From page 9 of the liner notes for ROTJ:

"TATTOOINE RENDEZVOUS (2), most of which accompanies a sequence eliminated from the film. in it, Vader uses the Force to contact his son Luke Skywalker. the tone of the music changes with the appearance of a synthesizer and dissonant strings, which williams uses to gracefully the setting to the desert planet of tattoine. The next thirty min- (to page 10) utes of music are imbued with dark complexity as luke and his companions embark on the rescue of (paraphrase) han from jabba.(end) Eerie tonailities of wailing woodwinds and abrasive brass seem to come from the enviroment itself as the heroes encounter a den of bizzare alien creatures. The sequence begins with the brief telepathic exchange between luke and vader, which is broken by the appearance of artoo and threepio acompanied by lukes theme aand a bouncing wind melody as lukes places his new lightsaber inside artoo's dome. this motif continues as heard in the film"