[pulseaudio-discuss] Extra A2DP codecs support in bluetooth module

ValdikSS iam at valdikss.org.ru
Mon Jul 30 03:33:26 UTC 2018

On 22.07.2018 14:37, Pali Rohár wrote:

> Information which I have about FastStream: It is just SBC codec with
> following parameters: frequency rate 44.1 kHz or 48.0 kHz, Blocks 16,
> Sub-bands 8, Joint Stereo, Loudness and Bitpool = 29. So data rate = 212
> kbps, packet size = 72*3+4 = 220 = DM5 and that DSP decoders round 71
> bytes frames to 72 bytes. So I'm not sure how "low latency" it is.
> Normal SBC codec allows you to specify all those parameters. But
> FastStream has one additional feature: it supports backchannel for
> voice, so you do not have to switch between HFP/HSP and A2DP once you
> have incoming voice call. You can always use just A2DP with FastStream.
> Pulseaudio for SBC codec choose those parameters: Joint Stereo, Block
> 16, Sub-bands 8, Loudness. Frequency and bitpool depends on pulseaudio
> source. If bluetooth device does not support those parameters,
> pulseaudio lower values. So for me it looks like that FastStream matches
> default SBC pulseaudio configuration.
> Backchannel in FastStream for microphone voice again uses SBC codec with
> parameters: 16 KHz frequency rate, Blocks 16, Sub-bands 8, Loudness,
> Bitpool 32. So data rate = 72 kbps, packet size = 3*72 + 4 = 220 <= DM5.
> Which should be much better then CVSD codec at 8 kHz used in HFP/HSP.
> But is there really difference for voice data which comes from
> (probably poor) microphone integrated in headsets?
>> handful of Creative headsets that don't seem to support any other codecs. I
>> would put it between SBC and AAC. If someone prefers SBC over it, they know
>> enough about Bluetooth operation to qualify as a power user capable of using
>> the config file to disable FastStream.
> Based on above details I would say it must be similar (or same?) as SBC
> for streaming. But who knows how is receiver implemented? I would not be
> surprised if some bluetooth headset have degraded SBC A2DP codec just
> for marketing purposed to show that other vendor codec is "better".
> As I said, I need to play with FastStream and see what my headset would
> do with it. For me interesting part is that backchannel support to avoid
> all problems with switching between A2DP and HSP/HFP profiles (to
> activate HSP/HFP only in case I have incoming call and after hangup
> switch back to AD2P...).

It would be great if FastStream support could be implemented. I have a headset with CSR (now Qualcomm) chip which supports SBC, AptX, AAC and FastStream. The headset is rather unknown and not expensive (but surprisingly good), so I assume FastStream support is not that rare.
If high-quality duplex audio is possible with Bluetooth, that would be very handy for conferences.

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