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

Takashi Iwai tiwai at suse.de
Tue Apr 15 12:17:18 CEST 2008

At Fri, 11 Apr 2008 22:46:11 +0200,
Lennart Poettering wrote:
> Now the thing is, this mostly works fine, however on one of my
> devices, a pair of external Logitech USB speakers (ID 046d:0a04
> Logitech, Inc. V20 portable speakers), the dB scale seems to be
> totally bogus. According to ALSA volume ranges from -41 dB to
> +3dB. However, Every setting > -41 dB makes audio awfully
> loud. Really, really fucking loud that is. Disco loud. As loud that
> the speakers start jump around centimeters due to the massive
> vibrations. Setting the volume to 0dB with those speakers really makes
> you fear you are trashing them.

This is typically a problem of your usb hardware.  The USB descriptor
gives the dB level information and the usb-audio driver simply passes
the given data as dB scale information.  But, the hardware actually
doesn't behave as it states.  Unfortunately a frequent problem with
cheap USB audio devices.

So, it's definitely no universal ALSA problem.  Please don't mix up.


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