Im really a bit confused about this topic…
two computers without sync will drift
( bare in mind this means desktop computers need to be disconnected from networks, to stop them ‘cheating’ ;))
so having two instruments without any sync at all is, well, pointless. why would you even do this?
so i did at test, so i could given ‘practical’ rather than just the theory
I had Live connected via USB , using midi clock as sync… the timing was identical after 90+ minutes (+/- jitter)
which is exactly the behaviour i would expect (from the theory perspective)
basically with two sync devices, they should remain in time +/- jitter. thats the thing with an E-RM clock, it doesn’t do anything for drift, it just helps jitter…
i.e. if you have +/- 2ms Jitter on (usb) midi clock then after 60 mins, your beat should still be +/- 2ms, the E-RM will just make it +/- 1 sample.
as to how accurate a individual clock is, that pretty irrelevant, surely, in a musical context, time/timing is relative.
no one sits listening to music and says… oh my god thats 120.1 bpm, and its varying by 100ms over a 30 mins… what they notice is that things become out of sync with each other
ok, they might notice it switch from 120 to 130 bpm, but no where here are we talking about such inaccuracies… 1/16 note at 120 bpm is 125mS … over an hour, that is a tiny shift
seems to me too much obsession with ‘the grid’