49 lines
2 KiB
Markdown
49 lines
2 KiB
Markdown
# SailTuner
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SailTuner is a chromatic multi-temperament instrument tuner for [Sailfish OS](https://sailfishos.org/).
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It gets audio data from microphone, find the fundamental frequency, and then display the note, the octave and the deviation according to note reference and temperament.
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It can also play a note, choosed with a scale flickable by user.
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### Pitch detection algorithm
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The algorithm for fundamental frequency detection:
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- high-pass filter (10Hz)
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- zero-crossing detection with linear interpolation
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- pattern recognition from regions, with time based standard deviation
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- octave filtering: drop a frequency if already a higher octave for same note in some conditions
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- post filter: wait few analyses to confirm or defect a note, and make a turning average for note deviation
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The audio input rate is 16KHz ; audio frames are analysed every 2048 samples (128ms) and a note is confirmed after 3 chunks (384ms).
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The note is found compared to an array of frequencies modulo one octave. The comparison array is built from a temperament and a 'A4' reference, default to 440Hz and equal temperament.
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### Temperaments
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The temperaments are stored in .csv files. At beginning, the programm scans every .csv file in the data/ dir and makes temperament list.
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Every line in a file is a temperament: the first column is the temperament name, and columns 2 to 13 are the notes frequencies from C-4 to B-4
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### Note player
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A frequency player module makes the signal at given frequency. There are 3 waveforms in the code:
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- Sinus
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- Triangle (ie pair harmonics)
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- Sinus + harmonics (1/n x f(n))
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Since the speaker of Jolla phone have very low intensity for low frequencies, the third solution is used, and the intensity is higher for lower notes.
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======
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### Copyright
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*Licence: GPLv3*
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*Author: Louis-Joseph Fournier*
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*First release date: 2016-01-19
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https://github.com/LouJo/SailTuner
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