The processional (a.k.a. the entrance of the wedding party) marks the start of the ceremony and is a highly anticipated moment, so it's important to arrive on time. In Arabic this is known as the 'Zaffah' . This will be loud with drums, as its purpose is intended to 'let it all be known' in a celebratory way to witness the marriage union of the bride and groom in holy matrimony. It is perfectly fine to sing, clap, or just stand and watch.