[alsa-devel] wrong decibel data?

Colin Guthrie gmane at colin.guthr.ie
Mon Jun 14 12:22:47 CEST 2010

'Twas brillig, and James Courtier-Dutton at 14/06/10 09:56 did gyre and
> On 14 June 2010 09:33, Colin Guthrie <gmane at colin.guthr.ie> wrote:
>> 'Twas brillig, and Raymond Yau at 14/06/10 01:25 did gyre and gimble:
>>> if your sound card have ac97 codec ., you can use audacity to record the
>>> output from hw:0,0 and you will see clipping occur when you set "PCM" volume
>>> above 0dB
>> So the standard response is "don't do that then" :)
>> That's why the base volume is shown to the user via GUIs so that they
>> can gauge the best point on the slider to use. Currently there is no
>> indication with alsa sliders at which point the 0dB "sweet spot" lies.
> What do you mean.
> If you use "alsamixer", dB values are shown so it is easy to find the
> 0dB "sweet spot".
> I think it is pulse audio that hides this information when it combines
> two alsa mixer controls into one pulseaudio control.

But it doesn't hide it. It's shown very clearly in the volume control
GUIs as the Base Volume.

Do you really think that most users look at the sliders to find the 0dB
point? Does gnome-alsa-mixer (the old one) expose this information? No.
Does kmix? No. So the vast, vast majority of users do not know where the
0dB point is unless they use alsamixer.... and even if the user is
advanced enough to use alsamixer, then I'd still say a proportion of
users are just looking at how far up the slider is rather than looking
specifically for 0dB.

So I'd argue the exact opposite of your claim. That with the base volume
clearly presented in the GUI, the h/w 0dB spot is much, much more
obvious to the vast majority of users.

I really think this is a vast improvement over a complex balancing act
of getting two different sliders setup to get distortion free audio!


Caveat: I've not yet made kmix show the base volume, so it still suffers
from the problem of masking this important information from the user.


Colin Guthrie

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
  Mandriva Linux Contributor [http://www.mandriva.com/]
  PulseAudio Hacker [http://www.pulseaudio.org/]
  Trac Hacker [http://trac.edgewall.org/]

More information about the Alsa-devel mailing list