# How to refer to the built in microphone?

**URL:** <https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606>\
**Category:** Audio\
**Created:** [July 2, 2024, 2:08pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606 "2024-07-02T14:08:04Z")\
**Posts on this page:** 13\
**Page:** 2

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**Author:** ![murosic](https://avatars.discourse-cdn.com/v4/letter/m/848f3c/32.png) [@murosic](https://forum.arduino.cc/u/murosic)\
**Post date:** [July 15, 2024, 1:50pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/22 "2024-07-15T13:50:00Z")

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@noweare This is very handy to know for the next phase, thank you!

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<div class="post-metadata">

**Author:** ![murosic](https://avatars.discourse-cdn.com/v4/letter/m/848f3c/32.png) [@murosic](https://forum.arduino.cc/u/murosic)\
**Post date:** [July 15, 2024, 2:21pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/23 "2024-07-15T14:21:06Z")

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@rsmls I don't understand how to implement this concept. The basic principle is that a state is changed based on the input, but there is input continuously. Or do you mean I should give one function the lead and run it when needed, and only run the other function when the lead function isn't running?

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<div class="post-metadata">

**Author:** ![anon94801460](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@anon94801460](https://forum.arduino.cc/u/anon94801460)\
**Post date:** [July 15, 2024, 2:23pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/24 "2024-07-15T14:23:38Z")

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> [@murosic](#):
>
> The basic principle is that a state is changed based on the input, but there is input continuously

Why do you think that is a problem?

Read input(s), make state change decisions.

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<div class="post-metadata">

**Author:** ![murosic](https://avatars.discourse-cdn.com/v4/letter/m/848f3c/32.png) [@murosic](https://forum.arduino.cc/u/murosic)\
**Post date:** [July 15, 2024, 2:42pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/25 "2024-07-15T14:42:30Z")

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So I have this now. At least there is data coming in, only it doesn't look like audio data.

Current code:

```arduino
// Main tab =======================================================--
#include <PDM.h>
#include <Arduino_HS300x.h>
#include <SD.h>
#include <SPI.h>

float temperature;
float humidity;

void setup() {
  Serial.begin(9600);
  while (!Serial);
  PDM.setBufferSize(2048); //bytes!

initializeSDCard();

  if (!HS300x.begin()) {
    Serial.println("Failed to initialize humidity temperature sensor!");
    while (1);
  }
}

void loop() {
  Serial.println("run loop");
  temperature = HS300x.readTemperature();
  humidity = HS300x.readHumidity();
  recordAudio();
  delay(99999999);
}

// Record audio tab =================================================

// Define constants
const int sampleRate = 16000;
const int sampleBufferSize = 8192;

// Declare buffers
int16_t sampleBuffer[sampleBufferSize];
uint8_t cpBuffer[sampleBufferSize * 2]; // 2 bytes per sample
volatile int audioSamplesRead = 0;
volatile int totalAudioSamplesRead = 0;

void recordAudio() {
  Serial.println("Try to record audio");
  totalAudioSamplesRead = 0;

  PDM.onReceive(onPDMdata);
  if (!PDM.begin(1, sampleRate)) {
    Serial.println("Failed to start PDM!");
    while (1);
  } else {
    Serial.println("PDM started successfully.");
  }

  while (totalAudioSamplesRead < 8000) {
    if (audioSamplesRead > 0) {
      Serial.print("TotalAudioSamplesRead: ");
      Serial.println(totalAudioSamplesRead);
      Serial.print("AudioSamplesRead: ");
      Serial.println(audioSamplesRead);

      for (int i = 0; i < audioSamplesRead; i++) {
        cpBuffer[2 * i] = (sampleBuffer[i] >> 8) & 0xFF;
        cpBuffer[2 * i + 1] = sampleBuffer[i] & 0xFF;
      }

      totalAudioSamplesRead += audioSamplesRead;
      audioSamplesRead = 0;
    }
  }
  PDM.end();
  processAudio();
}

void onPDMdata() {
  // Query the number of bytes available
  int bytesAvailable = PDM.available();

  // Read into the sample buffer
  PDM.read(sampleBuffer, bytesAvailable);

  // Update the number of samples read
  audioSamplesRead = bytesAvailable / 2; // 16-bit, 2 bytes per sample
}

void processAudio(){
  sendValues();
}

// Send values tab ================================================

void sendValues(){
  Serial.println("Sending values...");
  Serial.print("Temperature: ");
  Serial.println(temperature);
  Serial.print("Humidity: ");
  Serial.println(humidity);
  Serial.println("Audio 16 bit: ");
  for (int i = 0; i < sizeof(sampleBuffer);i++){
    Serial.print(" ");
    Serial.print(sampleBuffer[i]);
  }
  Serial.println("");
  Serial.println("Audio 8 bit: ");
  for (int i = 0; i < sizeof(cpBuffer);i++){
    Serial.print(" ");
    Serial.print(cpBuffer[i]);
  }
  Serial.println();
}

// Functions tab =================================================

void initializeSDCard(){
  #define SD_CSPin 10

  int file_number = 0;
  char filePrefixname[50] = "buzz";
  char exten[10] = ".wav";

  Serial.println("loading... SD card");
  if (!SD.begin(SD_CSPin)) {
            Serial.println("An Error has occurred while mounting SD");
  }
  while (!SD.begin(SD_CSPin)) {
            Serial.print(".");
            delay(500);
  }
}

```

Output:

```arduino
16:36:24.358 -> AudioSamplesRead: 1024
16:36:24.425 -> TotalAudioSamplesRead: 2048
16:36:24.425 -> AudioSamplesRead: 1024
16:36:24.518 -> TotalAudioSamplesRead: 3072
16:36:24.518 -> AudioSamplesRead: 1024
16:36:24.553 -> TotalAudioSamplesRead: 4096
16:36:24.553 -> AudioSamplesRead: 1024
16:36:24.619 -> TotalAudioSamplesRead: 5120
16:36:24.619 -> AudioSamplesRead: 1024
16:36:24.702 -> TotalAudioSamplesRead: 6144
16:36:24.702 -> AudioSamplesRead: 1024
16:36:24.742 -> TotalAudioSamplesRead: 7168
16:36:24.773 -> AudioSamplesRead: 1024
16:36:24.773 -> Sending values...
16:36:24.773 -> Temperature: 25.57
16:36:24.773 -> Humidity: 56.85
16:36:24.773 -> Audio 16 bit: 
16:36:24.773 -> 298 305 296 286 291 304 301 296 298 295 295 298 303 293 290 ...
16:36:28.521 -> Audio 8 bit: 
16:36:28.521 -> 1 42 1 49 1 40 1 30 1 35 1 48 1 45 1 40 1 42 1 39 1 39 1 42 1 ...

```

The 16 bit (source for 8 bit) audio has strange values; the 8192 samples can be divided in these groups:

- The first part contains samples that are pretty stable around 330, slowly decreasing to around 70
- The middle part contains mainly zeros with here and there a small bunch of other samples
- The last part contains only value -13108

When I reset the Arduino I get approximately the same over and over. When I run the example code called PDMSerialPlotter, I get audio-like values from around -40 to 40 that increase when I make noise, so the mic seems to work fine. Any ideas how to get real audio data?

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<div class="post-metadata">

**Author:** ![anon94801460](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@anon94801460](https://forum.arduino.cc/u/anon94801460)\
**Post date:** [July 15, 2024, 2:49pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/26 "2024-07-15T14:49:42Z")

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> [@murosic](#):
>
> ```arduino
> for (int i = 0; i < audioSamplesRead; i++) {
> cpBuffer[2 * i] = (sampleBuffer[i] >> 8) & 0xFF;
> cpBuffer[2 * i + 1] = sampleBuffer[i] & 0xFF;
> }
> 
> ```

What is the above supposed to be doing, and why?

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<div class="post-metadata">

**Author:** ![murosic](https://avatars.discourse-cdn.com/v4/letter/m/848f3c/32.png) [@murosic](https://forum.arduino.cc/u/murosic)\
**Post date:** [July 15, 2024, 2:52pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/27 "2024-07-15T14:52:05Z")

</div>

Maybe I am making it too difficult in my head.  
Basically the onPDMdata() function copies the recorded data to the sample buffer. Because of the few seconds that I have to record, I could maybe even stop recording after a timeout and handle the recording then.  
Like:

```arduino
 PDM.onReceive(onPDMdata); 
 if (!PDM.begin(1, sampleRate)) { // Initialize PDM with 1 channel (mono) and the specified sample rate
    Serial.println("Failed to start PDM!");
    while (1);
  } else {
    Serial.println("PDM started successfully.");
  }
  delay(1000);
  PDM.end;
  processAudio();

```

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<div class="post-metadata">

**Author:** ![anon94801460](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@anon94801460](https://forum.arduino.cc/u/anon94801460)\
**Post date:** [July 15, 2024, 2:54pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/28 "2024-07-15T14:54:00Z")

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Please answer the question.

I posted a complete, working example showing how to collect and store a short bit of PDM audio. Did you even look at it, or make any effort to understand the code?

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<div class="post-metadata">

**Author:** ![murosic](https://avatars.discourse-cdn.com/v4/letter/m/848f3c/32.png) [@murosic](https://forum.arduino.cc/u/murosic)\
**Post date:** [July 15, 2024, 2:55pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/29 "2024-07-15T14:55:49Z")

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> [@anon94801460](#):
>
> > [@murosic](#):
> >
> > ```arduino
> > for (int i = 0; i < audioSamplesRead; i++) {
> > cpBuffer[2 * i] = (sampleBuffer[i] >> 8) & 0xFF;
> > cpBuffer[2 * i + 1] = sampleBuffer[i] & 0xFF;
> > }
> > 
> > ```
> 
> What is the above supposed to be doing, and why?

I found that [on the forum](https://forum.arduino.cc/t/nano-33-ble-sense-recording-to-wav-file/1002497) ; it is to convert 16 bit audio to 8 bit to store it on a SD.  
My problem for now is before that conversion already, that strange data is recorded.

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<div class="post-metadata">

**Author:** ![anon94801460](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@anon94801460](https://forum.arduino.cc/u/anon94801460)\
**Post date:** [July 15, 2024, 2:59pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/30 "2024-07-15T14:59:02Z")

</div>

In that forum post, the OP is asking why the code doesn't work as expected, and did not get an answer. So it was not a good example to follow.

The code you copied swaps bytes (for some unknown reason), and makes nonsense of the data.

---

<div class="post-metadata">

**Author:** ![murosic](https://avatars.discourse-cdn.com/v4/letter/m/848f3c/32.png) [@murosic](https://forum.arduino.cc/u/murosic)\
**Post date:** [July 15, 2024, 3:12pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/31 "2024-07-15T15:12:16Z")

</div>

> [@anon94801460](#):
>
> Please answer the question.
> 
> I posted a complete, working example showing how to collect and store a short bit of PDM audio. Did you even look at it, or make any effort to understand the code?

What question do you mean?  
Yes I did the effort. While it is nice that the shared example works, I try to make a more lean program than this; this solution depends on a heavy library with lots of dependencies where most code will not be used. Besides, I am first focussing on recording data, and planned to dive into storing it on SD later. I try different paths and improve step by step, and along the road learn from it.

---

<div class="post-metadata">

**Author:** ![rsmls](https://avatars.discourse-cdn.com/v4/letter/r/5daacb/32.png) [@rsmls](https://forum.arduino.cc/u/rsmls)\
**Post date:** [July 15, 2024, 3:19pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/32 "2024-07-15T15:19:55Z")

</div>

> [@murosic](#):
>
> The basic principle is that a state is changed based on the input

No, the basic principle is that the system has a pre-determined number of well-defined states, and that the logic for switching between these states is equally well-defined and in line with the system requirement. This doesn't mean that state changes occur necessarily based on a momentary input. They can also be triggered by a certain amount of time passing, a sequence of inputs, data being fed to the controller through some kind of interface etc.

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<div class="post-metadata">

**Author:** ![anon94801460](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@anon94801460](https://forum.arduino.cc/u/anon94801460)\
**Post date:** [July 15, 2024, 3:24pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/33 "2024-07-15T15:24:02Z")

</div>

> [@murosic](#):
>
> What question do you mean?

The one you attempted to answer in post #29 above, but failed.

Good luck with your project!

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<div class="post-metadata">

**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\
**Post date:** [January 11, 2025, 3:24pm UTC](https://forum.arduino.cc/t/how-to-refer-to-the-built-in-microphone/1277606/34 "2025-01-11T15:24:36Z")

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