The Clerks' Group didn't make it easy for themselves when they began their Ockeghem survey on ASV with the notoriously elusive Missa Mi-mi. With its somber modal sound and low vocal range, the Mass is very appealing in its way, but there's no plainchant melody or other structural device to help performers get a handle on the work--it's easy for the singers to lose focus and drift into a melancholy haze. Wickham and his singers avoid that pitfall nicely: singing with full-bodied tone, they keep the momentum of Ockeghem's seemingly wayward lines clear and bring out some lively rhythmic detail not usually associated with this composer. Alongside the Mass, they've included five motets: two by Ockeghem and three by his compatriots Busnois, Isaac, and Obrecht. All are beautiful--and beautifully done--but the standout is Isaac's "Angeli, archangeli," its bright scoring, animated rhythms, and soaring treble parts making a delightful contrast to the Mass. (For a remarkable, if unusual, rendition of the Missa Mi- mi, try the Cappella Pratensis.) --Matthew Westphal