I found this thread on gliss started by musicpete:
I am afraid I think the glissandi with portamento sounds really awful. When I notate the gliss in Sibelius it sounds much better. When I turn it into a midi file and load in Tracktion, you can see there is pitchwheel data instead of portamento. But unfortunately something is going wrong in the midi translating because it sounds really weird. I can't get it sound the same as in Sibelius.
Does anyone have this experience? Some tips perhaps? What are your methods of creating realistic string gliss?