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Why does FM sound better than AM?

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259 points zdw | 1 comments | 13 Oct 24 22:32 UTC | HN request time: 0.194s | source
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matrix2003 ◴[14 Oct 24 00:15 UTC] No.41832921[source]▶
Someone gave me an analogy some time ago that made a lot of sense.

If you shine a flashlight through a tree blowing in the wind and vary the brightness to convey information, the signal can get distorted pretty easily.

However, if you have a constant brightness source and vary the color, it’s a lot easier to figure out what the source is trying to convey.

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ra ◴[14 Oct 24 05:57 UTC] No.41834625[source]▶
That's not the real story. The RF environment is noisy, with naturally occuring static "sparks", but also with manmade RF noise.

This static and RF noise is AM. It's impossible to filter it out from an AM signal, and so the background noise gets amplified with the signal.

Encoding the signal in a modulated frequency (FM) means we don't need to amplify the detected AM signal and it's associated background noise.

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1. Sesse__ ◴[14 Oct 24 07:26 UTC] No.41835096[source]▶
It's not that simple, though. The only way you can detect frequency is by measuring the amplitude (and then differentiate; except of course in an analog circuit, you don't do that exactly, you have some mechanism that tries to track the carrier wave smoothly instead), so amplitude noise will necessarily also become frequency noise. But generally white AM noise will be pushed upwards in the spectrum after FM demodulation, away from the area where you care. (You can also add a hard limiter, which amplifies this effect; even more noise high up, even less noise further down.)