Thought this would deserve a separate post on its own. 

What's going on is that I finally got my low pass digital filter working on the [STM32H753ZI][1] using the [PMODI2S2][2] peripheral and I noticed the output signal is extremely low ~340mVpp this is after the biquad filtering. If I take out the low pass filtering the output signal then raises to around ~600mVpp.

What's causing this phenomenon? The digital filter bode plot says the gain from very low frequencies up to the cut off is 0dB so I dont understand whats going on. The only thing I can think of is the biquad filter is causing an attenuation perhaps? 

Analog Filter: \$ LPF_{Analog}=\frac{3.94e07}{s^2+8889s+3.94e07}\$

![enter image description here][3]][3]

Digital Filter: \$ LPF_{Digital}=\frac{0.00102z^2 +0.002041z+0.00102}{z^2-1.908z+0.9116}\$, using tustin

[![enter image description here][4]][4]


Pictures:

Input signal(yellow) from wave gen and output signal(green) after the Biquad filter
[![enter image description here][5]][5]

Input signal(yellow) from wave gen and output signal(green) passthrough with the peripheral no digital processing
[![enter image description here][6]][6]


  [1]: https://www.google.com/search?rlz=1C1CHBD_enCA841CA841&sxsrf=ALeKk0181J_yj10LYaGo5FVNDbOKMr78Qg%3A1602789035623&ei=q56IX_2-JZH5tAbGzr2YAw&q=stm32H753zi&oq=stm32H753zi&gs_lcp=CgZwc3ktYWIQAzIECCMQJzIECCMQJzIECCMQJzICCAAyBAgAEB4yBAgAEB4yBAgAEB46BAgAEEdQvxhYvxhg9xxoAHACeACAAWCIAWCSAQExmAEAoAEBqgEHZ3dzLXdpesgBCMABAQ&sclient=psy-ab&ved=0ahUKEwi9wPi4prfsAhWRPM0KHUZnDzMQ4dUDCA0&uact=5
  [2]: https://reference.digilentinc.com/reference/pmod/pmodi2s2/reference-manual
  [3]: https://i.sstatic.net/0JCTN.png
  [4]: https://i.sstatic.net/pK42P.png
  [5]: https://i.sstatic.net/l7nsc.png
  [6]: https://i.sstatic.net/lt0lW.png