The dhol is a double-sided barrel drum played mostly as an accompanying instrument in regional music forms. In qawwali music, the term dhol is used to describe a similar, but smaller drum used with the smaller tabla, as a replacement for the left hand tabla drum. The typical sizes of the drum vary slightly from region to region. In Punjab, the dhol remains large and bulky to produce the preferred loud bass. In other regions, dhols can be found in varying shapes and sizes and made with different woods and materials (fiberglass, steel, plastic). The drum consists of a wooden barrel with animal hide or synthetic skin stretched over its open ends, covering them completely. These skins can be stretched or loosened with a tightening mechanism made up of either interwoven ropes, or nuts and bolts. Tightening or loosening the skins subtly alters the pitch of the drum sound. The stretched skin on one of the ends is thicker and produces a deep, low frequency (higher bass) sound and the other thinner one produces a higher frequency sound. Dhols with synthetic, or plastic, treble skins are common.