Hushaym (may Allah have mercy on him) says: the beating of the duff is at marriage. Abu Ubayd (may Allah have mercy on him) says: Some people claim that al-duff is a dialectal form, and that in the report it is with a fatha; and as for "al-sawt" (the sound), some people take it to mean al-sama' (listening to music), and this is a mistake. In our view its meaning is the announcement of the marriage, making a sound about it, and making it known among people.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14695