[linux-audio-user] [OT] recording levels (mismatch)

[Christophe Vescovi]

Erik Steffl a écrit :
>   I am trying to record from a receiver (not sure if that's the right 
> name, it's the amp/tuner, the thingy that all other components like CD 
> player, tape deck, video etc. connect to) and it seems like the levels 
> are too low (the soundcard is soundblaster live platinum, using alsa 
> drivers that come with kernel 2.6.5).
> 
>   the receiver has two stereo audio outputs - one is marked as tape deck 
> recording and the other one as VCR output but both seem to be about the 
> same (and there doesn't seem to be a way to change them). I connect them 
> to the RCA connectors on the front panel (live drive) but even if I set 
> the mixer to 100% (on line in) the levels are too low. On vu-meter the 
> levels only go to about 25-30% (max) while the 'normal' audio is 
> somewhere between 50-75%.
> 
>   I believe both the receiver and soundcard work OK (I can record from 
> receiver to tape deck, I can record to soundcard from other sources) so 
> I guess there's mismatch between the signal from receiver and what 
> soundcard expects. Is there anything I can do? do I need some pre-amp or 
> something? Seems crazy but does it make any sense to try to record from 
> speaker outputs? Is there any way to change what soundblaster expects on 
> input?
> 
>   TIA
> 
>     erik
> 

Using Google I was able to find the specification of the electrical 
inputs of the SBLive :
http://grassomusic.de/english/rauschen.htm
The Line In input impedance is 47K so it is unlikely a problem of 
impedance mismatch since the line out of your amp/tuner should have an 
output impedance of at least 1K. The Line in full scale output is 
however 1.5Veff. Since -10dBV = 0.32Veff and +4dBu = 0.775 Veff, 1.5Veff 
is quite a large value compared to audio standards but using alsamixer 
(or any other mixer) you should be able to adjust the input sensitivity.
Have you try using the Line In on the pci board instead of the one on 
the Live drive. There was issues regarding the Live Drive input with 
alsa drivers some time ago. I do not know if it has been fixed.
In any case you should consider using a preamp or a cheap console to 
adjust the levels since the SBlive level adjustement is done after 
Analog to Digital Conversion, a bad thing.

Christophe