This Web application finds musical themes from the renaissance-barock-rococo-classical-romantic period.
Use mouseclicks on the pianokeyboard or keys (q w e r t y etc.) to play or "indicate" the beginning of the theme you are searching.
The first 5-10 notes of the theme are usually sufficient
Don't worry about playing in the correct key
Don't worry about tempo and note lengths
Disregard graces like trills, mordents, etc.
Your input needs not be accurate and error free
Remember that this application currently only finds themes by composers born prior to 1840
To find Bachs "Jesu, Joy of Man's Desiring", you could type/click the first 7 notes q w e t r r y and hit Enter/OK! If you type less notes, you will get other matches as well. If you type more, you will still find the cantata by Bach.