Answer: The inner ear is the part of the ear responsible for this
Explanation: The cochlea which is located in the inner ear is responsible for the detection of pitches. The cochlea has tiny specialized hair cells which help detect sound pitches i.e. the volume of different sounds based on where they are located in the cochlea (either the outer or inner cochlea) or based on the length of the microscopic hair protusion.
Cells with short hair protusions located in the outer part of the cochlea close to were sound enters the ear detects high pitched sounds, while the cells with long hair protusions located in the inner part of the cochlea is responsible for detecting low pitched sounds.
It is important to note that not every hair cell in the cochlea responds when a sound is made. It is those specific to the various sound frequencies that respond.