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