This latest release by the early music group Huelgas Ensemble tackles the difficult feat of the isorhythmic motets of Guillaume Dufay with great success.

An isorhythmic motet takes its name from the repetition of a specific rhythmic pattern spread through a given vocal line. Because it allowed songs to be grounded in fairly long rhythmic patterns, it afforded Renaissance composers the freedom to work on a much larger scale. These unifying patterns were often arranged to diminish in scale over the course of a piece, eg. 3:2:1. The result was not music to please the ear, but rather to display the intellectual and rational side of the composer.

The Huelgas Ensemble presents the complete 13 motets by Dufay, which together comprise a 25-year experiment. Though the group fails to put the motets in chronological order — which would have given the collection a better sense of direction and flow — the album nevertheless showcases a splendid blend of singers joined by a delicate quartet of instrumentalists that includes flute a bec, sackbuts and vielle.

One highlight of the disc is the trio "O Sancte Sebastiane" (RealAudio excerpt) which dates from 1437 and may be a tribute to the Council of Ferrara. Of continuing interest in all of these selections is the reliance on awkward chord progressions just before the final cadence. This can be heard especially in the "Ecclesie Militantis" (RealAudio excerpt) of 1431, a tribute to the election of Pope Eugene IV.