[PD] audio less than or equal, greater than.. cross threshold?

[Alex]

I want to trigger an event when an incoming audio signal (which i know
is a ramp between 0 and 1), crosses some threshold.

basically i want something like

[adc~]
|
[last sample <= x && cur sample >x]
|
[a drum or something is triggered]

any ideas how i can do that?  I don't see how I'd do it with just the
built in objects.
I realize that the bang will probably only happen at control rate..

I have another app creating this ramp, and I want to be able to sync
to it in pd [probably just to trigger drum samples]

-Alex