Thanks to both of you - very helpful and fast. Seems like this is what I was searching for. @bocanegra, thanks also for the explanation.

I want to build a patch which acts like the gate input of eurorack's "maths" module, with dedicated rising and falling times at the beginning of a gate signal resp. at the end.
I.e. a square wave will get kind of a trapezoidal signal form with specific rise and fall times.

For testing purposes I made the following simple patch where the phasor's frequency can be changed. The threshold~ sends a bang and a small 1ms square wave signal is synthesized with the vline~.
But there seems to be an upper limit of the frequency of around (at least on my computer) 350Hz. Can not hear a tone with a higher pitch, with lower frequencies there is a kind of FM sound.
My question is: where is the problem in generating bang frequency higher than 350Hz? What is an alternate patch to get a bang signal at the raising edge of a signal and another second bang signal at the falling edge (like in threshold)?