←back to thread

Why does FM sound better than AM?

(www.johndcook.com)
259 points zdw | 2 comments | 13 Oct 24 22:32 UTC | HN request time: 0.435s | source
Show context
spease ◴[14 Oct 24 15:29 UTC] No.41838425[source]▶
I’m confused how this is even a question.

With AM, anything that causes a variation in the intensity of the signal will introduce noise.

With FM, anything that causes a variation in the timing of the signal will introduce noise.

Unless you’re traveling at relativistic speeds, operating a time dilation device, or colocated with a black hole, you usually aren’t going to see the rate that time flows at vary.

Thus if you can make the amplitude of your signal irrelevant past a certain threshold and embed all the information into the time domain, the only thing introducing interference should be other EM sources that happen to be on the same channel.

replies(5): >>41838630 #>>41838717 #>>41838999 #>>41839019 #>>41839404 #
_fizz_buzz_ ◴[14 Oct 24 16:20 UTC] No.41838999[source]▶
FM usually has higher fidelity than AM even if no noise is introduced.
replies(1): >>41839383 #
MBCook ◴[14 Oct 24 16:57 UTC] No.41839383[source]▶
Right. Isn’t FM just flat out higher bandwidth? So unless it’s wasting that somehow it’s just going to carry more information. And for audio, that means sounding better.
replies(1): >>41839788 #
1. cruffle_duffle ◴[14 Oct 24 17:35 UTC] No.41839788[source]▶
The use of FM doesn’t inherently imply higher bandwidth. For example, those consumer-grade FRS/GMRS radios you get from Costco use narrowband FM, which typically occupies about 12.5 kHz per channel. This is much narrower compared to the 200 kHz bandwidth used by FM broadcast radio.

FM is simply a method of modulating the carrier signal by varying its frequency. The actual bandwidth depends on factors like frequency deviation and modulation, so FM can range from narrow to wide bandwidth depending on the application.

replies(1): >>41843719 #
2. MBCook ◴[15 Oct 24 00:31 UTC] No.41843719[source]▶
Good point. I was referring to the public airwaves with the layman’s definition of “a radio”. But that was how it was chosen there.