On the debit side: Well, I could use more in the way of words. It's a bad sign when you're listening to a setting of the Mass Ordinary and aren't always sure where you are in the text. This was not good for the Missa in illo tempore, and if anything it was worse for the wordier music surrounding and following it on the program. And there were the odd signs of under-rehearsal as well. Monteverdi is fond of startling harmonic juxtapositions, but they're intended to startle the audience, not the singers. There were several points in the Mass (the beginnings of the "Et incarnatus" and the "Benedictus" come to mind) where the eventual solid chord began as an audible work in progress.

This Mass is a famously hard nut. There's a reason that many who know and love Monteverdi's 1610 Vespro della beata Vergine don't know that it was published along with a Mass setting, let alone that the Mass takes pride of place in the partbooks and on the title page, with the Vespers not-too-successfully disguised as a sort of afterthought. Monteverdi's Mass is what is called a "parody Mass." The term has nothing to do with humor, and merely means that the raw thematic material was drawn from a pre-existing piece. In this case it was a very old piece: a motet of Nicolas Gombert, who belonged to the generation after Josquin des Prez, and had died over 50 years earlier.

Monteverdi's work was obviously intended as a demonstration of his versatility and his contrapuntal skill. Nearly everything in the Vespers is built around pre-existing music, be it nothing more than a Psalm tone. The Mass also shows the composer tackling older music, though in a different and more venerable style. And he made sure it was noticed: The subjects ("fughe") drawn from Gombert's motet are proudly published at the front of the continuo part. Monteverdi had reason to be proud, because the work is as polished a piece of counterpoint as you are likely to find anywhere. All the same, it's a hard work to love, partly because the incessant working-out of contrapuntal possibilities and the already dense Gombert manner, combined, make it too rich for comfort.

Wallace devoted a large chunk of her program notes to explaining her decision to perform the Mass a minor third below the printed pitch. Those diligent few who have followed all the performance-practice squabbles about the 1610 Vespers will remember that a few of that work's numbers were printed in chiavette, "high clefs." There is good evidence from a number of sources that there existed a convention of notating music in what looks like a high absolute pitch, but with a combination of clefs that indicated to readers that the actual performing pitch should be a fourth or so lower. The Mass is also printed in chiavette, and accordingly Wallace pitched it in A, rather than the printed C. Why she didn't do the same with the posthumously published Laudate pueri that separated the Mass's Gloria and Credo on the program, I don't know, because that is also in chiavette, and in the context of the two low-pitched Mass movements on either side of it, it sounded extremely high. (Higher even than written, to my ears; I could've sworn that it was up a whole step.)

The discursion on chiavette was the more odd because the notes altogether skirted what most listeners would find a much more pressing performance-practice issue: How many on a part? There are plenty of fine string-orchestra versions of string quartets, but ordinarily if you undertake to perform a string quartet with a string orchestra, you make mention of the fact somewhere. Singing madrigals in chorus is a comparable alteration of the music, and some comment on the practice, if only a word in defense, would have been welcome.

In fact, the practice is defensible — up to a point; and the California Bach Soloists made that clear. At its best, the madrigal half of the program was very good indeed. The standouts were Jacques Arcadelt's Il bianco e dolce cigno (The sweet white swan) and Monteverdi's Ecco mormorar l'onde (Hear the waves murmur). The latter, which ended the program, is a magnificent piece of tone-painting: a sunrise, colorful and brilliant, and running (in Friday's performance) in one great arc from beginning to end. The Arcadelt, a more modest piece, was if anything even better sung; something about its homophony and the easy swing of its rhythms brought out the choir's best.

Elsewhere the choral-madrigal idea fared less well. The more chromatic numbers, like Giuseppe Caimo's Piangete valli (Weep, vales) and Monteverdi's taxing Ah! dolente partita (Ah, sad parting), suffered only from a little pitch insecurity. In Monteverdi's Io mi son giovinetta (I am a young maiden), though, the choir wasn't remotely up to the passagework, let alone the sassy tone of the text and the music. And Si, ch'io vorrei morire (Yes, I want to die!) — from Monteverdi's Fourth Book of Madrigals, like the last two mentioned — was just a mistake. The "death" of the title is purely metaphorical — nay, even (dare I say, given the rest of the text?) "tongue in cheek." Monteverdi's setting outdoes the text in sheer, breathless erotic intensity, which is saying something, if you know the text. Friday's performance was just, well, not remotely sexy enough. "Ahi, car'e dolce lingua ... Ahi boca! Ahi bacci! Ahi lingua!" (Ah, dear sweet tongue ... Ah mouth! ah kisses! ah tongue!) sounds somehow more sensual when sung by one voice rather than a section, but even a choir ought to be able to generate more heat from such kindling.