[tlug] bluetooth headset on Linux with HFP/HSP profile

[Christian Horn <chorn@example.com>]

Hi tlug,

I recently got a Bose QuietComfort 35 headset.

When connecting the headset via analog cable to Linux systems, I can
listen to audio output from the system - but not use the microphone 
of the headset.  The cable which came with the headset has 
3 connectors, so it is only transmitting stereo audio.


Using bluetooth, I can select 2 bluetooth profiles:

- A2DP: high quality audio, but does not transmit microphone
  signal to the system
- HFP/HSP: this provides microphone signal to the system, and also
  audio - but with a much lower quality than the A2DP profile.


I was wondering if I could improve the audio quality when using the 
headset for video conferencing.
The Hands-Free Profile (HFP) Version 1.6 adds optional support for 
wide band speech with the mSBC codec, a 16 kHz monaural configuration 
of the SBC codec which is also used (and mandated) by the A2DP 
profile.

So the bluetooth standard in version 1.6 should support better 
audio, I tried to find out if the involved software also supports 
it (and if yes, why it is not used), but got stuck.

- The bluez5 software stack on Linux seems to support HFP v1.6,
  according to [1].
- Just for the headset, I am unsure.  The headset specs state
  "bluetooth 4.1", but I am not aware of this resolving into 
  versions of the single profiles like HFP/HSP.  A question to 
  the Bose support did not help much either: I got a list of the 
  supported bluetooth profiles by name, but not the versions.  
  Also the combinations of software stacks they are testing as 
  part of QA "will not be disclosed" by them.  Not even saying 
  by which version of a protocol the own device claims to be 
  operating.. is very strange.

I have so far not tried to look at the communication between
bluez5 and the headset, seems to involve dbus and sockets.

Has anybody looked at similiar issues and/or good ideas for
finding out more?

Thanks,
Chris


[1] https://git.kernel.org/cgit/bluetooth/bluez.git/tree/doc/supported-features.txt