How does the sound produced by a vibrating object in a medium reach your ear ?

Sound produced by irregular vibrations of a material is

How does a gecko produce sound ?

We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?

Assertion (A) : The pitch of the sound produced by the vibrating string can be changed. Reason (R) : The pitch of the sound can be changed by changing the length, tension and thickness of the vibrating string.