When checked, Default device and Default input selections are disabled. To enable them, uncheck the box.

If your computer has more than one sound devices installed, you can select the Default device.

The recording devices usually have several inputs. The input names depend on the device. Typical inputs include Line-in, Microphone, etc.

Both the device and its input are displayed in Default device box. As a result, Default input box simply shows Master Volume.

This button opens a Windows system Sound. To control the recording input volume levels, click Properties button. Then the properties dialog box of current device appears. Select Levels tab, and adjust the levels. (For more info, follow the above OS links.)

If your computer has more than one sound devices installed, you can select the Default device.

This button opens a Windows system Volume Mixer. You can use it to control the playback volume levels.