Passing planes and other whoosh sounds

I always assumed that the recognisable 'whoosh' sound a plane makes when passing overhead simply comes from the famous Doppler effect. But when you listen closely, this explanation doesn't make complete sense. (Audio clipped from freesound) A classic example of the Doppler effect is the sound of a passing ambulance constantly descending in pitch. When a plane flies overhead the roar of the engine sometimes does that as well. But you can also hear a wider, breathier noise that does something different: it's like the pitch goes down at first, but when the plane has passed us, the pitch goes up again. That's not how Doppler works! What's going on there? Comb filtering. Let's shed light on the mystery by taking a look at the sound in a time-frequency spectrogram. Here, time runs from top to bottom, frequencies from left (low) to right (high). We can clearly see one part of the sound sweeping from right to left, or from high to low frequencies; this should be the Doppler effect. But th ... Read full article.