I bought STM32F4DISCOVERY board and I developed a software that records .wav file using MP45DT02 MEMS microphone on this board. .wav files that I record are really good (almost no noise).

I designed a board based on the schematics of this evaluation board. When I used the same software, I have high noise at the background. I also can't record my voice unless I shout or scream. You can listen the record by this [link](https://www.dropbox.com/s/x5zaerwpj925mwy/first_message.wav?dl=0).

I have 3.3 volts on the board and the capacitors are appropriate in terms of value and closeness to the microphone.

I have two boards and I have the same problem on both boards so it seems to me that the problem is systematic.

Could it be a problem of soldering or PCB cleaning after production of the board? Could it be a problem of noisy power supply? What could be the reason?

Edit: Below is the spectrum analysis of the two records. (Green: Eval board | Blue: My board)

![...](https://i.stack.imgur.com/KGPHE.png)

Edit 2: Below is the channel meter of the two records. (Top: Eval board | Bottom: My board)

![enter image description here](https://i.stack.imgur.com/PBjXx.png)