There are several options available in Settings → Game tab and here are some of the most common ones.
Volume: Adjust volume levels in the game on the desktop app by dragging it left to decrease volume or right to increase volume.
Sound effects: Adjust the volume of sound effects in app.
Audio setup: Advanced settings
Input channel: Choose input channel (input 1 or 2); Supported audio interfaces are automatically recognized and set as default;
Buffer size: Smaller buffer will decrease audio latency, but it may cause performance issues or audio glitches. Larger buffer will have longer audio latency, but better performance.
Automatic MIDI input (available only if curriculum is set to piano): In order to use your MIDI keyboard, make sure that the ‘Automatic MIDI Input’ toggle is active. If the piano sound is delayed, set the buffer size to 256 or lower.
Song data cache: You can clear cached songs here. This is recommended especially if you are having trouble loading songs on your device.
Resolution (desktop only): Adjust the app window to your screen.
Fullscreen (desktop only): Switch to the full screen view mode.
Pre-song chord trainers (guitar & ukulele): Toggle on to rehearse chords before starting to play a song.
Note duration feedback: Toggle on and become more aware of note duration both in background music and in your own playing. Check level 2 guitar mission in Lead called Fretboard Workout to see the feature in action.
Left-handed mode: Toggle on for left handed players.
Colorblind mode: Change the game play colors; current available themes are Protanopia, Deuteranopia and Tritanopia.
Today's goal achievement screen: Toggle off to stop Daily goal updates.