As well as heterophony, there are some specific types of improvisation in klezmer: 1. The kale-bazetsn (seating of the bride) ceremony. The badkhn (master of ceremonies) made up poems in Yiddish and the musicians played emotionally in between, as part of the point was to make the bride cry. Listen to a kale-bazetsn
2. The doyne (also written as doina) is an improvised piece used by klezmorim to show off their virtuosity. It is generally in two parts with a slow improvisation first, and then a nokhshpil (one or two follow-up tunes) harking back to the roots of the piece in Romanian shepherds' song, so some drones like bagpipe or Romanian-style dance rhythms, ending with a jolly dance. Listen to a doyne:
A badkhn declaims at a Jewish wedding on a Polish postcard from the early 1900s