This is a simple, ad-free instrument tuning Android app.
Here's a brief overview of how it works:
- Compute the autocorrelation of the audio signal. This should give a periodic plot with peaks where the signal perfectly overlaps with itself.
- Determine the period by computing the zero crossings. The actual implementation is via a grid search over some offset values.
- Compute the mean and standard deviation of the observed period and update a Kalman filter that gives a smoothed estimate of the period.
- Find the closest musical pitch in the 12-tone equal temperament system and compute the error in frequency and cents.
- Update the frame of the tuner graphic as a function of the error in cents.
The Simple Tuner app requires the use of your device's microphone to record audio. This audio data is not persisted in any permanent storage and is processed on your device. No other personally identifiable information is used by the Simple Tuner app.
This project is covered by the GNU General Public License v3. See the LICENSE file.