There is a hole in this outer covering which exposes the main membrane below. This annular membrane is much more prominent in the mridangam than in the tabla. There are items placed between the main membrane and the annular membrane that further accentuate these differences. Tabla often has a string placed between the annular covering and the main skin, while mridangam has straw. This may not appear to be a significant difference but the purpose of these insertions is diametrically opposite.
String is placed in the tabla to lift the annular membrane and reduce the dampening effect.
However the mridangam has pieces of straw placed radially between the two skins. This actually increases the dampening and acts as a snare. Both tabla and mridangam are characterized by a rich and varied tone. Some strokes evoke clear pitched sounds while others evoke unpitched sounds. The rim stroke is a major stroke on both the tabla and the mridangam.