In this exercise, you'll hear two tones. First, the fundamental, and later, an overtone. Your task is to identify which overtone you're hearing by clicking on the corresponding wave. In other words, how many times is the frequency of the first tone multiplied to match the second tone?

This exercise is similar to interval training, but it's different. Instead of training your ears to recognize musical intervals as defined by twelve-tone equal temperament, this exercise instead challenges you to recognize tones as parts of the harmonic series, which is based on multiplying a frequency by whole numbers.

If you get bored of guessing harmonics compared to a fundamental frequency, you can enable hard mode, in which the first tone you hear will not be the fundamental, but rather, a random harmonic. This means you must determine the interval between the two tones as a ratio of whole numbers (or a justly intonated interval), when the fundamental is not given.

Note: if you want the fundamental frequency to remain the same, just set the minimum frequency to any number and set the range to 0.

Note: If you hear no sound, try headphones! Pure sine waves won't make it through your phone speakers (especially if you have the frequency parameters set very low).