No subject

control at the analog terminals of the card. This is the Level control,
and it specifies the absolute voltage at the output for full scale
digital signal (and intermediate Volumes set to 0dB)

It has units of dBu http://en.wikipedia.org/wiki/Decibel#Voltage.
(It might as well be dBV or any other reference dB measurement).

For our cards this is adjustable, but lets say for consumer cards it is
fixed.  This information is not currently available via the ALSA API.

A hypothetical example.
[DAC>---[Variable gain>---[amplifier>---[output jack]

Lets say
the DAC produces 2Vpp (6dBVpp) for fullscale digital input (0dBFS)
and the amplifier has 6dB gain.
and the variable gain is from -40dB to 0dB
and the units of the reference level are dBVpp

Combining these we represent the DAC + gain + amplifier as a single
Level control with units of dBVpp and range -28dBVpp to +12dBVpp

or equally valid, could represent it as
a Volume with range -40dB to 0dB followed by a
a fixed level of +12dBVpp

or equally valid, could represent it as
a Volume with range 0dB to +40dB followed by a
a fixed level of -28dBVpp

i.e. the 0dB position is arbitrary, related to what is chosen as the
output reference level.

The fixed level information, would be attached to some representation of
the output connector.

Clear as mud?

regards

Eliot Blennerhassett
http://www.audioscience.com