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The analog waveform that our amp wants to see is produced by the DAC's (Digital to Analog Converter). If you think of a DAC doing a similar operation to calculus (i.e. using infinitely small slices to approximate curves etc) then the higher the bit rate and bit size would allow for a more precise approximation of the analog waveform in the time domain. Imagine a staircase: If you had a 10 foot rise and used 10 steps at 12" high to get there, you could easily discern the steps. But if you used 120 steps at 1" high, it would look very similar to a smooth surface. That's why (I think) the better your DAC is, the better your analog output to the amp would be. The specifics of DAC design (successive approximation, oversampling etc) are a bit (no pun intended) beyond me for sure.
Where is the limit of human hearing? I have no clue, but the better a signal is, the better it could sound, even if we couldn't hear the difference.
That's my understanding at least. If there’s a DAC designer out there, I’d love to hear his/her take and a correction to anything I may have misstated.
S.