The Thurimbar Rod is a musical instrument from Zilargo, which looks like a special metal wand. A Thurimbar Rod allows the musician to use illusion magic to mimic the sounds of any other instrument, and a skilled Thurimbarist can make one sound like a whole orchestra on their own. A musician using a Thurimbar Rod is limited only by their imagination and their magical skill.
The Thurimbar Rod is not iself magical, but helps to channel the user's magic, and so in the hands of someone without magical ability, it's just a stick. There are magical Thurimbar Rods however that amplify aspects of the illusory sound, such as amplifying it's volume or even creating visuals to accompany the music.