[linux-audio-dev] ALSA features.

[Jussi Laako]

On Sat, 2005-09-03 at 21:14 +0100, Dan Mills wrote:
> I don't think this is right, a signal **level** can be measured against a 
> known reference level, and for metering it is important to know what this is, 
> but a **gain** value is **always** unitless (You are multiplying a signal 
> which has units by a scalar value).

The thing here, is that I would like to know which actual output level
results when some given sample value is written with some gain setting.

Or I could determine actual input level by reading sample value and
input gain setting.

Now, if the mixer adjustment is just 0-100% of unspecified gain range,
this is rather hard. If it's in dB, it is possible if there is some
relation of the gain with some actual level. ie. 0 dB gain would mean x
dBu output level.

For example, with some industrial A/D and D/A card's I'm able to
calculate actual sound pressure at microphone when it's sensitivity vs.
frequency is known. Or to know how to get exactly 1Vpp output level.

With my M-Audio Delta1010 this is rather easy, as there are no
adjustable analog gain stages and it can be calibrated. But trying to do
this generally with any sound card is pretty hard.


-- 
Jussi Laako <jussi.laako at pp.inet.fi>