What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?

when observer and source moves relative to each other then the frequency received by the observer is different from the real frequency

This apparent change in frequency due to relative motion is known as Doppler's effect.

Here we know that

here we know that

= real frequency

v = speed of sound

= speed of observer

= speed of source

so this is known as Doppler's Effect