[pulseaudio-discuss] Bluetooth A2DP aptX codec quality

Luiz Augusto von Dentz luiz.dentz at gmail.com
Wed Sep 19 06:04:32 UTC 2018

Hi Arun,

On Tue, Sep 18, 2018 at 9:02 PM, Arun Raghavan <arun at arunraghavan.net> wrote:
> On Wed, 12 Sep 2018, at 4:12 PM, Pali Rohár wrote:
>> Hello!
>> I would like to let you know that Serge from soundexpert.org did in last
>> month some research on aptX and its quality. Detailed article is on the
>> following website, specially see parts added around "August 2018":
>> http://soundexpert.org/news/-/blogs/audio-quality-of-bluetooth-aptx
>> ============
>> Conclusions:
>> aptX codec used in BT applications is no better than SBC at 328. Despite
>> slightly lower algorithmic delay of aptX both SBC and aptX codecs
>> provide the same 100-150ms latency in real-life BT applications.
>> If you hear the difference between SBC and aptX in some BT product,
>> there can be only two explanations - placebo effect or using SBC in
>> Middle or Low Quality modes.
>> AptX is just a copper-less overpriced audio cable.
>> aptX HD is high-bitrate version of aptX. It has clearly noticeable
>> increase in sound quality (not dramatic though taking into account the
>> increase in bitrate)
>> ============
>> And it just confirms my own testing. Whatever I did I was not able to
>> either hear or see difference between aptX and SBC encoded-->decoded
>> audio.
>> I had discussion with Serge and there are some ideas which Linux
>> Bluetooth A2DP software could supports:
>> 1) Allow user to specify SBC codec quality. In most cases, including
>> pulseaudio, SBC quality is chosen either to middle or low, not to
>> maximum bitpool. In some cases SBC at high quality can provide better
>> quality as aptX and more important -- SBC is supported by all headsets.
>> 2) Show user current SBC codec quality. So user would know what was
>> chosen and what should expect. I was told that Windows's Toshiba
>> bluetooth stack has support for this indication.
>> 3) In some cases SBC SNR bit allocation method can provide better
>> quality as SBC loudness method.
> Thanks for sharing, this is very interesting.
>> So then I could ask question:
>> 1) What to do with aptX? It is really useful for users to have it in
>> Linux & pulseaudio? Because it looks like that the only thing which it
>> has better is lower latency. But can pulseaudio on Linux system really
>> achieve it?
> What would prevent us from doing so?
>> 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?
> My preference is to not expose things to the user but try to move towards
>> 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.
> Right, could still be worth it indeed.
>> 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.
> In general, it seems the work to support other codecs could still be valuable for AAC and maybe in the future, LDAC? Is anyone aware of a similar comparison for the either of these codecs?
> AAC is still interesting for passthrough media, of course (I hope to have more on the ability to support that in coming weeks/months). Any objective information on LDAC would be interesting too.

Afaik Android supports LDAC so at least for headset/carkits using PA
that would be a good addition, though it requires even higher bitrate:


Luiz Augusto von Dentz

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