Musically speaking, Hasidic nigunim vary enormously in style, form and feeling. Some are slow and meditative, others fast and jubilant. Nevertheless, they generally share certain basic features: They are songs formed of multiple melodic phrases, typically sung without instrumental accompaniment and without words. This last feature, while not found in every Hasidic nigun, is one of the genre’s most distinguishing characteristics. In place of words, repeated “nonsense” syllables (such as bam-bam-bam and doi-doi-doi) are used. Nigunim are also performed in a distinctive expressive vocal style with dramatic inflections similar to cantorial music referred to by the Yiddish words krekhts (lit. moan, sigh, or sob) and kneytsh (lit. pinch).
By Dr. James Loeffler, My Jewish Learning