MUSIC : With Baroque, It Seems, Nothing Is Simple : For the Corona del Mar festival music director Burton Karson, conducting early music forces some difficult choices.

Medieval philosophers used to debate how many angels could dance on the head of a pin. The issue may sound frivolous today, but at the time it stirred questions about logical reasoning and the nature of materiality.

Modern conductors have to resolve similarly abstruse-sounding but important issues when leading music of the Baroque era if they want to adhere to what is termed “correct performance practice.”

Burton Karson, founding music director of the Corona del Mar Baroque Festival, which continues through Sunday, recently said he spent 15 minutes working with his musicians just to get a trill right.

“There are two or three ways to trill,” he said, “and several ways not to.”

The issues, Karson says, include “which notes to start on, how many you do, whether you hold the first note as an appoggiatura (an auxiliary note used an ornament), and how long you hold it. On a repeat, you do it differently. You never do it the same way twice.”

Karson said he may leave such decisions up to soloists. “But I must get involved when a phrase goes from section to section or from person to person--when there’s a conversational aspect to it. Then they have to do it the same way.”

Karson admitted that making such decisions doesn’t make a conductor popular among singers and instrumentalists. Performers, he said, “very often balk at such discussions because they feel they’re going to be scholarly or difficult. Vocal soloists are usually more difficult to work with because ornamentation is more difficult on a human voice than on a violin, oboe or harpsichord.”

And even when sensitive musicians make acceptable choices, there still remains room for debate.

Although his singers were making “logical and correct choices,” Karson said he often simply “preferred a different ornamentation.

“They were starting to trill immediately,” he said. “I asked them to hold the notes so we had a more pungent dissonance resulting from the appoggiatura which begins the trill, not just a flutter of sound. The text was pungent. By holding the dissonance, I illuminate the text more meaningfully.”

The singers liked the change, he said. It also made it easier for them to sing.

“I don’t want to sound as if there are two ways to do something--the wrong way and my way,” Karson said. “That’s rarely true. Often I can accept their choice if it sounds relaxed and comfortable and musical, if it’s appropriate.”

But the best laid plans can go wrong, he noted. “Sometimes, performers forget our decisions, and in the performance I hear differences and suffer.”

Finding the right singers also is an issue, he said. Countertenors, male altos and especially castrati were the virtuoso singers of Handel’s day. Mercifully, that last vocal category is no longer available. Karson chose to use a female alto for Handel’s “Acis and Galatea,” to be sung Friday.

“Sometimes I wonder: Would it have been better to use a male alto or a countertenor?” he said. “He would be singing higher in his voice than an alto is singing in her voice, and that would give a more brilliant sound. . . . But I accommodated to what is available.”

Purists would also argue that to be truly correct, the musicians must lower the standard pitch used today (the A note equals 440 vibrations per second) to the pitch used during Handel’s day (somewhere in the vicinity of 415 vibrations per second).

Karson said it is a matter of practicality. “We have used lower pitch when it was possible,” he said, “but when you’re using many different instruments, as we are doing, some can and some cannot accommodate to the different pitch.”

But he does try to adhere to the way in which stringed instruments were bowed in those days.

“We bow in as accurate a Baroque manner as we can,” he said, “slurring only when the composer indicates it, as in the case of Bach, or when the musical line clearly demands it.” Similarly, he holds string vibrato to a minimum.

Karson said that although little controversy remains about such issues, the “hottest debate is whether or not to use period instruments.” But even getting ahold of instruments made in the 17th or 18th Century by such great masters as Stradivari, Guarneri or Amati may not be the answer.

“All of the great old violins have been modified,” Karson said. “They had their necks lengthened about an inch so that steel strings could be mounted and be put under greater tension to provide a more brilliant sound . . . .

“It’s an endless debate. But at some point, you have to make the music work and make a decision to go ahead. Once you’ve decided you’re using modern instruments and modern singing techniques, then you make it as Baroque as you can without violating the actual instrument.”

The 10th annual Corona del Mar Baroque Festival continues with concerts tonight and Friday at the Sherman Library and Gardens, 2645 E. Coast Highway, and concludes on Sunday at St. Michael and All Angels Church, 3233 Pacific View Drive. All programs begin at 8 p.m. Tickets: $15. Information: (714) 730-0499.