Guitar string vibrating. When plucked, the string vibrates at a specific frequency, which determines the pitch of the note. The vertical lines on the fretboard (centre right) of the guitar mark where fingers should be placed to shorten or lengthen the vibrating part of the string. Shortening the string produces a note with a higher pitch, lengthening it lowers the note. The vibration of the string itself does not create much sound, but the strings in turn cause the top plate of the guitar to vibrate, which is much louder. The hole at centre left allows these amplified sound waves to escape.