You get this in the fourth level by playing the right music for each of the 3 mask people.
Once you have all of the raspberry-ified fuzzies, they have 3 heights of music each. The right patterns are:
Sad - 1, 3, 2, 3
Happy - 3, 1, 1, 2
Disco - 2, 2, 3, 1
After you match the 3rd one you'll get the achievement!
