Persian music usually starts with a rhythmic introduction called pishdarâmad, and is followed by an arhythmical piece called darâmad. It continues with a more rhythmic piece entitled châhârmezrâb. After the instruments introduce the modal atmosphere, the singer starts improvising on a free rhythm in accordance with the poetic meter. The instrumentalists follow the singer after a short delay, and repeat the melody periodically, between each sung verse, in an identical way or with a slight variation. This repetition is known as djavâb-e âvâz or 'song-response'.