How to set the gain of the pdm module in nrf52832

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As I don't know much about audio,I have trouble with the gain of the pdm module in nrf52832.Now I have used MP45DT02 as the digital microphone,but I just can't understand the gain about the pdm module in the datasheet.I have tried to change the gain value,but it seem to have no effect on the audio.It also has too much noise.Could you give me some advice?

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According to the datasheet,I just connect the microphone with the PDM interface directly.I have transmited the PCM data to USB dongle,so PC can record the audio data with USB.However when I repalyed the audio,it sounded like a lot of noise. Yesterday I found that it lost data when I transmited the data with 2.4G.But I am not sure about that the lost data caused the noise.