[alsa-devel] What does 0dB refer to? (Logitech USB Speakers)

[John Rigg]

On Sat, Apr 12, 2008 at 08:26:49PM +0100, James Courtier-Dutton wrote:
> Florian Faber wrote:
> > On Saturday 12 April 2008 20:14:44 James Courtier-Dutton wrote:
> >   
> >> That sounds reasonable for now. Professional sound card users will
> >> maybe just have to remember to mute the master control before
> >> connecting their speakers.
> >>     
> >
> > This is very, very dangerous - not only can it harm the equipment, it 
> > can also harm the user. 0dBFS equals >121dB at a distance 2m away from 
> > my head, and I have a *small* setup.
> >
> > To be honest, I think I would then insert a switch in the RME driver 
> > that will enable the outputs only after the RME mixer application has 
> > been started.
> >
> >
> > Flo
> >   
> 
> Thats not very helpful really.
> What value should we set it to then?

Minimum gain. On the aforementioned RME mixer, setting all the channels
to anything other than that would make it unusable.
Pro cards with high channel counts are very different from consumer
cards, and their users have totally different requirements. Is it
really a problem to accomodate both classes of card/user?

> Another alternative could be to leave everything at 0dB except the master.

With 64 channels, that is likely to cause massive clipping
even if damage is prevented by keeping the master down.
The usual use case here would be to just turn up the required
channels. Having to turn all the rest down manually would seriously
disrupt work flow. No studio client would be happy about this.

> For the master we could select say minimum dB + 12.
> So, if the Master ranged from -70 to 0 dB, we would set Master to -70 + 
> 12 = -58dB.
> 
> Would that suit everyone better.

That would be reasonable for consumer cards. Pro sound cards should
never initialise themselves to anything other than minimum gain.

John