Question: what is modulation;demodulation;mismatch in telecommunication? 

Answer: A modem? (snickers)\n\nas simple as I can make this, when an audio or video signal is mixed with a radio frequency, the results is a modulated signal (like an AM radio station).  When you receive the signal, the radio waves are demodulated to seperate the audio and video from the higher radio freq.
This question from the Yahoo Q&A forum is categorized in the topic: Education & Reference