On Wednesday 12 September 2018 19:03:41 Luiz Augusto von Dentz wrote: > Hi Pali, > > On Wed, Sep 12, 2018 at 1:42 PM, Pali Rohár <pali.rohar at gmail.com> 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. > > > > 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? > > I don't think, not the level of latency necessary for speech and to > avoid lip sync issues, so that would leave aptX at the same category > as SBC. That is what I thought. So seems that aptX (non-HD) has no benefit over SBC in pulseaudio. > > 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. So... seems that maximum value is 53: https://cgit.freedesktop.org/pulseaudio/pulseaudio/tree/src/modules/bluetooth/bluez5-util.c#n1599 https://cgit.freedesktop.org/pulseaudio/pulseaudio/tree/src/modules/bluetooth/bluez5-util.c#n1260 Even when headset advertise higher value. Should not we increase when headset support higher value? Also question about allocation method SNR vs loudness. Default is loudness. > > 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. Ok, I would let this part to other people as currently I do not have aptX HD native hardware. > > 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
