Subject: Re: [linux-audio-user] [OT] recording levels (mismatch)
From: Christophe Vescovi (vescovi_AT_lpsc.in2p3.fr)
Date: Wed Oct 13 2004 - 10:24:02 EEST
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
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