OK, I get your point now !

As UD wrote : The sampled sounds are SAMPLED with all typical effects included.

A sax-sound changes in more than one way when time 'passes' :

Attack, envelope, volume, harmonics, brightness, volume-modulation (tremolo), windsound/noise and frequency-modulation (vibrato)

So it is absolutely 'natural' those things happen IMHO.

for example :
A vibraphone has build-in vibrato. Who wants to add vibrato with the use of the modulation wheel ?

UD is right : Just pick another sound that has no vibrato.

Roel

btw I live in Europe