The key objects in gen~ are delay and a phasor.
With the modulation of the delaytime you can simulate a kind of a Doppler effect. It’s not quite a pitch shift, but it’s a frequency shift. It will transpose the whole harmonic content.
The shift will be: 1-((pf)*modrange/1000
With pf= frequency of the phasor
modrange = Modulation range for the delay im ms (I think the delay object in gen~ needs samples)
The easiest way for calculating the shift will be, if you modulate the delay time with a phasor in the range of 0...100 ms.
-> shift = 1-(pf*0.1)
For a shift of 1 octave down
0.5 = 1-pf*0.1 -> pf=5
For a shift of 1 octave up
2 = 1-pf*0.1 ~> pf=-10
There ist a cool tutorial for msp~ on YouTube, but it’s easy to translate it into gen~