Simple Frequency Detection

Audio frequency detection is the process of identifying the pitch or dominant frequency of a sound signal. Three common methods used are Fast Fourier Transform (FFT), AutoCorrelation, and Zero-Crossing.

• AutoCorrelation compares a signal with delayed versions of itself to detect repeating patterns, which correspond to pitch. It's effective for monophonic signals and works well in noisy environments, but can be computationally intensive.

• Zero-Crossing counts how often the signal crosses the zero amplitude axis to estimate frequency. It is simple and fast but only reliable for clean, single-frequency signals and can be inaccurate with harmonics or noise.

• FFT transforms a time-domain audio signal into its frequency components, making it ideal for identifying multiple frequencies or spectral content. It's accurate for complex signals but may require windowing and smoothing for real-time pitch tracking.

This chapter describes how to do the more lightweight AutoCorrelation and Zero-Crossing. Here is a simple example:

#include "AudioTools.h"

AudioInfo info(44100, 2, 16);
SineWaveGenerator<int16_t> sineWave;
GeneratedSoundStream<int16_t> sound(sineWave);
FrequencyDetectorAutoCorrelation out(1024);
// FrequencyDetectorAutoCorrelation out;
StreamCopy copier(out, sound, 10 * 1024);

// Arduino Setup
void setup(void) {
  // Open Serial
  Serial.begin(115200);

  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Warning);

  // start I2S
  Serial.println("starting ...");
  out.begin(info);

  // Setup sine wave
  sineWave.begin(info, 200);
  Serial.println("started...");
}

// Arduino loop - copy sound to out
void loop() {
  copier.copy();
  Serial.print(out.frequency(0));
  Serial.print(" ");
  Serial.println(out.frequency(1));
}