[linux-audio-user] Low Input Level
st at tobiah.org
Sat Dec 4 20:48:14 EST 2004
The Delta cards have two controls for each channel that
affect the input level seen on the meters. The one that
is most often seen is a simple volume control, which is
analagous to the fader on a mixing console. The other
one is more like the 'trim'. It is a control that adjusts
the actual gain, or amplification power of the input.
Using envy24control, these sliders can be seen under the
'Analog Volume' tab. The ones called 'ADC 0'... 'ADC n'
are the volume controls, and the ones called 'IPGA 0'...
'IPGA n' are the *gain* controls.
Knowing the difference is very important with regard to
getting a clean recording. Basically, turning up a gain
control results in the amplifier generating more noise
along with a louder signal. If it is set too low however,
then the signal may not reach full level, and will suffer
from a poor signal to noise ratio.
An easy way to look at this, is to always leave the volume
(ADC) controls all the way up (Why reduce what you have
already amplified?) and then to use the gain (IPGA) controls
to bring the level up near 0dB. This will result in the
cleanest properly adjusted signal.
Now under Windows, a slider for the IPGA is not provided.
There is only more limited access to the gain registers,
allowing the inputs to be set for +4, 0, and -10 dB use.
This was done, I imagine, to prevent someone from turning
the gain up high, with the volume down, resulting in a
Fortunately, the wise programmers of ALSA gives us the
hardware's full range of control (256 steps I believe
for this register) for the gain. Pushing both the ADC
and IPGA sliders all the way up, gives a level of
sensitivity that far surpasses (well, is higher) then what
can be accomplished under windows. Some experimentation may
be needed to find the best setting; the amps on my Delta 44
are pretty clean, even at high gain levels. If a noisy
mic pre is being used, it may be best to turn *it's* gain
down and lean on the Delta amps. If a great mic pre is
being used, then it may be best to raise it's gain, and
back off on the Delta's.
David Cluytens wrote:
> Hi, I've got the following problem with a M-AUDIO Delta 1010 card.
> This card uses an ICE1712(envy24) chipset.
> When i insert a 5khz sinus of about 0,4V Um on Capture channel 1 under
> windows. I see that in the mixer pannel all green lights are lid.
> But when i do the same test onder linux based upon the alsa drivers, libs,
> utils version 0.98 to 1,07.
> I only see 1/3 to 1/2 of the signal under the envy24controll mixer.
> I've done this test with 3 different sound cards 2 rev C and 1 rev D card.
> I've tested the input level on a 6 card, which is working fine under linux
> with alsa driver 0.98 and there the input level matches the input level under
> our windows system.
> Tests i Allready did
> Playing with the sliders of the envy24control mixer.
> Trying a new soundcard.
> dumping and restoring the asound.state file of a working card with alsactl
> Switching the hard drive of working system with a not working system, this
> actualy made the problem worse, since i now have two system where the card
> ain't working under linux but works fine under windows.
> So, My question now.
> How do increase the input level gain of the M-AUDIO DELTA 1010?
> David Cluytens.
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