PDM Mic data to Speaker not Working

[nikul]

Hi,

I am working on a project involving a PDM microphone and an I2S speaker.

Hardware:

• PDM microphone: MP34DT01-M

• MCU: nRF54L15

• Speaker amplifier: I2S input

• PDM microphone is connected to the nRF54L15 PDM interface.

• Speaker amplifier is connected to the nRF54L15 I2S TX interface.

I am able to successfully read audio data from the PDM microphone using the Zephyr dmic_read() API. The data returned by dmic_read() is in PCM format.

However, I am facing an issue when trying to play this PCM data through the I2S speaker.

What I have tested

1. I configured the PDM microphone and can successfully capture data using dmic_read().

2. I wrote the PCM data returned by dmic_read() to an external flash file.

3. I played the recorded RAW PCM file separately, but I hear only noise.

4. I also tried sending the PCM data directly from the PDM microphone to the I2S TX interface.

5. In both cases, the speaker produces only noise instead of the expected microphone audio.

The I2S interface is configured with the required:

• BCLK / SCK

• LRCLK / FCLK

• SDOUT / DATA

What I need help with

Could you please review my source code and help identify the problem?

In particular, I would like to verify:

• Whether the PCM data produced by dmic_read() is actually valid audio.

• Whether the PDM microphone configuration is correct.

• Whether the PCM sample format, sample rate, bit depth, and channel configuration are correct.

• Whether the I2S TX configuration matches the PCM data format.

• Whether there is an issue with signed/unsigned PCM data, sample width, channel format, or byte ordering.

• Whether the I2S clock configuration is correct for the speaker amplifier.

• Whether the DMA/buffer configuration could be causing corrupted audio.

• Why the RAW PCM file contains noise even when played separately.

• Why the direct PDM-microphone-to-I2S path also produces only noise.

I have provided my PDM microphone driver, I2S speaker driver, device-tree overlay, prj.conf, and the captured RAW PCM file in attachment .8475.Mic_POC.zip

Please analyze the complete code and identify the exact issue, if possible, and provide the required code/configuration changes to get clean microphone audio through the speaker.

[Hung Bui]

Hi, 

You will need modify the sample to either save the dmic_read() data to flash and read it out or print it via UART. 
Attached is my code. It will record the first 5 seconds and print it out on UART. You will need to use a tool on UART to capture the data and put into a file. 
I use Real Term for that but you can make a some python code as well: 

UART baudrate is 1000000. 

A quick check is to look at the data, for example when it's quiet , you should see very low number (second byte close to 00 or 01 ) like this: 



When there is sound/talking you should see this: 

If you still see the issue, please try to test with other microphone, also show us how you connect the microphone to the chip. Make sure you have right voltage (if you use 1.8V on the VDD then the nRF54L should be supplied with 1.8V as well). 

5140.dmic.zip

[nikul]

Can you check Below Raw data captured from d_mic() API.
raw.txt

[Turbo J]

Use audacity.

Also check your pinout - on NRF54 the GPIO pins must be on the same power domain as the peripherial driving them.Would trigger my hourly rates if you wanted me to check that for you.