Let the sound frequency be v and the speed be v; The moving speed of the receiver is U, which is positive when it is close to the sound source and negative when it is far away from the sound source.

According to the Doppler effect formula V'= V(V+U)/V

The speed of sound can be obtained as V=U/(v'/v- 1)=Uv/(v'-v).

When the receiver moves faster than the speed of sound, there are two situations:

(1) When the receiver is close to the sound source, the moving speed is u >: V, and the frequency is greatly increased, but the above formula can still be used directly;

(2) When the receiver is far away from the sound source, the moving speed u

v = U/(-| v ' |/v- 1)= Uv/(-| v ' |-v)= | U | v/(| v ' |+v)。

Supplement: There is something wrong with the answer of Harbor4 1, which is faster than the speed of sound. It just leaves the sound wave behind, but it can still catch up with the sound wave in front, thus measuring the corresponding frequency, and the unexpected sound will not be unreadable.