Properties of Sound

Can anyone explain to me how or why is it that the speed of sound does not change when the pressure increase?

And why speed of sound in air increases when density decrease? This part is real funny to me as since sound travels faster in solids which is denser then gas speed of sound in air should decrease with density…as far as i picture it.

According to info on this page, your assumption is incorrect:

Hope this helps.

The greatest factor in the speed of sound of a gas is the speed of the gas particles. At a given temperature and pressure, lighter molecules are moving faster, so the speed of sound is greater. When the pressure is increased, but the temperature is held constant, there are more molecules per unit volume, but the individual molecules are moving at about the same speed, so the speed of sound doesn’t change (much).