How can there be different fequencies (it’s a difference in wave-lengths right?) but the tone of the music doesn’t seem altered by it.
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You don’t really hear the radio waves (which are a type of light!), you hear the sound they encode. The encoding systems don’t pay attention to the base frequency involved.
Imagine sitting in a room and watching a roll of paper scroll by with a wavy line on it. Your job is to sing along – when the waves get bigger, you sing higher. When it flattens, you sing lower.
This is basically how ‘AM’, or ‘Amplitude Modulation’ radio works. The frequency of the line doesn’t matter, just how tall the waves are.
FM radio is based on frequency, but it’s *relative* frequency that matters. So you’d sing higher when the waves get closer together, and lower when they’re farther apart. Again the exact base rate doesn’t matter.
Some interesting problems arise with both of these methods – for example, AM radio tends to crap out a bit when there’s stuff in the way that muffles it (like going under a big bridge or a tunnel or something). This is basically because your radio can’t tell if the line is flattening because it’s supposed to play lower music, or because there’s a big chunk of cement in the way!
FM is more robust as you just need to get enough signal to tell how far apart the waves are coming. However, you need more bandwidth for this kind of signal – the highest pitches you want to send on a radio channel can’t interfere with the lowest pitches from the next channel up. So there’s less airspace for FM radio.
Modern radio uses more complex encoding systems than what I’ve written here, but the basic principles are still the same.
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