system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do AM and FM radio signals sound so different?

A show I listen to on FM in the afternoons replays the next morning on AM, why does the AM station sound so much different?
gpt
Imagine writing out a message in your own handwriting, and later printing the same message with your printer. The letter will look wildly different. Your handwriting most likely is unclearer and more messy, but cheaper. Your printer makes everything perfectly clear and understandable, but printer ink is expensive.

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AM and FM are separate methods of encoding and broadcasting radio signals. M works by modulating the amplitude of the signal according to the information being sent, while the frequency remains constant. This differs from FM technology in which sound is encoded by varying the frequency of the wave and the amplitude is kept constant. 

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This difference in signal type is what causes the sounds to change. AM has poorer sound quality compared with FM, but is cheaper and includes lower bandwidth making it ideal for having many stations in a small broadcast range. FM has a sharper quality at the cost of higher bandwidth, but can be blocked by physical hindrances (mountains or your wall) making it much shorter range.