Consider investing a lot of building efficiency into the recorder if you will not always be playing actively. The recorder generates notes for you, however it has a limit that depends on how well it has been upgraded. Collect your earnings regularly to avoid losing them. Displayed under your total notes is a red number that indicates your "building efficiency". This corresponds to how many notes your buildings can generate per second. A higher number is better. To increase it, upgrade your buildings. Each building you have increases the building efficiency. You can view how much each type of building earns by looking next to it in the "Building" menu. Upgrade everything equally to keep your building efficiency high.