What does it sound like when an ambulance with it's sirens on is not in motion& an object ismoving towards it?

i know about the doppler effect and the wave lengths when the ambulance is coming towards you or away from you but what about when it's stationary and another object is moving towards it or away from it? how does it sound and what is it's pitch?What does it sound like when an ambulance with it's sirens on is not in motion%26amp; an object ismoving towards it?
Great question!





Although this is rarely explained, the Doppler effect works even when the object emitting the sound waves is stationary! If you are moving towards the object at a constant speed, the sound, in this case the ambulance's sirens will be higher-pitched than normal.





When you pass it and start moving away, they will suddenly become lower-pitched.





What matters here is relative velocity. If there you and the object are moving apart or together -at any speed-, you will perceive the sound waves to be compressed or elongated, and you will hear an altered sound.