A cheap builtin audio chip is likely to have some sort of low pass filter in its amp to avoid smoking itself though.

The author's solution to this problem is to use a tuneable RF preamplifier which also acts as a low pass filter when tuning the low end of the 88-108 MHz band where most of the exotic channels lie.

A damping circuit is a type of low pass filter that reduces the electrometer's ac response so the low DC current can be measured accurately.