Two performances on day seven of the TD Canada Trust Ottawa International Jazz Festival demonstrated just how broad a spectrum improvisation can cover. From the idiosyncratic compositions of pianist Vijay Iyer to the more cinematic Sandhills Reunion project by veteran drummer Jerry Granelli, audiences were given the opportunity to understand just why, as time goes on, jazz has escaped definition more and more. Barring reductionist definitions, jazz isn't something you can pin down—but you know it when you hear it.

Vijay Iyer's 4 pm appearance at the Library and Archives Canada Theatre began with an onstage interview by CBC Radio host Andy Sheppard. One doesn't need to hear Iyer speak to know he's a deep thinker—his music makes that crystal clear. But he was an articulate and thoughtful subject, and Sheppard avoided many of the more obvious questions one might ask of an artist who's new to some members of the audience. Instead he just went with Iyer's flow and let the interview evolve more naturally.

On the subject of why he chose jazz over any other form, Iyer said, "I didn't choose jazz; jazz chose me. But the majority of the interview covered his own background, his family's emigration to the US from India, and the current state of affairs in his home country. He explained to the audience that the majority of the concert's material reflected his feelings about what is occurring in the US. Like trumpeter Dave Douglas, Iyer doesn't use his position as a platform from which to proselytize, but his music speaks volumes.

Iyer was joined by a longtime associate, altoist Rudresh Mahanthappa, plus bassist Stephan Crump and drummer Tyshawn Sorey—with whom Iyer has worked in the past, but not for some time. But you'd never know it. Sorey was a flexible player, able to navigate the complex twists and turns of Iyer's compositions and maintain a pulse where necessary, but also open-minded enough to respond to a regular maelstrom of activity around him.

Crump is an equally broad-minded player. He sounds just as comfortable with Iyer's more extreme demands on acoustic bass as he is in the electrified fusion of drummer Gregg Bendian's Mahavishnu Project. He's also capable of resting somewhere in the middle, as manifested by his playing on guitarist/vocalist Joel Harrison's recent records, including Harrison on Harrison. Like Sorey, he covered considerable territory with Iyer, maintaining Iyer's knotty lines but also entering into a more democratic four-way conversation when things dissolved into free abstraction.

In some ways, Mahanthappa is an odd foil for Iyer. He has a surprisingly sweet alto tone—although he's capable of an edge when necessary—and he built solos that were like threading the proverbial needle. At times, he managed to find surprisingly beautiful yet heady lines to weave through Iyer's peculiar patterns. Often beginning with clearly defined motifs, Mahanthappa would develop them in unexpected ways, using extended techniques sparingly and to great effect.

The performance drew mainly from Iyer's last quartet record, Reimagining. Iyer's work may not come from a strict jazz tradition in the way Brad Mehldau's does; he's certainly never recorded a standard on any of his albums. But in the extensive classical background that both share—even if that background is but one source that informs their writing—some comparisons can be drawn. Still, Iyer's ethnicity is also reflected as an ever-present but fully integrated part of his music. His background is, in fact, most noticeable in his interaction with Mahanthappa, who at times bends notes and approaches the microtonal intervals that infuse traditional Indian music.

As a soloist, Iyer is as deep a thinker as his interview with Sheppard suggested. His ideas were not always spare—he executed staggeringly complex linear and chordal forms around the contrapuntal foundation he'd first establish with the group—but they were far from conventional. Iyer's view of the world is deeply personal and well thought-out; his playing reflects a similarly well-conceived aesthetic.

The quartet's relatively short set, while high on energy, was also a challengingly cerebral experience. It met an enthusiastic reception from an audience which, for the most part, knew Iyer's work and what to expect. After listeners demanded an encore, Iyer came out with Mahanthappa to perform a piece from their recent duo recording, Raw Materials. It revealed a different side of Iyer—less intense, but certainly no less intellectual. It also was the clearest indicator of the empathic connection he shares with Mahanthappa, and served as a gentler way to end a set that made considerable demands on its audience.