12kHz might be on the very far side of it, and maybe don't get up there.
The different channels on the other hand need to be quite exact.
simulating the frequency of a wheel with 2 teeth freq = 2 * ( (10*rpm) / (60 * 0.291) )
1 rpm I get ~1,3831 hz => 722999usec
8000 rpm ~11065.007 hz => 90.375usec