jallison
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Apple is trying to reinvent group audio chat with no cell or WiFi needed
AppleZulu said:WiFi has greater range and capability of transmitting through walls and other obstacles, but sure, go with Bluetooth if that doesn’t matter to you.
There are also two levels of 'long range' in Bluetooth 5 - Coded Phy S2 and S8. They increase the range between handsets to ~100m. Apple doesn't expose these to developers for use in iOS - but all iPhones since iPhone X support it (they were briefly available in an iOS 13 beta I think). Android does have APIs for using these long range modes. From first hand experiments - Bluetooth LE Coded Phy S8 travels further than a WiFi hotspot from the same phone.
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Apple is trying to reinvent group audio chat with no cell or WiFi needed
Now, 125 kbps is sufficient for a voice call (voice land lines digitize to 56 kbps), but would that be enough for modern users who are used to the quality of a VoLTE call?
Another thing to bear in mind is that the codecs and bitrates chosen for Bluetooth headsets are mainly chosen to optimise battery life (and component cost) - so balancing the power needed for the codec complexity in the MCU to compress the audio vs the power needed to transmit the data. If you've already got a powerful CPU and a comparatively huge battery - and aren't trying to make the whole thing fit in someone's ear - you can make some different codec choices and really get the bitrate down on a phone.
The Opus codec ( https://opus-codec.org ) at 64kbps (less than half Coded Phy S8s 125kbps) is pretty much transparent (to me) 48kHz Stereo - which would be fine for a one-one call. This codec is used by Google's Pixel Buds Pro for its spatial audio implementation.
For group calls - and bearing in mind modern phones do not lack in compute - if you can tolerate a drop to wide-band (which most 'Classic' Bluetooth headphones would force anyway) Google has made their Lyra V2 codec open (and MIT licenced) - which goes down to just 3.2kbps - which would allow 40 channels on Coded Phy S8. It's worth checking the samples at ( https://opensource.googleblog.com/2022/09/lyra-v2-a-better-faster-and-more-versatile-speech-codec.html ).
Meta also has MLow - which at 6kbps also does wide-band, but at a lower complexity than Opus. Meta seem to be keeping this proprietary though ( https://engineering.fb.com/2024/06/13/web/mlow-metas-low-bitrate-audio-codec/ )
Another low bitrate codec is LMCodec (https://arxiv.org/pdf/2303.12984). This goes down to 0.5kbps, and still sounds very acceptable (there was a project page with very impressive samples at ( https://mjenrungrot.github.io/chrome-media-audio-papers/publications/lmcodec/ ) - but it's doing odd things today). Voice codecs below 0.7kbps come under export controls in the UK ( https://assets.publishing.service.gov.uk/media/660d281067958c001f365abe/uk-strategic-export-control-list.pdf ), and I've heard 3.2kbps for some other countries, so I'm not expecting to see that appear in the wild. -
Apple is trying to reinvent group audio chat with no cell or WiFi needed
I've spent a bit of time working on an app which does this using Bluetooth LE (so I'm kind of hoping that would count as prior art re. the patent application...). It's still a little rough - but works on Android and iOS and is available in the respective app stores 'Murmur : Bluetooth Group Calls'. I've been using it for cycling with my family.
Of course Apple can use Coded Phy for increased range, and send BLE advertisements when the screen is off - so their implementation will likely be free of the artificial restrictions on iOS.