MPX Filter - What does it actually filter?

Investigating the oft-misunderstood button or switch found on many high-end cassette decks: the MPX filter. What does it actually do? How come it usually seems to have no audible effect? Let's find out. Another mystery is the Beat Cut switch found on many boomboxes and integrated stereo systems: https://www.youtube.com/watch?v=gm0dT-vi0XU Time flow: 0:00 Introduction 2:32 RTFM 3:55 Pilot tone 5:50 FM transmitter test 9:24 What it doesn't do 10:10 Effect on audio quality? 12:01 Not always necessary 13:29 Conclusion #cassette #audiophile #RetroTech