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.
