A UGen that returns time since last triggered. The time returned is in seconds
and is measured from the last received trigger. Note that currently it seems the
initial memory is at -1 sample, so for Impulse.ar(1) the result (at 44.1 kHz)
is 2.26757e-05, followed strangely by 1.00002, and then (as expected) 1.0.
the trigger to update the output signal. A trigger
occurs when trig signal crosses from non-positive to