On Tue, Mar 13, 2012 at 3:48 AM, qduaty <qduaty@xxxxxxxxx> wrote: > 2011/10/18 Siarhei Siamashka <siarhei.siamashka@xxxxxxxxx>: >> Still I would suggest you to try the attached patch just for a test. >> It reduces audio volume as part of the sbc encoding process and should >> eliminate most of the possible clipping cases on the decoding side. > > Sorry for responding after a half year :) but I finally tested your > encoder patch applied to libbluetooth version 4.96, using AIMP3 and > pulseaudio. Unpatched encoder produces a "digital" distortion (which > is rather annoying) and sounds much like BlueSoleil on Windows. After > patching, music is slightly quieter (which can be expected if you > decreased its volume) and has an "analog overdrive" like through a > cheap FM radio. Anyway, the annoying "digital" distortion that was > present in unpatched encoder, is now gone. Thanks for testing! One more experiment would be very much welcome. I wonder if just defining SBC_HIGH_PRECISION without doing anything else would have any noticeable effect on audio quality in listening tests. > Some fluctuations can be heard in higher bands in classical music, and > (as expected) instruments are indistinguishable, but it's acceptable > given the low bitpool. > > For the "analog overdrive" I hear, it may also come from the device > itself (its proper name is Nokia BH-503). Considering its glue sealed > case, it might have been designed as a budget solution and its price > was "adjusted" due to no competition. > >> Using bitpool 128 is kind of weird for SBC codec, because the encoded >> data stream has about the same size as the the original data and this >> defeats the whole purpose of having any lossy compression at all. > > Yes, but who needs a lossy compression in an endpoint? SBC and MP3 > were introduced to overcome the low throughput problem of the > bluetooth link, which is no longer the case since 2.0+EDR has plenty > of unused bits. > >> I still recommend you to try sbcenc/sbcdec tools for the experiments with audio quality. > > I tried them some time ago, but I believe ALSA backend may serve for > the same purpose (and is much easier to use). 8 blocks seems to sound > slightly better than 16 for classical music, full stereo eliminates > the floating of virtual sound sources, 48 kHz also seems to increase > quality a bit when compared to 44.1. sbcenc/sbcdec tools can do file-to-file encoding/decoding and eliminate the need to use any bluetooth device (which could potentially be the source of some audio quality issues). However, as I mentioned before, audio quality in the current bluez sbc decoder is far from perfect and the synthesis filter needs to be replaced first. -- Best regards, Siarhei Siamashka -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
