The ESP32 I2S 24 bit Mystery

I had the issue that the 24 bit output via A2DP was not working, but the corresponding 32 bit example was just working fine.

So I decided to double check the I2S output with the help of a logical analyzer.

Checking 16 bits

First I was double checking how the working 16 bit is showing up. So I used the following Arduino Sketch which was just outputting some unique numbers per byte:

#include "AudioTools.h"

AudioInfo info{44100, 2, 16};
I2SStream i2s;
uint8_t data[] = {0x01,0x02,0x03,0x04};

void setup() {
  auto cfg = i2s.defaultConfig(TX_MODE);
  cfg.copyFrom(info);
  i2s.begin(cfg);

}

void loop() {
  i2s.write(data, sizeof(data));
}

This is showing up in PulseView as follows, with the byte sequence reversed:

Checking 24 bits

So it is time now to check the output of 24 bits:

#include "AudioTools.h"

AudioInfo info{44100, 2, 24};
I2SStream i2s;
uint8_t data[] = {0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08};

void setup() {
  auto cfg = i2s.defaultConfig(TX_MODE);
  cfg.copyFrom(info);
  i2s.begin(cfg);

}

void loop() {
  i2s.write(data, sizeof(data));
}

So as indicated in the documentation, the least significant (and in this case the first) byte gets ignored:

So this is working as expected.

Further Tests

Then I executed the test with a 24 bit sine tone and one with a 16 bit sine, that gets converted to 24 bits. All w/o any issues: so there is no problem in my 24 bit functionality in the AudioTools and it is working properly.

But it still remains a mistery to me why the very same thing generated from A2DP is not working and generates noise. This does not make any sense!