I had this thought just now at the gym. I noticed multiple people, myself included, using wireless earbuds during our workouts – specifically AirPods.
My question is, if multiple people are using AirPods that work on the same frequency/signal, how come our music doesn’t all interfere with each other? How do each of our phones/AirPods differentiate from the others a few feet away from me?
In: Engineering
Because each person’s earbuds are paired to their phone. You are thinking of it more like a radio signal, where any device is able to intercept the signal, but it doesnt work like that for a paired device. Each device has a signature that is recognized by the other device it is paired to, and signals can only go back and forth between the devices when they both agree to share their signatures through pairing
They’re not all actually using the same frequency. They work within a spread of frequencies, and your phone and the headsets work together to find a clear space within that spread and avoid bumping into other people’s phones and headsets.
That’s an extreme oversimplification but that’s the general gist of it.
You turn on your AirPods.
AirPods: “hey, phone, are you there? It’s AirPods 123. Remember me?”
Phone: “yup! Let’s connect. Frequency 8.56 seems pretty empty today, let’s use that one.”
AirPods: “ok! Tuning to frequency 8.56”
Phone: “and our secret code today is XYZ456, ill put that in front of all the data packets I send you”
AirPods: “got it! I’ll ignore any data packets that don’t start with XYZ456”
Phone: “here comes the music!”
It’s like the mailman bringing your mail everyday. He’s got your mail and your neighbors mail all in the same bag. But he decides who gets mail by the address on the letters. Bluetooth works kind of like this. Each set of earbuds have their own address. So they only received the letter that is addressed to them.
If you were on a conference call or just like a crowded restaurant or something, there can be several conversations going at once. It doesn’t all have to be 1 conversation. Even if there’s some other noise going on.
Each person just speaks with a different tone of voice, and you listen to the voice that matters to you while ignoring the rest.
That’s basically what the Bluetooth devices are doing. Just listening to the frequency that matters to them.
Not a scientist, but won’t there be interference? If you have enough radio traffic in the same band, similar to wifi etc.
Your airbuds won’t play or process another’s signal, but they will receive and filter it out?
Potentially missing or delaying received information from your phone.
oh dang you’re right. I remember back in 2016-2018 I would get interference in the gym. Not severely but I remember them making that interference noise every now n then
Not been on the packed concourse at Euston station I see? 😂
The frequency band for consumer electronics is fairly large, and as we’ve made better antennas, we can distinguish signals in smaller and smaller segments of it. That means we can have many many devices operating near each other that are all on slightly different ranges in that large band.
Beyond that, the communication protocols do have systems in place to do random backoff and repeat when they detect interference. That’s why bluetooth audio has a latency to it — it needs a buffer for when that interference does happen.
Digital communications over radio frequencies might as well be magic compared to the beginning of radio back in the 1920s or so. CDMA (code division multiple access) technology which is the part of most protocols effectively just transmits a signal into a giant pile of noise from everything else. The other side of the transmission is decoded by just mathing the hell out of what that noise consists of. Multiple sites just broadcast over each other and filter out what isn’t theirs.
The frequencies that unlicensed devices operate in (433MHz, 900MHz, 2.4GHz, 5GHz and others) are cesspools of transmissions from everything and anything. Somehow we have used an alchemy of physics and math to make it work.
That’s just the transport layer for communications, once you get beyond that you enter encryption and other protocols for actually transmitting useful data.
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