Piano Doctor - A Piano Tuner

This app analyzes piano sounds. It detects the frequencies in the sound and estimates how far the sound's tone is away from the target tone.

While detecting the middle and higher tones of a piano can be done with little difficulty, detecting lower tones such as A0 (27.5Hz) raises a challenge. This is because most mobile devices' microphones cannot pick up such low tones.

To overcome the difficulty, this app looks at two bands of frequencies: a fundamental band and a harmonic band. The fundamental band is the frequency range between -50 cents and +50 cents centered at the target frequency. Harmonic bands are the frequency bands where the frequencies are integer multiples of the fundamental band. This app examines 6 harmonic bands (from the second to the seventh) and selects the best one automatically.

Measuring the fundamental band allows users to detect middle and higher tones, while measuring the harmonic band allows users to detect lower tones.
By measuring the harmonic band as well as the fundamental band, this app can detect the entire range of piano tones from A0 to C8.

To graphically show the detected tones, two gauges are provided: one for the fundamental tone and another for the harmonic tone. Two spectrum viewers are also provided alongside the corresponding gauges. While gauges are good at showing peak tones, spectrum viewers are showing frequency spreads in two-dimensional shapes. Spectrums help identify which band's measurement is stabilized and ready to be read.

Buttons are used to select target pitch and octave quickly and randomly. Preset buttons are available for 7 preselected tones for easy-tone-selection and self-test. The preset buttons can also generate their corresponding tones through the device's speaker if they are double-clicked. This provides a self-test feature: with the self-generated tone on and the speaker at the proper volume, at least one of the gauges should report the precise tone that is being generated.