distortion measurement from a very fine measuring although expensive Tambaqui dac,
All measurements are taken at the dacs analogue output literally comparing what goes in to what comes out. We can see in the top right pane that distortion is vanishingly low any artefacts produced by the dac are at minus 135dB, there is some discussion but humans can possibly hear distortion up to 60-80dB so this dac is audibly transparent.
The bottom right pane shows that THD ( total harmonic distortion) and noise is a tiny percentage giving a very high 'Sinad' score of 121dB. Sinad is only one metric but properly engineered dacs always have a high Sinad score.
These are the measurements of a Topping dac/headphone amplifier the DX5 which retails at a princely £400.
We can see that this inexpensive unit actually has slightly better measurements than the Tambaqui despite being one 20th of the price.
Despite the Topping having marginally better measurements there will be absolutely no difference in sound quality between the two dacs, no difference whatsoever.
Both dacs measure superbly, both are audibly transparent.
Despite what you might read in a products marketing or hear from some 'influencer' there will be no difference in sound quality none, nothing nada.
As a prospective buyer a more expensive dac might have a smarter 'milled from solid' case perhaps a solid aluminium remote it might well have additional features that might be useful but in terms of absolute sound quality there will be no difference.
Next time we will look at some poorly measuring dacs and ask how much distortion do you have to add so that you can hear actual differences between dacs.