Get a noise gate that you can control the attack and set it to slightly slower attack so it almost works like a volume pedal swelling really fast on each note. I used to use a gate in an SPX90 rack unit to do that kind of sound. If it's constant, rhythmic on tempo, you can also use a tremolo effect and play in time with it and it will swell in like a synth on each note like that. Pink Floyd's "One Of These Days" was done like that, as was the guitar of The Smiths "How Soon Is Now?"
Also has some kind of chorus or flange sound on it.