jallison

shamino said:

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?

125kbps is indeed sufficient for voice - many voices in fact. Addressing quality of a VoLTE call first - although the spec for Enhanced Voice Services goes up to 48kHz (FullBand) - Most 'Classic' Bluetooth headphones only support 16khz for voice calls (WideBand).  The mics in Airpods Pro 2 top out at 24kHz for voice calls (though the earbuds themselves do have another 'Spatial Audio' mode which plays 48khz stereo - and is currently used by facetime - I don't know if it's 2-way). Whilst AptX Adaptive Voice apparently supports 32khz (SuperWideBand) voice calls - I've not yet managed to find a phone that supports it. LE Audio is starting to appear now - the spec for this is mandatory 32kHz for voice calls. Anyhow - my point is that 32kHz mono is pretty much the most people are going to be able to do anything with (and for many, 16kHz - which really, for voices, does sound completely fine). 

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/ )

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. 

This isn't true - Both use 2.4GHz (and 5GHz does not go through walls anywhere near as well). Your WiFi router likely has a huge antennae on it which isn't really a fair fight - try using the WiFi hotspot from a phone for a fair comparison.

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.