For testing I've connected a function generator to the audio codec analog line in (header J7) and I'm giving the output of the SPL to an oscilloscope to check the output for attenuation or gain. So far, I've created a Biquad lowpass and I've noticed attenuation on some occasions. Sometimes it works, sometimes it doesn't and I'm yet to figure out how to make the filter work properly.
Is there something that I'm missing? Please let me know if any additional details are required.