Bob Ostertag (New Mexico, 1957) was raised in Colorado, studied at the Conservatory, and in 1976 picked up the synthesizer and formed the improvisor ensemble Fall Mountain with Ned Rothenberg (reeds) and Jim Katzin (violin), later documented on Early Fall (may 1978 - Parachute, 1979) and extended pieces such as Ultima Thule and Small Life, thus becoming one of the first improvisors at the electronic keyboards.

In 1978 he joined Anthony Braxton, and in 1979 he relocated to New York, where he became part of the "creative" scene. His first album, Getting A Head (may 1980 - Rift, 1980), was a trio with guitarist Fred Frith and drummer Charles Noyes, and Ostertag playes all sorts of electronic and self-made instruments. More importantly, this was an improvised jam session, with Ostertag improvising on tape manipulation, a first in improvised music. Getting A Head begins with a mindblowing bedlam of electronic winds and guitar noises, but the rest of the piece is a stream of shapeless bleeps and hisses. In Tundra manipulates some chaotic tinkling until it morphs into an ear-splitting wall of noise. After taming this fireball of musique concrete, the piece shifts to Frith's and Noyes' random clangor. Then the clangor slowly morphs back into the initial tinkling, so one can now appreciate where it came from. In Tundra would remain one of the master essays of fusion of musique concrete and free-jazz improvisation.

Voice Of America (january 1981 - Rift, 1983) documents live concerts with Fred Frith in which Ostertag displayed the same skills at electronic improvisation and added a new technique to his bag of tricks: sampling (achieved with a stack of tapes because the sampler had not been invented yet).

Distracted by his political activities (supporting revolutionary movements in Central America), Orstertag returned to recording only after a seven-year hiatus but armed with a sampler: Attention Span (december 1989 - Rift, 1990) featured Frith on guitars and John Zorn on saxophone.

Sooner or Later (june 1990 - RecRec, 1991), an ambitious work of musique concrete, is a set of variations on the crying of a Salvadorean boy. Initially Ostertag simply manipulates the boy's voice to emphasize the pain, but then the voice get transformed into something completely different, a flux of wavering electronic tones that one can only remotely relate to the original source. The voice then resurfaces here and there, but stretched, deformed and warped in all directions. The ending is an apocalyptic explosion of both the abstract electronic noise and the recognizable bits of voice.

A protagonist of the gay-rights movement, Ostertag payed tribute to the San Francisco gay riots with the string quartet All The Rage (1992), that combines audio-verite recording of the demonstration and hysterical counterpoint, and Burns Like Fire (MVORL, 1992), that employ popular music as well as sounds of the riots (and string instruments) as sources.

Say No More was a virtual quartet with drummer Joey Baron, bassist Mark Dresser, percussionist Gerry Hemingway. Their group music on Say No More (1993) was actually composed by a computer and sampler from separate individual performances. The piece is sandwiched between two hyperkinetic jams driven by pummeling acrobatic drumming. In between, it indulges in all sorts of atonal exchanges and mutations, with the computer basically creating a form of hyper-virtuoso playing. The second side of the LP contains a much looser and calmer jam whose main protagonists are (manipulated) voice tapes. In Person (1994) was its dual live version, which is a lot less "virtuoso" and much more disjointed and atonal: humans imitating computer music instead of a computer imitating human players. Say No More reformed for Verbatim (may 1996) and its dual Verbatim Flesh & Blood (2000). On Say No More he simply "conducted" the music, whereas on Verbatim he actually performed (on the sampler). The result is surprisingly much more subdued. The initial section has some doodling by the rhythmic section to support liquid dissonant sounds. This largely faceless stream of consciousness continues for 24 minutes. The second part boasts more virulent drumming and some chaotic interplay but nothing approaching the maelstrom of the first album. Because Ostertag performs in person at the sampler, the dual live album, Flesh & Blood, is actually more interesting than the previous dual album. This was Ostertag's attempt at composing for improvisers (by using their own improvisation as the score).

Fear No Love (1994), with Mike Patton, Fred Frith and others, was unusual in that it mixed rock, soul and dance music.

Like A Melody No Bitterness (Seeland, 1997) was a rare case of solo improvised music for sampler. On one hand, Ostertag creates a rhythm out of some cryptic effects while, at the same time, he modulates voices to make it sound like they are singing a melody. After a section of wild instability and whirlwinds of noise, the piece enters a stage of minimalist percussive pianola music. That slowly disintegrates into a chirping mess, which in turn evolves into a lightning-speed mash of shattered glasses and cartoon soundtracks. This collage of musique concrete keeps spinning via tribal bleeps, jungles of hisses and warped voices. One of the best effects arises seven minutes from the end, sounding like a swarm of evil insects crossed with some dj scratching. The latter eventually prevails, accompanied by a syncopated beat.

Ostertag also collaborated with Otomo Yoshihide both on Twins (Sank-ohso Discs, 1996), and in House of Splendor, featuring drag-queen Justin Bond and rechristened PantyChrist (Seeland, 1999). The album includes the cartoonish pianola dixieland Feet So Low.

Ostertag also scored multimedia pieces such as Spiral (1996) for self-made glass instruments, film and spoken-word, Yugoslavia Suite (1999) for digital music, video and hand choreography, Entre Basura y Ciencia (2000), etc.

In 1998 he embraced the laptop computer. During the 2000s Ostertag collaborated with vj Pierre Hebert in live performances.

The Book of Hours (2012) is an ambitious experiment on the human voice (featuring vocalists Theo Bleckmann, Shelley Hirsch and Phil Minton), on rhythm (indirectly created by the computer manipulations) and on improvisation (including saxophonist Roscoe Mitchell's contributions); a carefully assembled (and dis-assembled) stream of consciousness that manages to concoct both jazz and rock overtones out of machine music. Particularly powerful are the progression at 10'25" and the breathing section at 14'09".