PDM Sample Buffer

[eng]

Hi,

I found your PDM Working Example. However I wonder what to make of the data I get.

What is the CONFIG_PDM_BUFFER_SIZE_SAMPLES for? Do I get 16Bit Bit-Schemes from which I must assemble my PCM Data or are there lets say 64 PCM Samples in the buffer.

Is there any Chance to configure the Decimation to different values?

Regards Daniel

[Sigurd]

Hi,

The CONFIG_PDM_BUFFER_SIZE_SAMPLES is used to set the number of samples to allocate memory for in EasyDMA mode.

The PDM bitstream is converted into 16-bit PCM samples by the digital filter, and is then filtered and down-sampled to reach the appropriate sample rate.

You can configure the Decimation Filter Gain by adjusting the GAINL and GAINR registers.

Snippet from the drv_audio_init() function in Thingy:52 SDK:

ret_code_t drv_audio_init(drv_audio_buffer_handler_t buffer_handler)
{
nrf_drv_pdm_config_t pdm_cfg = NRF_DRV_PDM_DEFAULT_CONFIG(CONFIG_IO_PDM_CLK,
                                                          CONFIG_IO_PDM_DATA,
                                                          m_pdm_buff[0],
                                                          m_pdm_buff[1],
                                                          CONFIG_PDM_BUFFER_SIZE_SAMPLES);
.
.
.
pdm_cfg.gain_l      = CONFIG_PDM_GAIN;
pdm_cfg.gain_r      = CONFIG_PDM_GAIN;

.
. 
.


return nrf_drv_pdm_init(&pdm_cfg, drv_audio_pdm_event_handler);
}

[eng]

Thank you! So do I understand correctly, that, when I want to get the already converted PCM Data, I just need to count the address upwards, dereferencing the *p_buffer pointer in *static void m_audio_buffer_handler(int16_t p_buffer, uint16_t samples) while doing so?

[Sigurd]

Yes, that is correct

[sara]

Hi , Sigurd, how to get the pdm data ? I am not able to get the data when configured with EasyDMA.