In the wet air, the atmospheric air becomes moist than in dry air. So, the humidity on wet or rainy air is more than the dry air. Greater humidity present in the air decreases its density. We know that the velocity of sound in air is inversely proportional to the square root of its density i.e., \(v\propto\frac1{\sqrt\rho}\). Therefore, a decrease in density causes the velocity of sound to increase. Hence, sounds heard better on a wet day than on a dry day or on more damp (moist) air than dry air.