Must work at 2.4Ghz--even in the face of 200 WiFi access points and 3 times that number of devices.
Must stay in sync to within a millisecond ... even though there is a large bag of RF absorbing water in between them.
Should work on a battery smaller than a thumbnail.
Should process audio but not generate enough heat that you notice it in your ear.
I can go on. The engineering requirements are quite severe.
... for something that we can do with a 10 cent wire, ironically.
At low range and less than 1/100 the speed of wifi.
> Must stay in sync to within a millisecond
If you have a working data connection at all, that level of sync is trivial. It only takes a few bits to align things, and they use pretty big buffers.
> even though there is a large bag of RF absorbing water in between them
That's hard.
> Should work on a battery smaller than a thumbnail.
That part is quite hard. But also it doesn't apply to over-ear headphones.
> Should process audio but not generate enough heat that you notice it in your ear.
I'm skeptical of that part being hard. How many milliwatts do those codecs take? Also once you add the battery constraints then the heat levels solve themselves.
Previously there hasn't really been much official support and implementations are messy and differ across platforms.
Source: have worked with various BLE stacks. Getting this stuff working well is difficult. I have much respect for companies that actually get it to work reliably.
Funnily enough, I try to avoid Bluetooth as much as possible and everything is wired on my setups.
Requirements aren't crazy. It just needs to support uncompressed 96/24, full duplex.