Pitch Detection on Arduino using Autocorrelation

This is the last part of the article about the Arduino Pitch Detector.\(\)

Conclusion

I found that a sample rate of 9615 Hz and a window size of 200 samples combined with interpolation produce correct results for clarinet and piano from 155.6 Hz (Eb3) to 1568 Hz (G6).

On the clarinet, it misses the far lowest note (D3) and the very highest notes that only select musician can play (Ab6-B6) as shown in the visual. For clarinet, normalization only adds one low note to the range, while causing the frequency to be less accurate for high notes. As a result, I decided to not use normalization for clarinet.

For piano, I would use normalization because it adds an extra 7 low notes that would otherwise not be recognized. Things brings the piano range to 98 Hz (G2) to 1568 Hz (G6).

Segmentation works well at the cost of a slight delay which is noticeable but acceptable. Overall, I found that this project pushed the Arduino to its limits in both processing power and available memory.

To simplify things, I have undone the effect of transposing in processing the test results. The graph below illustrates this

own work
Clarinet, fs=9615Hz, N=200, with interpolation

Questions and problems that arose

The Arduino did not have enough memory to store the audio samples. Using fewer samples would cause low notes to be missed. Instead, I lowered the sampling rate so that there were fewer audio samples to store but caused the device to miss high notes. To improve the accuracy of these high notes, I used quadratic interpolation.

I minimized the delay by sampling the audio asynchronously and by limiting the autocorrelation algorithm to frequencies corresponding to the lowest and highest notes of the instrument.

To improve the range of notes recognized, I tried normalizing the autocorrelation for the zeroes introduced by the lag while shifting the waveform. For clarinet, normalization only added one low note while causing the frequency to be less accurate. As a result, I decided to not use normalization for clarinet. For piano on the other hand it would adds seven extra low notes.

Lessons learned

This was my first big project. It took many iterations to build something that I could be proud of. While some iterations made improvements, many were discouraging. However, reviewing these failures gave me valuable insights. I foremost learned to chose a project that I am truly passionate which made it easier to stick with. When problems arose, it helped to be patient.

In presenting my project, it worked best to start with a simple introduction and then answer questions. This allowed me to adjust to each person’s interests and background. I met judges who used the same algorithms as that I used in my project. Sharing insights with the judges at the Synopsis Silicon Valley and Technology Championship and the California State Science Fair was memorable.

In the future, I would make my project smaller and easier to handle. I would create an 1-inch round printed circuit board and would also use the Intel Curie SoC. This SoC can be programmed in a similar manner to the Arduino and includes a Bluetooth interface. This interface would allow me to eliminate wires. I also considered porting the code to Java to run on an Android phone, but I prefer to have a small device that can be clipped to the instrument.

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4 Replies to “Pitch Detection on Arduino using Autocorrelation”

  1. Hello,

    I want to know the frequency of the power grid, but harmonic frequencies in the power grid are a huge problem.
    Can you send me a code for ‘filtering’ fundamental? (0-150Hz max)
    Thanks!

  2. Hello,

    First of all, this a great work ! Not only just a sample stuff but very documented, you shoudl be proud !

    I’d like to use it for a guitare. Do you think it will work ? Did you test it ?

    Finally, did you make a video of it to see how good it works ? :)

    Thanks for the sharing and keep having fun making all these things :)

  3. Hello. Bravo for this work …
    I am a retired electronic engineer, and I designed a tuner working with FFT on a PC with a professional tool : Labview from National Instrument, which offers huge signal processing libraries. I wanted a very precise instrument to tune the reeds of a vintage italian accordion (Paolo Soprani, 1915). I am also playing bassoon, and then concerned with bass notes. I encountered many difficulties with low frequency cut off of the microphones, giving signals with harmonics far higher than fundamental (up to 20 dB). The lowest note of my accordion is a Bb at 58.27 Hz, on the left hand chords. This is also the lowest note of the basson. Precise measurement need very long sampling of several seconds !
    Well, now, I want to buid a little funny gadget which will animate a “snake” poping out of a basket in relation with the recognised notes … I am very interested by your work, but I think i will use a more powerfull processor than the Arduino uno, and then higher sampling frequency and 500 or 1000 samples.

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