improved support for PDM microphones (SPM1423)

seems that the "swapped channel" workaround is not needed for PDM.

Author: softhack007

usermods/audioreactive/audio_reactive.h

@@ -1149,7 +1149,7 @@ class AudioReactive : public Usermod {
         #if  !defined(CONFIG_IDF_TARGET_ESP32S2) && !defined(CONFIG_IDF_TARGET_ESP32C3)
         case 5:
           DEBUGSR_PRINT(F("AR: I2S PDM Microphone - ")); DEBUGSR_PRINTLN(F(I2S_MIC_CHANNEL_TEXT));
-          audioSource = new I2SSource(SAMPLE_RATE, BLOCK_SIZE);
+          audioSource = new I2SSource(SAMPLE_RATE, BLOCK_SIZE, true, 1.0f/4.0f);
           delay(100);
           if (audioSource) audioSource->initialize(i2swsPin, i2ssdPin);
           break;

usermods/audioreactive/audio_source.h

@@ -201,11 +201,20 @@ class I2SSource : public AudioSource {
           return;
         }
       } else {
+        #if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(4, 2, 0)
+          #if !defined(SOC_I2S_SUPPORTS_PDM_RX)
+          #warning this MCU does not support PDM microphones
+          #endif
+        #endif
         #if !defined(CONFIG_IDF_TARGET_ESP32S2) && !defined(CONFIG_IDF_TARGET_ESP32C3)
+        // example from espressif: https://github.com/espressif/esp-idf/blob/release/v4.4/examples/peripherals/i2s/i2s_audio_recorder_sdcard/main/i2s_recorder_main.c
         // This is an I2S PDM microphone, these microphones only use a clock and
         // data line, to make it simpler to debug, use the WS pin as CLK and SD
         // pin as DATA
         _config.mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_PDM); // Change mode to pdm if clock pin not provided. PDM is not supported on ESP32-S2. PDM RX not supported on ESP32-C3
+        _config.channel_format =I2S_CHANNEL_FMT_ONLY_LEFT;                       // seems that PDM mono mode always uses left channel.
+        //_config.use_apll = true;                                                 // experimental - use aPLL clock source to improve sampling quality
+        //_config.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT;                     // not needed
         #endif
       }
 
@@ -249,9 +258,11 @@ class I2SSource : public AudioSource {
 
       DEBUGSR_PRINTF("AR: I2S#0 driver %s aPLL; fixed_mclk=%d.\n", _config.use_apll? "uses":"without", _config.fixed_mclk);
       DEBUGSR_PRINTF("AR: Sample scaling factor = %6.4f\n", _sampleScale);
-      if(_config.mode & I2S_MODE_MASTER) 
-        DEBUGSR_PRINTLN(F("AR: I2S#0 driver installed in MASTER mode."));
-      else
+      if(_config.mode & I2S_MODE_MASTER) {
+        if (_config.mode & I2S_MODE_PDM)
+          DEBUGSR_PRINTLN(F("AR: I2S#0 driver installed in PDM MASTER mode."));
+        else DEBUGSR_PRINTLN(F("AR: I2S#0 driver installed in MASTER mode."));
+      } else
         DEBUGSR_PRINTLN(F("AR: I2S#0 driver installed in SLAVE mode."));
 
       err = i2s_set_pin(I2S_NUM_0, &_pinConfig);