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.
In: 85
Radio frequencies are super high, way beyond what you can hear. That’s why you need a “radio” to convert those high frequency changes into sound.
The audio frequencies get added to the base frequency of the radio wave in such a way that the distance between a low and high frequency remains the same. For example, if the chosen radio frequency is 1 MHz, you encode an 8 kHz audio signal as 1,008,000 Hz. The receiver is able to shift the spectrum down in a couple of steps. An audio channel has a limited space allocated for it, and the sound might appear muffled as the highest frequencies get cut off.
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.
Radio is all digital now, even from your car’s stereo. the audio you hear is transmitted as data.
The huge benefits of transmitting data instead of sound is that you can compress it, so you can use less radio power to transmit, and add correction algorithms, so that even if the signal is weak and losses occur, the receiver can “regenerate” what was emitted.
While there are many emitters everywhere now, the signal power used has decreased a ton. There is way less RF power around people and homes now than 40 to 70 years ago.
Jason_Peterson here describes how it was encoded before FM was used, on the AM band.
Edit: for all the downvoters around, I am talking about DAB.
The songs aren’t tuned to the radio stations frequency. Same with old antenna TVs people’s voices don’t get higher or lower as you changed the channel.
It kind of does. All audio sent over FM is modulated to fit within the data band it can handle.
>The full audio spectrum ranges form 20 to 20,000 Hz, but FM radio limits the upper modulating frequency to 15 kHz (cf. AM radio which limits the upper frequency to 5 kHz). Although, some of the signal may be lost above 15 kHz, most people can’t hear it anyway, so there is little loss of fidelity.
From [here](https://man.fas.org/dod-101/navy/docs/es310/FM.htm).
But it’s not the radio waves that affect the sound, it’s their ability to carry information that affects it.
Sound waves change the air. Radio frequencies change the ElectroMagnetic spectrum. Two totally different media.
TL;DR I could send you a Morse code message with a green laser pointer, red laser pointer, or a flashlight. The type of light doesn’t matter too much for what we’re doing with it.
I just went and opened my free gift so I could gift it to you.
I’m currently an engineering student majoring in electronics and communication and I would have loved to you have in my communication class.
Wonderful answer.
Are you asking: Despite having multiple radio waves (e.g. from different frequencies / radio stations) occupying the same space, how are the sounds they encode not mixed together when we finally hear them?
Terrestrial radio stations have a Carrier frequency. For example, 88.3 MHz. Another station within a certain range is required to operate at a different frequency. This is because if two radio signal sources with the same frequency operate in a certain range, depending on their power output, they will indeed cause interference with each other.
Each station is assigned a “channel” which has a bandwidth of around 200kHz.
The size of the bandwidth determines how much raw information you can transmit on that channel without interfering with other channels.
In simplistic terms, music can occupy a range of 20Hz to 20kHz. To encode this as an FM signal, we need to be able to modulate (change the frequency) of the carrier signal by around 20kHz. The rest of the 200kHz bandwidth is used for Stereo (left+right) signal, other information and spacing to avoid overlapping with other stations.
As to how radios lock on to a frequency that changes, you can look into superheterodynes and phase-locked-loops.
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