Sound waves are longitudinal wave which propagates in form of compression and rarefaction through the medium
As the medium is have compression and rarefaction then we will have few positions in the medium where we have pressure maximum and few points of less pressure.
this pressure difference creates disturbance into our ear drum and this disturbance or this signal is convey to brain as sound.
The transmission of this signal is always in form of electrical signal which are carried by neurons into our brain
So the sound waves are converted finally into electrical signals in order to be processed by the brain.Read more on