[LAD] Calibrating sound cards

[James Courtier-Dutton]

Hi,

Is there a recognized method for calibrating a sound card?
e.g.

For Playback, one sends a sample .wav PCM file to the sound card, then 
measure the analog output from the line-out.

If the sound card itself provides 0dB of Gain, what should be the 
measured figure?

Can this be done with a simple AC volt meter?

There seems to be some debate, with regards to ALSA, as to whether the 
line-out is at the correct level if one sets all the ALSA mixer controls 
to 0dB.

James