888/24 I/O
20
The Calibration Process
Analog
To calibrate the input level of an an-
alog device to a mixing console’s output
level, you would typically send a 1 kHz
tone at 0 VU from the console to the ana-
log deck and align the recording deck’s
meters to read 0 VU.
Digital
With a digital recording device such
as the 888/24 I/O, however, in order to al-
low for headroom, you must align a 0 VU
tone from the console to a value less than
zero on the 888/24 I/O, by exactly the
amount of headroom that you want.
For example, to have 12 dB of headroom
above 0 VU with the 888/24 I/O, you must
align the incoming 0 VU 1kHz tone to a
level of –12 dB. For 18 dB of headroom,
you would align it to –18 dB. (Since it is as-
sumed that you are using the 888/24 I/O
with a +4 dBu console, a 0 VU signal level
coming out of the console is actually equiv-
alent to a n4 dBu level signal.)
Calibrating The 888/24 I/O
If you are using Pro Tools 4.3.1 or earlier,
you can use the Calibration Tool applica-
tion (available on your Pro Tools Installer
CD-ROM) to calibrate the outputs and in-
puts of the 888/24 I//O.
If you are using Pro Tools 5.0 or later, refer
to Appendix B: Calibrating the 888/24 I/O
(Pro Tools 5.0) for calibration instructions.
The Calibration Tool software
The Calibration Tool has the following
controls:
Channel
Use this pop-up to select the input
channel for the input level readings.
Input Level
Use this as a graphic and nu-
merical display of the dB level relative to
the headroom you have specified on that
particular interface. (In other words, the
amount of dB below digital clipping, or the
amount of analog headroom you wish to
use in your system.)
Signal Present
This indicates when a
–60 dB signal relative to the headroom is
present at the input.
Headroom
Use this field to enter an amount
of headroom between your 0 dB level and
the 888/24 I/O full scale digital value. Any
values above the full scale digital value will
cause digital clipping.
Oscillator
Use this to turn the audio wave-
form generator on or off.
Frequency
Click on this pop-up to select
the output frequency of the audio wave-
form generator. You can choose a 100 Hz,
1 kHz, or 10 kHz signal.
