When Frank London and Lorin Sklamberg of the Klezmatics perform at the Jewish Music Festival next month, the audiences are not likely to hear the rollicking, jazzy klezmer tunes the two are known for.

However, their evening of niggunim, or mystical Jewish melodies, promises to be intimate and spiritual while retaining the energy associated with the Klezmatics.

"Coming at Jewish music from the secular, musical and political side has been an interesting trip," London said recently by phone from his New York home.

"The Klezmatics have always injected their own politics into their music. For example, the Yiddish socialist tradition survives in song. We use that kind of thing to integrate past and present. We go across the generations, across genders.

"But, in the past four or five years. I've developed a strong interest in the spirituality of Jewish music, the mystical aspects as well."

The immediate result of that interest is "Nigunim," a recording that London and Sklamberg made with jazz keyboardist Uri Caine, who will join them at the March 7 event. "Nigunim" is a varied collection, with tunes stretching from yesteryear's shtetls to more recent times, such as one song that London composed in memory of his father.

At the festival, they will perform interpretations of traditional niggunim, as well as original works.

"Niggunim are spiritual songs," London explained, "songs of devotion and praise." They usually are wordless. But sometimes there is a text, usually out of the Bible or more specifically Psalms, which is used as a mantra, repeated over and over.

"One of the most interesting things to me," he continued, "is that, opposed to music say of the church, the niggunim are z'miros, Shabbos songs, meant to be sung at home." The ones London sings come out of the Ashkenazi tradition, rather than Sephardi. Pronunciation follows suit.

"After many years of study and research, we have determined that there is a direct link between music and the language that belongs to it," he said. "You can't separate them."

Accordingly, you will hear no modern Israeli pronunciation of Hebrew words.

Sklamberg provides the vocals and all three play a variety of instruments. The sound, says London, is very personal, "not your standard instrumentation. It's a very acoustic, yet traditional sound."

London, who is essentially a trumpet player, has been playing Jewish music for more than 20 years. He is an original member both of the Klezmatics and the Klezmer Conservatory Band. But klezmer is not all he does.

Recently returned from Japan, where he was music director for a butoh dance piece at a music festival, he presently is producing an album for a Macedonian gypsy singer. He also collaborated on the music for "The Memoirs of Gluckel of Hameln," currently playing at La Mama in New York.

Regardless of his other projects, London said, niggunim have found a special place in his repertoire and his life.

"It's part of a quest for a spiritual view of life."