[playback] Secondary voices: lower velocity/dynamics by default
All voices which are not Voice 1 could be lower in velocity by default. I think one should want this in 99% of the case. In case this is not wanted, the user could disable this with some given option.
If the user wants more complexity, then he/she will manually select the other voices and input the wanted velocity values by itself. But it would be neat to have at least voice 1 standing out by default.