How to connect 4 microphones and hear the voice at the same time?

[XY]

I am trying to monitor the human heartbeat by using a microphone array. But there got some problems. Channels A and B work fine but channels C and D do not work. I don't know why this is happening. I am using the "through" example of the Arduino IDE.

[CamilaSouza]

Hi @XY

How are you connecting the microphones?
Please share your code so we can take a look at it.

[XY]

@CamilaSouza
Hi
this is my code

#include <Audio.h>

AudioClass *theAudio;

/**
 * @brief Audio attention callback
 *
 * When audio internal error occurc, this function will be called back.
 */

static void audio_attention_cb(const ErrorAttentionParam *atprm)
{
  puts("Attention!");
  
  if (atprm->error_code >= AS_ATTENTION_CODE_WARNING)
    {
      exit(1);
   }
}

/**
 * @brief Setup audio through to I2s input to speaker
 *
 * Set output device to speaker <br>
 * Set input mic gain to 16.0 dB
 */
void setup()
{

  /* start audio system */
  theAudio = AudioClass::getInstance();
  theAudio->begin(audio_attention_cb);

  puts("initialization Audio Library");

  /* Set input source with first argument.
   * The second argument means source of I2s output.
   * If you set "I2sIn" as the first argument, please set "None" as the second argument.
   * Set speaker driver mode to LineOut with last argument.
   * If you want to change the speaker driver mode to other,
   * specify "AS_SP_DRV_MODE_1DRIVER" or "AS_SP_DRV_MODE_2DRIVER"
   * or "AS_SP_DRV_MODE_4DRIVER" as an argument.
   *
   */
  int err = theAudio->setThroughMode(AudioClass::MicIn, AudioClass::None, true, 160, AS_SP_DRV_MODE_LINEOUT);
  if (err != AUDIOLIB_ECODE_OK)
    {
      printf("Through initialize error\n");
      exit(1);
    }

  theAudio->setVolume(-160);
  if (err != AUDIOLIB_ECODE_OK)
    {
      printf("Set Volume error\n");
      exit(1);
    }
}

[XY]

@CamilaSouza
Regarding the connection of the microphones, I used four analogue microphones, connected to the JP10 according to the connection on the official website. Since all four mics work on channels A and B, I think there is no problem with the connection method.

[CamilaSouza]

Hey @XY

After some investigation:

Through sends the sound from microphone directly to speaker. And speaker has just 2 channels: Left and Right.
So the behavior you are experiencing is the normal one. Ch A sends to left channel and Ch B sends it to right channel.

If you want to listen to the 4 channels there are two ways.
One is to save it in wav file. WAV format can support 4 channels in one file. 
The other is software mixer. 4 channels data is coming as Ch1, Ch2, Ch3, Ch4, Ch1, Ch2, Ch3, Ch4..... So you can make a kind of audio mixer to mix Ch1 and Ch2, Ch3 and Ch4, and then, output to speaker as Left Right channel.