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

Rene Herman rene.herman at keyaccess.nl
Wed Apr 16 17:37:03 CEST 2008

On 16-04-08 17:19, Rene Herman wrote:

For now last time that I reply to myself (promise):

> On 16-04-08 16:29, Rene Herman wrote:
>> On 15-04-08 16:33, Rene Herman wrote:

>> On that note, I just acquired an Audigy 2 (SB0240) that I'm testing 
>> with and now that I'm paying attention to it due to this thread -- its 
>> 0 dB setting is very significantly louder (with everything behind the 
>> line-out constant ofcourse) than the 0 dB setting on my TerraTec DMX.
>> James, I believe you are the emu10k1 person? Data:
>> TerraTec DMX = ESS Canyon3D (ES1970MS-3D) + Sigmatel STAC9704T
>> Creative Audigy 2 (SB0240) = Creative CA0102-ICT + Sigmatel STAC9721T 
>> (+ Crystal CS4382-KQ which seems to provide digital attenuation as well)
>> At 0 dB master the Audigy 2 is much louder than the DMX is and audibly 
>> distorts. Judging by hearing, keeping the master at -16 dB (60 in the 
>> integer scale) gets things about the same. Was that scale provided by 
>> datasheet or just guessed? Especially the distortion would seem to 
>> indicate that something is actually doing analogue amplification at 
>> the 0 dB ALSA setting...
> Expanding, with the 'Line' control at 0 dB (74 integer) and 'Analog Mix' 
> at 0 dB (100 integer) everything does sound right with both 'Master 
> Capture' and 'Master' at  full, and too faint with 'Master' at -16 dB. I 
> guess this indicates that it's something at the DSP side only? (sort of 
> loosing my way in this bewildering array of controls so if I need to be 
> guided to possibly say sensible things -- please do)

When I do actually capture, -16 dB master is again the correct setting when 
playing back (with everything else still set to 0 dB as described above). 
It's then equally load as when directly monitored during recording. I expect 
then the Master dB scale needs to be adjusted down? If yes, I'll try to make 
very, very sure that -16 dB now is the correct new 0 dB.


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