[alsa-devel] Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII

Mark Brown broonie at opensource.wolfsonmicro.com
Wed Feb 17 14:06:23 CET 2010

On Wed, Feb 17, 2010 at 11:55:17AM +0000, James Courtier-Dutton wrote:
> On 16 February 2010 23:56, Lennart Poettering <mznyfn at 0pointer.de> wrote:
> >
> > The reason I was asking how Jaroslav chose the 0dB position for his
> > measurements was purely because I wanted to do my own measurements for
> > that Aureon card. The dbmeasure tool I wrote for stuff like that puts
> > 0dB at max amplification, however Jaroslav didn't, so I was wondering
> > how he chose 0dB then.
> >
> > Lennart
> >
> I think the digital side is clear. So I will not go into that.
> I think we need to separate the analogue side into a number of categories:
> 1) Standard consumer line-out levels.
> 2) Standard pro line-out levels.
> 3) Consumer line-in levels.
> 4) Pro line-in levels.
> 5) Consumer mic levels.
> 6) Pro mic levels.
> 7) Consumer speaker levels.
> 8) Pro speaker levels.

There's also headphones there, though for both speakers and headphones
it's questionable if we want to do anything.

> On the analogue side, I believe the 0dB gain point is intended to be
> the point at which one can be fairly sure that the distortion will be
> low for a sensible full scale input.

Generally 0dB is pass through (which does also tend to be the optimal
performance point).  Actual expected gain levels will vary depending on
application - for example, a microphone input will usually need an
amplifier with fairly high gain in the path to get the signal to a level
usable by the rest of the system.

More information about the Alsa-devel mailing list