Whatever my neighbors’ kid is playing. I’m in a townhouse. I don’t understand how the old folks on the other side tolerate it. As for me, it must be my penance. I used to do the same thing, not realizing that the neighbors can likely hear it. The older wiser me knows that a 6” concrete firewall does little in the way of sound attenuation.
I did it and I knew my neighbours would hear it. At that time I had a DIY-transmission line designed by a sound Ingenieur called Klinger with kef bass chassis, that had the deepest bass - down to almost 25 Hertz - I’ve ever heard until today. Once I met my neighbour in the university canteen. He asked me how I am improving my play on the double bass, I obviously played whole day long.
He was a little bit offended as I told him, that it was probably Charlie Haden he had heard from a recording.
And worse, he claimed my further listening every time with knocking on the floor. Suddenly I obviously lost the status of being a musical genius, a picture that he kept up for a long time.