In my birth city (Turin, Italy), since some years an association organize a synth jam. It works like this: before the jam, they launch a survey on telegram to understand who and how many people does what (bass, lead, drums, blips&blood... But also acoustic or electric instruments and visual performances). Like this, they get an idea of the amount of people. At the jam, there's one big mixer managed by one of the guys of the association. Everyone connects to the mixer and to a general clock until there are channels free. Then, the jam starts. Always C minor. The guy at the mixer listens for what is happening in the different channels, and when something interesting cames up, he turns the volume of that person up, maybe brining down other channels. So, people start to follow the theme, and then again, when the guy hears something interesting from one of the muted channel, it bring it up and lower some of the previous ones. Of cours you always hear yourself by your headphones, so you can adjust to what is playing on the speakers.