[pulseaudio-discuss] Bluetooth A2DP aptX codec quality

[Luiz Augusto von Dentz]

Hi Valdik

On Fri, Sep 14, 2018 at 3:39 PM, ValdikSS <iam at valdikss.org.ru> wrote:
> On 12/09/2018 19:03, Luiz Augusto von Dentz wrote:
>>> 2) Should we rather look at increasing quality of SBC codec in
>>> pulseaudio? And if yes, how should be quality of SBC configured? Via
>>> profiles? Or to invent some new protocol options? Can we increase
>>> default SBC bitpool allocation?
>>
>> I recall setting it to 64 before, but perhaps we are using 53 given
>> that most headset set that as maximum influenced by the spec suggested
>> values, I wouldn't go above 512kbit/s since then leave very little
>> room for any other traffic.
>
> I propose to use 76 bitpool as a default maximum (454.8 kbps for Joint Stereo, 44.1 kHz, 8 subbands, 16 blocks). This bitpool is optimal for both EDR 2 mbit/s and EDR 3 mbit/s modes, since it packs audio frames with least wasted bytes possible.
> EDR 2 mbit/s: up to 4 audio frames, 11.7 ms, 2 wasted bytes
> EDR 3 mbit/s: up to 6 audio frames, 17.5 ms, 14 wasted bytes.

That is a bit too hight I would say, and not sure if there would be
any headset to make use of it.

> Note that Pulseaudio/bluez (not sure which) does not manage L2CAP MTU correctly. For EDR 2 mbit/s, MTU should be set to 679 (ignoring higher values upon negotiation), and EDR 3 mbit/s should use 1021 (right now something like 800 is used).

We could do that if we know the packet type used by the link but that
is not how it is currently done in BlueZ, we always use L2CAP default
in case the socket don't set it:

https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/tree/include/net/bluetooth/l2cap.h#n34

Where did you get these values from btw?

>>
>>> 3) If aptX is decided as useless, what about aptX HD codec? aptX HD
>>> codec is supported by less products (currently I do not own any), but
>>> this one may provide better quality as SBC according to that research.
>>
>> That is probably useful as something that provides a quality
>> improvement compared to SBC.
>>
>>> PS: That aptX research is the first and the only one about which I know.
>>> All other information about quality or other details which I found on
>>> internet are just marking informations.
>>
>> I had some suspicion before given that no manufacturer provided any
>> evidence aptX would beat SBC at the same bitrate, it is probably
>> better just because we are stuck at 53 bitpool with SBC while aptX can
>> probably have much higher bitrate. Anyway thanks to the researcher for
>> putting the time to evaluate the codecs we now have a good reference
>> for the quality each codec provides.
>>
>>
>>> --
>>> Pali Rohár
>>> pali.rohar at gmail.com
>>> _______________________________________________
>>> pulseaudio-discuss mailing list
>>> pulseaudio-discuss at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
>>
>>
>>
>
>



-- 
Luiz Augusto von Dentz