Listening to bassist Mark Dresser and pianist Denman Maroney's Time Changes is often like being in a car with someone trying to learn stick shift—smooth coasting is interrupted by sudden lurches, premature downshifts, or unexpected accelerations. To the musicians' credit, though, the music never stalls. By creating tension with so many rhythmically off-kilter sections, the passages where the music settles into a swinging groove come as a surprising relief.

The title should be taken literally. These complex arrangements by Dresser and Maroney focus on frequently shifting meters, tempos, and often polyrhythms among the instruments (percussionist Michael Sarin contributes on a number of tracks, as does mezzo-soprano Alexandra Montano). It's not the most immediately accessible album, but with repeated listenings the music becomes less abstract and warmer and more inviting.

The recording is weighted heavily toward rhythmic exploration and not harmonic or melodic development. Several of the tracks, like the ten-minute "One Plate and "Lateral Mass, take that exploration out to the border of free jazz, but they usually remain tethered by a rhythmic pattern.

Maroney plays what he calls "hyperpiano, which is acoustic, but he includes techniques that sound like playing and plucking the strings in different ways. He creates some interesting effects, getting those strings to sound slappy and scratchy and metallic, and there are some passages, when Dresser is also scratchily bowing his bass, where it's difficult to tell which instrument is which.

Montano's beautiful voice acts as a fourth instrument rather than assuming the role of vocal soloist, singing in plain syllables somewhere between scat and operatic recitative, sometimes doubling the piano.

Tracks to look out for include "M.C., with Montano's ever-climbing vocals and a Latin-ish vamp in the piano and bass; and the funky "Harkemony, probably the best all-out groove on the album, with plenty of polyrhythms and some wild "hyperpiano playing by Maroney.