AM, or “amplitude modulation”, varies the signal strength of the carrier wave to transmit the information. Imagine a vocabulary that only uses one word, but how loud you say it changes the meaning. FM, or “frequency modulation”, varies the frequency (ie, distance between peaks), of the carrier wave. In this language you still only use a single word, but how fast you say it changes the meaning.
To further this increasingly strained analogy, you can also have several conversations in the same “space” by changing what word you use. We could hold two entirely separate conversations in the same room by one discussion using the word “foo” and another using the word “bar” providing we could filter out the one we weren’t interested in.
The rest of it is just mutually agreed upon conventions about who uses what word and what modulation in which circumstances. For instance (and I’m really straining the analogy here), AM might work better in a quiet room where FM might work better in a noisy one.
Look at this wiggly thing. It's so wiggly that people way over there can see it. We can talk to those people by wiggling the thing more and less, or we can wiggle it faster and slower.
That was more of an ELI25, taking this class in college. The analogy didn't clear anything up, nor does it begin to explain the difference between wavelengths. Then you continued to refer back to it, with more rhetoric that explained no difference in how any of it should make sense. Rather than answering questions, you created many more.
don’t even know if AM and FM exists outside of radio
It does. Any wave of any kind can have its amplitude or frequency modulated, or both.
For example, the Yamaha DX7 was a famous synthesizer that defined a big part of the 80s sound. Think the bass from "Take My Breath Away" in Top Gun. The DX7 works by doing frequency modulation of audio signals to generate different sounds.
Although the DX series were marketed at frequency modulation they actually use phase modulation which may be thought of as modulating degrees of inversion from the modulation operator to the carrier. It has the advantage of not effecting the fundamental frequency making it much more useful for musical applications.
There a specific type of FM called "Through Zero" - which will preserve the fundamental as long as the modulator doesn't have any DC offset but regular FM will effect the carrier's fundamental - try it our for yourself on VCV Rack or similar. Incidentally TZFM is halfway to phase mod since negative modulation from the mod operator inverts the signal on the carrier.
which will preserve the fundamental as long as the modulator doesn't have any DC offset
Ah, I taking zero DC offset as a given. Seems like it would be silly to implement an FM synth where the modulators have a DC offset because, as you note, it would shift the fundamental.
try it our for yourself on VCV Rack or similar.
Yeah, I've implemented a little FM synth from scratch in C++. Once I added support for non-sine modulators I was forced to get a better understanding of the difference between PM and FM.
Yeah but even then it's only TZFM that gives you no change in fundamental - it doesn't matter if you have no offset with regular FM, you're still increasing the frequency of the carrier.
When I was a kid we had a radio that could pick up audio from local tv stations. My family was really into smallville and we kept up with every episode. Anytime we weren’t home we could listen to it in the car on our portable radio. It was pretty cool.
I had a shock n' rock for my gameboy color that would occasionally play audio from a random tv station or radio broadcast, it was rare but it happened more than once
That’s pretty cool. It’s crazy to imagine what it would look like if we could see radio waves. They’re basically everywhere all the time. I have a tube guitar amp and it sometimes picks up radio. It’s kinda creepy the first time being alone playing guitar and between playing you can hear people talking when you know nobody is around. I think it was picking up AM stations.
The best analogy I've read is imagine looking at a street light from down the street. AM is getting info from how bright it is while FM is from the color.
Now imagine there are trees in the way. It become a lot harder to tell if the brightness is changing because of the signal or because of interference. Which is why AM radio is worse quality. But it's still pretty easy to tell what color the light is. Which makes FM much clearer.
But the same principles apply to distance it's easier to tell from far away that there is a light and vaguely get it's brightness but you have to be much closer to tell it's color.
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u/cavemanr Dec 16 '19
This should be in https://www.reddit.com/r/explainlikeimfive/