Processing and Transmitting Filtered I2S Microphone Data via BLE

[MichalisChachalios]

I have successfully interfaced an I2S microphone with my microcontroller, applied low-pass filters to the captured data, and visualized the results using the serial monitor. I am now looking to further process this data by transmitting it over Bluetooth Low Energy (BLE).

Specifically, I have two main objectives:

Accessing and Manipulating the Audio Stream: I am utilizing the Copy class to handle the audio data flow. Could you provide guidance on how to intercept and process this stream before outputting it? For instance, I aim to calculate the amplitude of the filtered audio data prior to transmission, and save it in a float variable, that I would like to transmit via BLE.

Transmitting Audio Data via BLE: Is it feasible to send the processed audio data over BLE to another ESP32 device? If so, could you recommend any existing functionalities within the Arduino Audio Tools library or related examples that facilitate this?

This is the code I used so far:

/**
 * @file streams-i2s-filter-i2s.ino
 * @brief Copy audio from I2S to Serial using an FIR filter
 * @author Phil Schatzmann
 * @copyright GPLv3
 */

#include "AudioTools.h"
 
AudioInfo info(44100, 1, 16);
I2SStream in;


// copy filtered values
FilteredStream<int16_t, float> filtered(in, info.channels);  // Defiles the filter as BaseConverter

CsvOutput<int32_t> csvStream(Serial);
StreamCopy copier(csvStream, in); // copy i2sStream to csvStream


// define FIR filter parameters
float coef[] = { 0.021, 0.096, 0.146, 0.096, 0.021};


// Arduino Setup
void setup(void) {  
  // Open Serial 
  Serial.begin(115200);
  // change to Warning to improve the quality
  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info); 

  // setup filters for all available channels
  filtered.setFilter(0, new FIR<float>(coef));
  // filtered.setFilter(1, new FIR<float>(coef));

  // start I2S in
  Serial.println("starting I2S...");
  auto config_in = in.defaultConfig(RX_MODE);
  config_in.copyFrom(info); 
  config_in.i2s_format = I2S_STD_FORMAT;
  config_in.is_master = true;
  config_in.port_no = 0;
  config_in.pin_ws = 14;
  config_in.pin_bck = 15;
  config_in.pin_data = 16;
  // config_in.fixed_mclk = sample_rate * 256
  // config_in.pin_mck = 3

  in.begin(config_in);

  // make sure that we have the correct channels set up
  csvStream.begin(info);

  Serial.println("I2S started...");
}

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

[pschatzmann]

It should be possible to transmit Audio over BLE between 2 ESP32 devices.
Have a look at the ble examples in the Sandbox directory

[MichalisChachalios]

Thanks for your really quick response. Can you also help me understand how to access the actual data of the stream ? The simplest application would be to plot the values in the Teleplot app of the VScode, via PlatformIO. In order to do that the Serial plotter should have the format ">name:" + value

[pschatzmann]

You would just replace the I2SStream with a CsvOutput.
Please note that your sketch has an ugly bug: if you use 16 bits in AudioInfo the CSVStream must be 16 bits as well and not 32!