Apogee AD-8000 Application Notes page 2

Soft Limit calibration procedure using test bench gear
You will need:
An Oscillator or tone generator capable of delivering 1 kHz up to about +20 dBu.
An analog-reading meter capable of reading +20 dBu (any good quality high impedance volt
meter will do, but you will have to do the conversion from voltage to dB. We recommend the
Fluke 8060A (found in most studios) as it is extremely accurate and will read out in decibels,
which makes all of this much easier.)
A 3-way mult (parallel) on your patchbay – one in and three out.
1. Calibrate the AD-8000 to your specific requirements. Turn Soft Limit OFF.
2. Mult the output of the oscillator to two inputs of the AD-8000 and to the meter. Adjust the
oscillator output level until the red OVER LEDs light, then back it off until the LEDs just go
out. Make a note of this level on the meter. If you have an 8060A, just hit the REL (relative)
button.
3. Increase the oscillator level by +4dB on meter (see procedure using a recording console step 5
for information about changing the threshold).
4. Turn Soft Limit ON.
5. Adjust the Soft Limit adjustment pots (inside the AD-8000 – see above) until the OVER LEDs
just go out. Verify that you are not getting any "overs" on a DAT machine or a digital-
reading meter.
6. Return to your "normal" operating set-up.
"+4" dBFS
0 dBFS
-4 dBFS
NOTE: There is no such thing as "+4 dBFS". This means that the analog input level is 4 dB over the analog input level that translates
into 0 dBFS (full scale). So, for example, if the unit is calibrated to +4 dBu = -16 dBFS, then an analog input of +20 dBu would produce
a full scale input with SOFT LIMIT set to OFF. With SOFT LIMIT ON, this top level would be an analog level of +24 dBu. Thus, with
SOFT LIMIT ON, the unit would produce a 0 dBFS light with an analog input of +24 dBu.
Apogee Electronics Corp
"0" dB LED w/ SOFT LIMIT ON
"0" dB LED w/ SOFT LIMIT OFF
SOFT LIMIT THRESHOLD
Calibrating SOFT LIMIT
limiting "window"
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