This app implements an audio filter around any selected pitch from C2 to C8. The sound from the microphone is filtered according to parameters set by the user and played back to the user, preferably over a headset. The app features a selectable filter bandwidth from 400 cents to 30 cents. The purpose of this filter is to help in training aural piano tuners. When playing an interval, the aural tuner needs to be able to focus on a coincident partial of the two notes to assess the beat rate at that partial. If this filter is set to isolate that coincident partial then the job of picking out the desired pitch is easier. Once the user has learned to focus on coincident partials this filter will not be necessary. This is a training tool, not a tool for everyday use.

In addition to the filtering function this app also provides a synthesizer function that synthesizes a pure tone beating at a user-specified rate. The purpose of this synthesizer is for training aural piano tuners to recognize beat rates. The synthesized beat rates can be set from 1/10 beat per second to 30 beats per second. The beat rates of these "rapidly beating intervals" are especially difficult to assess when they are too fast to count. By listening to a synthesized beat at a specified beat rate the user can develop a sense of recognizing that beat rate in an interval played on the piano.