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 device: Allows you to choose the input device used for recognition. Inbuilt microphone in the device used is automatically chosen as default, unless the instrument is connected using an audio interface.
Input channel: Choose input channel (input 1 or 2); Supported audio interfaces are automatically recognized and set as default;
Buffer size: This setting is available on iOS and Android versions. 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.
MIDI sensitivity: (available if a keyboard is connected to the device used): Some keyboards have the ability to perceive how hard/soft a key is played; the more strength used the louder the sound produced. With higher sensitivity chosen, Yousician is able to recognize this and produces the Midi sound accordingly. If using a mobile device and 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.
Fullscreen (desktop only): Although you can adjust the screen size by simply dragging it with your mouse, you can also switch to full screen view mode by toggling the option on.
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.