[MadDemon]

You have to down sample by a lot (easily 10-100x). That would essentially remove a lot of the information in the signal. If you low pass filter you essentially remove all the peaks and the signal looks much "quieter" than it actually is.

[chrisjj]

Agreed. In the worst case, the audio is simply a high-frequency tone - which the LPF removes, leaving the plot showing silence.

[wiz21c]

ahhh didn't see that one. Perfectly makes sense ! Thx for explaining.