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 using the PMODI2S2 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}\$

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

Pictures:

Input signal(yellow) from wave gen and output signal(green) after the Biquad filter

Input signal(yellow) from wave gen and output signal(green) passthrough with the peripheral no digital processing