On Jun 14 11:37:52, Paul M wrote:
> I have a large amount of analog audio I need to digitize and
> naturaly want to ensure best transfer quality. So I need to set
> the analog level at the input to the adc as high as possible
> without clipping.
It is good practice to leave a little headroom (say, 6dB)
for further processing. You might want to do some noise
reduction, compressing, whatever, and the effects will clip
if the signal already is saturated.
Also, "the input to the adc" is not all there is to it;
there are other mixer settings that affect the signal
that will eventually end in your file.wav
> Ideally, I'll get the workstation hardware
> set to certin defaults, then adjust the incomming audio as
> required.
There are no "defaults". Your analog inputs can
(and most probably will) vary greatly.
> This leads to a couple of questions:
> Are there (typicaly) any variable gain stages in the analog input
> path in the computer.
Yes. 'mixerctl -a' will shouw you how the azalia 'widgets' are
interconnected on your codec.
> Mixerctl -av (full output below) shows a
> node called 'record.adc'. It seems reasonable that this might
> opperate on the analog input to the adc. However there is also
> 'record.volume', though I would assume this operates on the mixed
> digital signals at the end of the chain.
record.volume
Amplifier gain control for widgets listed in record.volume.slaves.
> Also: a lot of the gain stages have defaults of 120.120. Would
> it be reasonable to assume that this is the 0 gain setting?
What's a "0 gain setting"?
I believe Jacob Meuser has work going on to make the numbers
on the azalia knobs correspond to actual decibels,
but I don't know if it's current yet.
> bios0: ASUSTeK Computer INC. P5QPL-AM
> azalia0 at pci0 dev 27 function 0 "Intel 82801GB HD Audio" rev 0x01:
> apic 2 int 21 (irq 5)
> azalia0: codecs: Realtek/0x0887
> audio0 at azalia0
It would be my guess that this is the audio chip that's integrated
with the Asus P5QPL-AM motherboard. If you are really after "best
transfer quality", you might want to use something else in the
first place.
