I'm working on ADAU1772 evo.board with a PDM MEMS microphone.

Microphone's clock is 3.072MHz. DSP Master Clock is 12.288MHz. DSP sampling rate is at 192kHz and all DSP modules work with 192kHz.

1st Problem:

It was a clear sound from the microphone, but when I add ~35dB of gain, I started to hear a strange cracks from the headphone. It was like a clock sound.

I measure the output signal with an oscilloscope , there was a huge 20dBV of noise at around 60kHz-150kHz. That noise was not related with gain. Gain just make the sound hearable from the headphones.

When I changed my sample rate to 96kHz, that noise has disappeared.

But i need my block work on 192kHz.

2nd attempt:

I've change my main clock divider to 2. And my clockout to MCLK/2 (6144Mhz). But it should actually be 3072Mhz because it's now MCLK/2/2...

As it can be seen on the picture, My main blocks are operating in MCLK/2 (6144MHz). But still my sample rate is selected as 192kHz.

This helped with the noise.

enter image description here

Main Problem

Now my blocks frequencies are shifted. When I make a change in 100Hz, it affects 50Hz. The usual sample rate problem. But I don't know why is that related with the clock settings?



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