From reading a few posts on this board, there still seems to be a bit of confusion what tracks John Frusciante appears on for De-loused in the Comatorium. He only plays on one song: "Cicatriz ESP". Apparently the GSL site said that he played on 2 tracks, but all other interviews with the band members themselves indicate that he only played on one album track. The confusion lies in the fact that Frusciante played 2 different instrument tracks on "Cicatriz ESP": guitar and A100 treatment...
Just one of many interviews that confirms it was only one track...
RC: He just played on one track?
Cedric: Yeah he [John Frusciante] played on one track. He does like on "Cicatriz ESP", when it breaks down in to this ambient part, he does a lot of the affected parts. And he also does a dueling solo, it sounds so funny dueling solo, but he does like a dueling thing with Omar on there.
RC: Like doubles it out?
Cedric: Yeah, he just got off the plane, came over, and I watched them do it. It was fun.
The "A100 treatment" refers to a kind of synthesizer that John used on "Cicatriz ESP"...along with lot of his own solo projects...
From Electronic Musician - "John Frusciante's Creative Explosion"
So apparently the A100 and similar synthesizers can be used for treating other instruments...as well as to produce sound effects on their own.
Although he is known as a guitar player, Frusciante is also an enthusiastic synthesizer user. Not surprisingly, his synths mainly date from the late '60s to early '70s. His collection includes a Doepfer A100 modular synthesizer, a Mellotron, a Minimoog, and a 1970 ARP 2500. "For a long time I was using mainly the Doepfer. I was more interested in using the LFO and gates treating other instruments with it. I wasn't interested in using a synthesizer's oscillators. But the ARP 2500 has renewed my interest in oscillators completely, because they sound incredible. It's the same thing with guitars and recording equipment-the old stuff sounds better, louder, warmer and more soothing.
Frances The Mute
As for Frances The Mute, Frusciante plays the first two solos on "L'Via Viaquez".