Isaac's discography has seen a marked upturn in the last year, and is here increased further by Rebecca Stewart and Cappella Pratensis, who present one of the composer's settings of the Mass for Easter Sunday. These were composed for the Imperial court at Innsbruck, and follow its established tradition of singing only alternate verses polyphonically, leaving the others either to be sung in plainchant or improvised (upon the plainchant) by an organist. Isaac's six-voice setting has been recorded by The Hilliard Ensemble using the former option (EMI Reflexe - nla) ; here the latter, musically more intriguing alternative is adopted for the five-voice setting. Wim Diepenhorst improvises on the Ebert-Organ at Innsbruck (a mid-sixteenth-century instrument) in the style of Paul Holfhaimer, Isaac's organist colleague at Maximilian's court. I know of no other CD in which alternatim organ rendition is used through the whole recording, and the result is worth a recommendation for its own sake. Diepenhorst's improvisations are stylistically very well judged. They show off a lovely instrument to great advantage and make one hope that this well-documented manner of performance will be preferred by future performers. Incidentally, Cappella Pratensis travelled to Innsbruck to make the recording, so there are none of the awkward breaks that occur when choir and organ are recorded in separate locations (as is often the case in ventures of this kind).
The disc includes not only the Mass Ordinary but Isaac's setting of the Easter Propers from the Choralis Constantinus. Here too, the organ is used to alternate with the choir, though whether alternation is appropriate in the Propers seems to me slightly more problematic; nevertheless, as the polyphony is based on chant it is certainly feasible. In a previous recording (of Ockeghem's Mi-Mi Mass, Ricercar, 2/99) I enjoyed Stewart's idiosyncratic approach to ensemble sound; but here the result is less convincing. In particular, the tone of the sopranos is rather thin; deliberate it may be, but there is a hint of insecurity in the delivery, and for some listeners the result may well wear thin with repeated listening - particularly when this impression is reinforced by other mannerisms (in the plainchant, for instance). Finally, the disc does not include 'all the music for the Mass of Easter Sunday as composed by Heinrich Isaac' (pace the booklet-notes). The Orlando Consort has recorded all the Propers elsewhere, of which Stewart misses out the Prose; and Isaac wrote three more settings of the Ordinary besides this one. Never mind: ultimately it is the recording's conception that matters here, and it carries the day.'