volume
The option documentation is properly formatted yet
Description: "Main Volume" Default: 100 Example: 50 Type: integer Range: 0 - 100 Since: 2.3.8
Use this setting to specify a lower volume than the default 100%. You can change the volume while using the emulator with keyboard shortcut keys.
Source: https://github.com/FrodeSolheim/fs-uae/blob/master/docs/options/volume