ADMP421 bias in output signal.

Are you using the digital or analog outputs from the ADAU1761 in your system? If you're using the analog outputs, then a dc offset shouldn't be much of an issue because the analog outputs will most likely be ac-coupled (unless you're using the virtual ground with the headphone outputs). If you're using the digital outputs, are you setting the ADAU1761 to output a 16-bit word or are you truncating the data in a subsequent processor? If you're reducing the bit depth in another processor, you may want to consider dithering the data, rather than just truncating.

You could certainly implement a high pass filter in your SigmaStudio project to filter out these low frequencies. You wouldn't necessarily have to set the filter corner as low as the ADAU1761's built-in filter, since the microphone's low frequency corner is at 100 Hz. I'm not sure why the time constant of that high pass filter seems to be so long. If you have additional questions about that, you may want to ask those in the SigmaDSP section of EngineerZone: https://ez.analog.com/community/dsp/sigmadsp

Are you using the digital or analog outputs from the ADAU1761 in your system? If you're using the analog outputs, then a dc offset shouldn't be much of an issue because the analog outputs will most likely be ac-coupled (unless you're using the virtual ground with the headphone outputs). If you're using the digital outputs, are you setting the ADAU1761 to output a 16-bit word or are you truncating the data in a subsequent processor? If you're reducing the bit depth in another processor, you may want to consider dithering the data, rather than just truncating.

You could certainly implement a high pass filter in your SigmaStudio project to filter out these low frequencies. You wouldn't necessarily have to set the filter corner as low as the ADAU1761's built-in filter, since the microphone's low frequency corner is at 100 Hz. I'm not sure why the time constant of that high pass filter seems to be so long. If you have additional questions about that, you may want to ask those in the SigmaDSP section of EngineerZone: https://ez.analog.com/community/dsp/sigmadsp