←back to thread

Why does FM sound better than AM?

(www.johndcook.com)
259 points zdw | 1 comments | 13 Oct 24 22:32 UTC | HN request time: 0.224s | source
Show context
dmitrygr ◴[14 Oct 24 00:20 UTC] No.41832956[source]▶
This is 100% nonsense. Phase noise exists too, not just amplitude noise.

The answer is actually rather simple. AM stations are limited to 10KHz band width. FM gets 200KHz. More bandwidth allows representing a higher fidelity signal…

replies(5): >>41833000 #>>41833015 #>>41833074 #>>41833260 #>>41833414 #
crackalamoo ◴[14 Oct 24 00:41 UTC] No.41833074[source]▶
Yes, phase noise exists, but I would think that in practice amplitude noise is greater.

In physics, when a wave passes from one medium to another, its frequency is supposed to stay the same. Even if this isn't perfectly true in the real world, I would think amplitude is more likely to decrease due to obstacles, distance, and the medium absorbing some energy.

replies(2): >>41833219 #>>41834117 #
1. 317070 ◴[14 Oct 24 04:15 UTC] No.41834117[source]▶
But the two are the same thing. You took the fourier transform of white noise and find white noise, both real (amplitude noise) as complex (phase noise).

You can think of it like this: the noise is not about the phase changing, it is about your ability to tell what the phase is. The noisier the signal gets, the harder time you will have to tell what the amplitude is, as well as what the phase is.