[pulseaudio-discuss] SBC XQ for PA 13.0

[Andrey Semashev]

On 2019-12-09 14:39, Pali Rohár wrote:
> On Monday 09 December 2019 14:32:52 Andrey Semashev wrote:
>> I have another piece of feedback to provide. Sometimes I experience audio
>> dropouts. Sometimes in both left and right headphones, sometimes just one.
>> In particular, I noticed this happen when I have a Bluetooth-connected
>> DualShock 4 gamepad connected and playing games, but it also happens without
>> it, although less often.
>>
>> I assume this is caused by Bluetooth bandwidth limitation. Note that EOZ Air
>> are "truly wireless" (i.e. the two headphones connect wirelessly), and I
>> have multiple WiFi networks available (one access point in the same room as
>> the Bluetooth transmitter, a few others behind walls). I expect 2.4 GHz
>> radio to be rather crowded. The gamepad and the headphones are in the same
>> room as the Bluetooth transmitter, in clear direct visibility, so it can't
>> get better than that.
> 
> Yes, 2.4 GHz is shared by both Bluetooth and WiFi, so it may be a
> problem.
> 
>> I can see Pali's patches offer reduce_encoder_bitrate API that is supposed
>> to mitigate this problem, but both SBC XQ profiles don't allow bitrate
>> reduction.
> 
> Yes, SBC XQ is there the highest available quality profile of SBC.
> 
>> I think, SBC XQ desperately needs to support bitrate reduction,
> 
> No, this is main reason for usage of SBC XQ it is high quality codec.
> SBC XQ needs high bitrate by its definition.
> 
>> as the codec with the highest bitrate out of all. Users might actually have
>> reduced experience due to audio dropouts compared to the previously
>> supported SBC HQ.
> 
> If you cannot use high bitrate codecs, then do not use high bitrate
> codecs. There are other profiles of SBC which lower bitpool value and
> therefore lower bitrate. E.g. SBC MQ or SBC LQ (medium and low quality).
> 
> Or you can use SBC in automatic mode where bitrate is automatically
> decreased.

As a user, I don't know whether I can use SBC XQ. I don't know whether 
its bitrate will fit in my radio conditions. If my device happens to 
support SBC XQ, that is the codec that will get picked upon connection. 
Please, correct me if I'm wrong, but I don't see a way to influence that.

SBC XQ is high quality and high bitrate, true, but PA should adapt to 
the actual use conditions. More so if it actually has the means to do 
so. If PA detects that SBC XQ does not fit in BT bandwidth, it should 
gradually drop quality.