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How to use the PDM_FIlter function

LCher.1
Associate

Hi,

I created a small board with STM32F446MEY6TR and SPK0415HM4H-B MEMS microphone. I can read the data from the mic via I2S interface in a chinks of 100*16 samples. Now I want to filter the data with the PDM_FIlter function, but I'm not sure how to pass the arguments, as UM2372 is not very specific about this. Here is my main function:

int main(void)
{
  /* USER CODE BEGIN 1 */
 
  /* USER CODE END 1 */
 
  /* MCU Configuration--------------------------------------------------------*/
 
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
 
  /* USER CODE BEGIN Init */
 
  /* USER CODE END Init */
 
  /* Configure the system clock */
  SystemClock_Config();
 
  /* USER CODE BEGIN SysInit */
 
  /* USER CODE END SysInit */
 
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_CRC_Init();
  MX_PDM2PCM_Init();
  MX_I2S2_Init();
  /* USER CODE BEGIN 2 */
 
  uint16_t pdm_data[100];
  int16_t pcm_data[16];
 
  /* USER CODE END 2 */
 
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
	  // read the i2s data
	  HAL_StatusTypeDef result = HAL_I2S_Receive(&hi2s2, &pdm_data[0], 100, 100);
 
	  uint32_t error_code = PDM_Filter(pdm_data, pcm_data, &PDM1_filter_handler);
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */
}

The PDM_FIlter function returns values from -8 to 8, which is too less.

Thank you!

1 REPLY 1
Eleon BORLINI
ST Employee

Hi @LCher.1​ ,

even if you are using a non-ST microphone (it's from ), the PDM_filter function should work in the same way.

Can you please first check this other community thread, if it might be related to your issue?

-Eleon