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
While one part of the story is that all devices don’t work at same frequency, the bigger part is that these devices transmit sounds encoded as data. Sending a seconds worth of audio data can be done much, much faster than in a second, leaving time to send other audio data to other devices.
The data transmission isn’t continuous, it’s in packets of short audio recordings. As long as you get your next packet before the last one finishes playing, you’ll never notice.
How do you speak with other person in a crowded room? You raise your voice (increase transmission power), you exclude every tone of voice not belonging with your interlocutor (filters and channels). If you could you would change tone every time you speak with the other person and you would change even language so that nobody could understand you (frequency hopping and encryption).
I think u/02K30C1 has the best answer here… but I wanted to reply and say that your question is a bit misleading because they can interfere with each other.
As a commuter who goes between NYC and NJ, if you walk through the Oculus at One World Trade (where multiple subways converge in addition to shops and military personnel), you’ll experience this.
It’s a lot of stop and starting and odd pauses, so interference via Bluetooth does happen! It just takes a lot more people and devices.
Scrolled through this thread to find a name drop for [Hedy Lemarr](https://www.youtube.com/watch?v=Z0gu2QhV1dc)
It’s similar to how 1000s of cars can drive on the same highway at the same time.
Think of the highway as the total frequency bandwidth alloted to Bluetooth.
Think of the cars as your Bluetooth items
Think of the lanes as frequencies.
Cars, like your Bluetooth, only occupy so much space. I think BT range i’s intentionally limited to like 5 meters or something like that.
So even though you’re driving in the same lane as 100 other cars. So long as your car doesn’t occupy the same space at the same time as another car, you’re good to go.
Additionally, just like how some cars swap between lanes repeatedly, your Bluetooth does that too. They don’t stay on one frequency but randomly hop between them in intervals.
(You will get some overlap once in a blue moon, but it’s done so rapidly that a little bit of error here and there doesn’t really impact your experience)
this is a great 4 minute video explaining the basics of Bluetooth
Modern Bluetooth uses fast frequency hopping. Every few milliseconds the frequency is changed to one of the 79 possible channels. So 80 people in an 25ft radius using Bluetooth should have little to no interference.
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.
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.
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
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