How to use PDM mic properly?

[yujonglee]

I saw in 2174cec , example about PDM mic is added.

I have some question:

1. What is cfg.signal_type = PDM for? I searched the codebase but signal_type seems to do nothing.

2. arduino-audio-tools/examples/examples-stream/streams-i2s_pdm-serial/streams-i2s_pdm-serial.ino

   Line 29 in 33018b1

   cfg.pin_bck = I2S_PIN_NO_CHANGE; // not used

   Can you explain what does not used mean here?
   In the ESP doc said I need CLK and DATA, and I thought .pin_bck is corresponding to CLK.
3. If I use two PDM mic connected, (select pin of one is high and other is low) what I2S format should I use instead of I2S_CHANNEL_FMT_ALL_RIGHT in example?

enum I2SFormat {
  I2S_STD_FORMAT,
  I2S_LSB_FORMAT,
  I2S_MSB_FORMAT,
  I2S_PHILIPS_FORMAT,
  I2S_RIGHT_JUSTIFIED_FORMAT,
  I2S_LEFT_JUSTIFIED_FORMAT,
  I2S_PCM,
};

Thank you.

[pschatzmann]

I suggest that you read the documentation or just use the corresponding example

[yujonglee]

@pschatzmann Thanks. I got it. CLK is corresponding to pin_ws.

Just one thing: How about I2SFormat that I mentioned in 3?

arduino-audio-tools/src/AudioI2S/I2SESP32-New.h

Line 113 in 33018b1

struct DriverI2S : public DriverCommon {

arduino-audio-tools/src/AudioI2S/I2SESP32-New.h

Line 202 in 33018b1

struct DriverPDM : public DriverCommon {

Seems like when using PDM, I2SFormat does not matter but just wanna classify.

Thank you.

[pschatzmann]

That would be my understanding as well: just notice that the new Driver is only available when you use the latest IDF versions.
In Arduino the old I2S API is used...