The Hinterhof from my 3rd floor window. Monday, 3 days after Covid-19 restrictions

The Hinterhof is eerily quiet. It's as if many of those living here don't exist. Maybe they've gone away. I'm not hearing children any more. This tone is often present and sounds no different from always (it is an accidental wind flute from one of the external pipes from the heating system) but it's detail is more apparent with less urban rumble. There's a slightly harmonic hiss associated with it hasn't been clear till now. Also the city's sub bass is more audible. Interesting which sounds are revealed when normal acoustic backdrop changes. There also more sirens, presumably ambulances.