Mikey those keyboard players who told you this are very wrong, it is the other way we use after touch in Arabic music as much as western music.
The 1st great keyboard player who used to apply vibrato to his solos was Hani Mehanah he is the 2nd keyboard player to play Arabic music with Oum Kalthoum and Abdul Halim Hafez.
He used to use the slider on his Keyboard to apply the vibrato when playing solo and after they came out with after touch which you apply pressure on the keys to get some kind of effect as programmed in your keyboard every one started using the after touch for vibrato, Tarek Akef one of the great keyboard players and arranger uses this method a lot in his playing and now we all love it and use it.
On my Kurzweil I have so many options for after touch (you can bend notes or change the cutoff frequencies and more) this method is called MODULATION.
I hope this article will help you understand after touch and try to use it as much as you feel (its all about feelings) Vega is one keyboard that does not have the after touch but if you really need to use it you can do it with the pitch bender but pushing it up, then again if your left hand is busy with changing chords tough luck.
It’s always better to use 2 keyboards one for arrangement and the other for solos.
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Abdo