We are not alone

The synthesizer used to communicate with the aliens at the end of the film is an ARP 2500 modular system. Phil Dodds, a tech from ARP Instruments Inc., is the man playing the keyboard. The motif woven through the film (the five tones that the space ship plays back and forth with the humans) is re - mi - do - do (octave lower) - sol. These tones all lie on a major pentatonic scale. The motif was developed to resemble Hello (H-E-L-L-O) in musical form. Steven Spielberg remarked that "it shouldn't even be a melody: it should be more like somebody pushes a doorbell. Like Avon calling—you know. 'Ding Dong.' It's not a melody. It's not even a phrase. It's just musical intervals. With no rhythm assigned to them or anything. Just five notes." [Wikipedia]

[soundonsound.com]
[createdigitalmusic.com]