2010/2/16 Lennart Poettering <mznyfn@xxxxxxxxxxx> > Heya, > > a while back I wrote a little tool "dbmeasure" which can be used to > determine dB attenuation data for alsa mixer controls. I have now > extended this little dB tools suite to include a tiny tool "dbverify" > that can be used to verify the correctness of existing dB data exposed > by the drivers. It should be relatively easy to use that tool, > suitable even for non-guru folks who want to debug the dB information > from alsa. > > http://git.0pointer.de/?p=dbmeasure.git > git://git.0pointer.de/dbmeasure.git > > Just run "make" in a git checkout and then try: > > $ ./dbverify Aureon51MkII Master 30 200 > > That will verify the dB data of the "Master" control of the sound card > that goes by the id "Aureon51MkII". It will compare the discrete > volume steps 30 and 200: first it will play a full amplitude sine wave > at mixer volume step 30, and then will change to mixer volume step > 200, but attenuate the sine wave in software compensating for the > volume change. So once you hear the sine wave attenuated by the hw, > and once by the software. If the card's dB data is correct both sines > should have the same volume. > > Now, playing around with this, I could verify what I already mentioned > to Jarsolav elsewhere earlier: it seems that particularly USB cards > seem to expose invalid dB data (at least all mine do). For example, > for the above mentioned Aureon 5.1 it's really *way* off -- if you > posess that card just run the line above, and listen to the > difference. It's really bad. OTOH the dB data of the HDA cards I own > is pretty accurate as it seems, at least I was unable to decide just > by listening which sine wave was attenuated by sw, and which by hw. > > Getting back to the invalid dB data from the USB cards: the question > is whether the USB descriptor data is badly parsed, and the dB > mismatch hence systematic for USB cards, or if these cards are just > crappy and include invalid data? In which case I wonder what we could > do about that? The Aureon's dB range already looks suspicous, since > both the max and the min dB value are < 0 (-47.69 to -1.97), so maybe > we could add some heuristics to filter out data that already looks > suspicous? > > Invalid dB data from the driver is a real problem for the "flat > volume" logic in PA. We basically allow each app to control the full > hw volume range individually, and then set the hw volume to the max of > what all apps wanted and attenuate the other streams accordingly. On > the Aureon this doesn't work at all, since the attenuation of the > streams is miscalculated due to the invalid dB data. > > Lennart > > Refer to README WHAT YOU NEED? a) A sound card where input and output are synchronous b) A feedback cable that allows you to feed sound card output how do I know my sound card support synchronous playback and capture ? do you program able to find out whether the sound card support synchronous playback and capture ? do your result still valid if the sound card does not support synchronous playback and capture ? do the result different if I use analog loop back of the ac97 codec instead of a loop back cable ? _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
