1 March, 2005
V1682OPMA.doc
Page 27 of 32
8.3 ANALOGUE
AUDIO
SUB-MODULES
The audio sub-modules with analogue interfaces, both inputs and outputs, need to be calibrated. This
operation is to ‘trim out’ the small errors in the components.
The ADC and DAC sections are adjusted separately, but if an A-A module is fitted then the DAC
adjustment should be done first.
The calibration values relate directly to the sub-module and not the main board, and they are stored on
the sub-module itself. This means that there is no need to re-calibrate a sub-module if it is moved from
one board to another.
8.3.1 DAC
By turning Calibrate Mode ON and selecting one of the DAC sub-menus the unit will automatically
generate tone with an MAL of +18dBFS.
To calibrate the frequency set the unit to generate Tone by turning Cal Mode ON and selecting one of
the DAC sub-menus.
CALIB
Cal Mode
Cal On
Connect the outputs in turn to a high quality analogue audio analyser and adjust each of the four
channels for 0dBu on:
CALIB
DAC A(L)
CALIB
DAC A(R)
CALIB
DAC B(L)
CALIB
DAC B(R)
8.3.2 ADC
There is no need to change the internal settings to calibrate the ADCs, so it is not necessary to turn
Calibrate Mode ON.
Connect the inputs from a high quality audio generator to the inputs at +16dBu and the outputs to an
analyser. Set MAL to +18dBFS, and adjust the level +16dBu.
CALIB
ADC A(L)
CALIB
ADC A(R)
CALIB
ADC B(L)
CALIB
ADC B(R)
