When Guitar Guru is first started, the volume is set to the current setting of the master volume control in Windows. You can adjust the volume by clicking and dragging the pointer in the Volume Slider. Click the mute button 
to turn the sound on and off.
The overall volume can usually be adjusted several different ways depending on your computer. The volume range in Guitar Guru is equivalent to the volume range of the master volume control in Windows. You may be able to obtain different volume levels by adjusting the Windows volume controls SW Synth (for MIDI audio), Wav (for CD audio), or the volume control of your speakers.