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259 points zdw | 3 comments | | HN request time: 0s | source
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matrix2003 ◴[] 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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tejohnso ◴[] No.41833256[source]
This seems great at first, but more so as an explanation of how AM and FM differ; one being by amplitude (brightness), and the other by frequency (color).

What I don't see is how it explains why one would work better than the other.

If the tree is blowing in the wind, and a leaf obstructs the entire signal, it doesn't matter whether it's a change in brightness, or a change in color. Either way, that information is lost by the blocked leaf. And if the entire signal is not lost, perhaps many leaves may have blocked the signal but some signal managed to get through, it doesn't matter whether the signal change was a change in brightness, or a change in color. Either way you're going to notice the change. So I don't see how this clarifies why FM is better. What am I missing?

I see from the article that "noise tends to be a an unwanted amplitude modulation, not a frequency modulation." In other words, the tree is providing an unwanted change in brightness. It never provides an unwanted change in color.

I guess the tree is able to dim the signal so much that it appears to be a deliberate signal change? Couldn't this be dealt with if you know the details of the tree's dimming ability?

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1. JumpCrisscross ◴[] No.41834152[source]
Let's switch the analogy to sound. Amplitude is loudness. Frequency is pitch. You are trying to discern two sources of sound. One is a constant pitch but variable volume. The other can always blast at max volume with variable pitch.
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2. therein ◴[] No.41834184[source]
Also harder to discern and then quantify the loudness of a sound or brightness of a light as a human modem but we are better and more certain of the color. We have different names for the ranges and everything.
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3. JumpCrisscross ◴[] No.41834265[source]
> harder to discern and then quantify the loudness of a sound or brightness of a light as a human modem but we are better and more certain of the color

Fair enough, this might be a sensory artefact. In this case, however, nature had a point. Energy scales proportionally with frequency but exponentially with amplitude. Increasing amplitude delivers more bang than increasing frequency.