Arduino Audio Tools – Resampling Revisited

So far I have provided some resampling functionality that was working with some integer factors to up- and downsample. After the work on the Pitch Shifting I realized that we can easily resample using a float based step size to achieve any resampling factor and determine the new values with the help of linear interpolation.

This is cool because we can now speed up or slow down the audio by any rate!
And the beauty of this: I could considerably reduce the code size and complexity of the implementation.

Example Arduino Sketch

#include "AudioTools.h"

uint16_t sample_rate=44100;
uint8_t channels = 1;                                      
SineWaveGenerator<int16_t> sineWave(32000);               
GeneratedSoundStream<int16_t> sound(sineWave);             
ResampleStream<int16_t> resample(sound);
CsvStream<int16_t> out(Serial); 
StreamCopy copier(out, resample);                        

// Arduino Setup
void setup(void) {  
  // Open Serial 
  Serial.begin(115200);
  AudioLogger::instance().begin(Serial, AudioLogger::Warning);

  // Setup sine wave
  sineWave.begin(channels, sample_rate, N_B4);

  // define resample
  auto resample_cfg = resample.defaultConfig();
  resample_cfg.step_size = 0.51;
  resample_cfg.channels = channels;
  resample.begin(resample_cfg); 

  // Define CSV Output
  auto config = out.defaultConfig();
  config.channels = channels;
  out.begin(config);
}

// Arduino loop - copy sound to out 
void loop() {
  copier.copy();
}

After the initialization you can change the rate at any time by calling resample.setStepSize(size). In the example above I am using the resampling on the input side, but we can also use it on the output side.

The Result

Here is the original output of the sine wave:

And this is the result of the resampling:

Jupyter

And last but not least here is a link to some resampling and mixing examples using Jupyter.