On Tue, Apr 15, 2008 at 03:43:30PM +0100, James Courtier-Dutton wrote: > John Rigg wrote: > >>On Monday 14 April 2008 23:07:22 James Courtier-Dutton wrote: > >> > >>>The aim of the dB values in the ALSA mixer is this. > >>> > >>>For Playback: > >>>Set all the mixer controls to 0dB. > >>>Send a sample digital signal from the CPU to the sound card. > >>>The measured analog signal on the line-out should be the same for ALL > >>>sound cards. > >>> > > > >The dB setting in a mixer refers to gain, not level. > >Expecting the same absolute level from pro and consumer > >sound cards at the same gain setting is a little ridiculous. > >If I set a control at 0dB I want just that: 0dB gain. > > > >John > > > But surely it is a bit more than that. > If I work with Pro gear and I capture some sound via line-in. > I then send the digital sound file produced to another person who also > has pro gear. > When they output that digital sound file to their line-out, it should be > identical, level wise, to the captured line-in was so long as both > people have the same dB gain levels set. > In this case, we would need some way to convert Volts from the line-in > to specific digital samples in the sound file. > I have not been able to find out what this conversion should be. > E.g. a 16bit signed digital sample with value +5000 equals X Volts > output from line-out. > What is that X value? In pro gear, levels are referenced to digital full scale in the A-D and D-A converters. The actual analogue signal voltage level that corresponds to this varies between interfaces. In most pro converters, full scale corresponds to about +20dBu (about 11 volts peak) but there is some variation (+/- 2 or 3dB) between manufacturers. I'd expect the line in and line out levels on a consumer sound card to be much lower than this, so obviously the same standard can not be applied to both. John _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
