On Wed, 17.02.10 13:55, James Courtier-Dutton (james.dutton@xxxxxxxxx) wrote: > So what you want it this. > Example 1: > If there are 2 gain controls between the CPU and the line-out. > A is at 0dB > B is at 0dB > > If one changes A to +3dB and B to -3dB and one was playing a quiet > sound (so no distortion), the result should sound very similar, volume > wise, to the original 0dB, 0dB state. Exactly. > Example 2: > There is one gain control between the CPU and the line-out that we are > interested in. > A is at 0dB. > > If one changes A to +3dB and at the same time modify the source signal > digitally by -3dB, the result should sound very similar, volume wise, > to the original. Exactly. And this second case is what dbverify from my little tool set verifies. > You would have to build your test tool so that it would detect > distortion as well as levels.This way you could also find out where > the limits really are in the chain. I am not sure I want to get lost in complexities like that. My simplified world where all elements in the pipeline are perfect, linear multiplicators is oh so cozy, that I am happy to keep my eyes shut and ignore that the actual filters implemented in the various elements might be vastly more complex. In fact dbmeasure and dbverify pick a 440Hz tone for their tests, so all the volume factors I measure and rely on focus on one point in the frequency spectrum and leave it at that. Of course, this is a drastic simplification, but it should be good enough on most cards and for desktop audio. > This is a good aim, but I still think getting the correct 0dB points > is more important to ensure the best audio quality. > I personally think that PA should just set the hardware ALSA controls > to 0dB and do all the volume control in software within PA. > The 0dB points in hardware should result in the best sound quality. I don't think this would be a good idea. In a lot of hardware you definitely want to make as much use of the built-in volume adjustment capabilities as you can. For example, on my integrated USB speakers you may control the built-in amplifier with the alsa mixer, and that's definitely much better than attenuating the 16bit PCM stream and having the USB speakers amplifier constantly configured to a very high volume level. Lennart -- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net http://0pointer.net/lennart/ GnuPG 0x1A015CC4 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
