Hermann von Helmholtz said that one hears different pitches because different sound waves trigger activity at different places along the cochlea basilar membrane. His theory is called theory.

Place theory

Explanation:

 The place theory is one of the type of hearing based process that helps in distinguish between the high or the low pitched sounds and in the range of the frequency.

The main objective of the place theory is that the person can easily hear the different pitches because of the sound frequency which typically cause the vibration in the specific membrane cochlea part in our hear.

 According to the given question, the place theory is developed by the Hermann von Helmholtz and he explained that the person can easily hear the different pitches due to the differ in the sound waves in the membrane.    

 Therefore, Place theory is the correct answer.

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