  We introduce Purrfect Pitch, a system consisting of a wearable haptic device
and a custom-designed learning interface for musical ear training. We focus on
the ability to identify musical intervals (sequences of two musical notes),
which is a perceptually ambiguous task that usually requires strenuous rote
training. With our system, the user would hear a sequence of two tones while
simultaneously receiving two corresponding vibrotactile stimuli on the back.
Providing haptic feedback along the back makes the auditory distance between
the two tones more salient, and the back-worn design is comfortable and
unobtrusive. During training, the user receives multi-sensory feedback from our
system and inputs their guessed interval value on our web-based learning
interface. They see a green (otherwise red) screen for a correct guess with the
correct interval value. Our study with 18 participants shows that our system
enables novice learners to identify intervals more accurately and consistently
than those who only received audio feedback, even after the haptic feedback is
removed. We also share further insights on how to design a multisensory
learning system.
