How do I compare pitch apps?

A number of apps in the App Store report frequency measurements. What is the difference between them?

Instrument Tuning Apps

This class of apps is designed to help tune musical instruments, particularly guitars. Because instruments produce a clear tone at a specific note, it is quite easy to measure the frequency of that note from a peak in the sound spectrum. The human voice is much more complex. Often, the peak frequency of a human voice corresponds to a "harmonic", and not to the "fundamental" frequency or pitch that we would like to measure. This means that the instrument tuning apps may often be off by a factor of two or more for some types of voices. Sonneta Voice Monitor is designed specifically to ignore harmonics and measure the true fundamental frequency.

Singers' Apps

This class of apps measures pitch in order to tell singers whether they are on key. Trained voices are like musical instruments in that they focus most of their energy at specific notes. Apps designed for singing can have trouble measuring running speech or voices with dysphonia (voice disorders) or with glottal fry (creakiness). Sonneta Voice Monitor is designed to provide a robust measurement of both normal and dysphonic voices. It compares favorably with dedicated workstations costing thousands of dollars.

Things to Check

When comparing pitch measurement software, here are some things you might want to check: