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

Rene Herman rene.herman at keyaccess.nl
Tue Jun 10 01:37:05 CEST 2008

On 17-04-08 23:30, Rene Herman wrote:

>>>>> 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.
>> Can we narrow this down a bit please.
>> Run speaker-test -c2 -twav
>> Do the test to each sound card with alsamixer set to 0dB for most 
>> controls accept the master, and leave the master at a sensible setting 
>> for your setup so that you can hear sound at a sensible level
>> With the same dB values on the Andigy 2 and DMX, do you get the same 
>> loudness of sound output to the speakers?
> Very much not. Sorry, it seems the report (unsnipped above) got a little 
> confusing due to the followups but with everything at 0 dB on both DMX 
> and Audigy 2, the Audigy 2 is much louder and distorts.
> DMX has 'PCM' -34.5 --> +12 dB and 'Master' -46.5 --> 0 dB. I always 
> keep both at 0 dB for a good, comfortable level (adjusted further 
> externally).
> Audigy 2 'Front' and 'Wave' are both  at 0 dB (max) (everything default 
> in fact) and with 'Master' at 0 dB, it's much louder then the DMX. 
> Setting 'Master' to -16 dB (60) gets things the same.
>> I would like to find out if the problem is in the playback path, or 
>> the capture path.
> Playback I'd say and I personally consider DMX right here, due to the 
> distortion from the Audigy.
> Only introduced capture into the story above as "additional evidence" 
> where I could do a a comparison using only the Audigy itself and not the 
> DMX: with everything at 0 dB in the capture direction, a captured file 
> needs to be played back at -16 dB 'Master' to be equally loud to what I 
> hear _during_ capturing as well ("hear" from 'Analog Mix' at 0 dB). So I 
> get the feeling it's a simple matter of transposing 0 dB on the Master 
> scale for the Audigy (ie, new 0 dB is old -16 dB).
> I should have another emu10k1 driven card here somewhere. Is it useful 
> if I try to dig it up and see if the story's the same on it?

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