You can also use metro to create triggers with a random chance of getting
output.
In the following ,
kresolution is the frequency of the metro,
and
kprobability is the probability that a trigger will be output.

This setup creates bipolar triggers,
just comment out the
 kneg = kneg * -1
line if you only want positive trigger values

;*******************************
 kmetro metro kresolution
 if kmetro == 0 goto skip

 idist = 0.5   ; triangular random distribution
 krand rnd31 1, idist

skip:
 kthresh = 1 - kprobability ; threshold for generating a trigger signal is
inverse propotional to kprobability
 kplus trigger krand, kthresh, 0
 kneg trigger krand, -kthresh, 1
 kneg = kneg * -1
 ksig = kplus + kneg
;*****************************



best

Oeyvind