Installation guide
Chapter 7: Calibrating the 888/24 I/O 53
chapter 7
Calibrating the 888/24 I/O
Before you use the 888/24/I/O Audio Interface,
you may want to calibrate its input and output
levels to the level of your mixing console.
The 888/24 I/O is factory-calibrated so that its
input operating level is set to +4 dB nominal
with 18 dB headroom nominal at full code,
unity gain, making calibration unnecessary for
most professional applications.
If you do need to recalibrate your interface or
other components of your studio, you can use
the alignment procedure described in this chap-
ter.
About Calibration
Calibrating levels on a digital recording device is
different from calibrating levels on an analog re-
cording device. Unlike analog devices, most dig-
ital devices do not have a standard “0 VU” level
setting that corresponds to nominal input and
output levels. Instead, with an interface such as
the 888/24 I/O, the meters are calibrated in deci-
bels below peak (digital clipping) level.
Headroom
The concept of headroom is slightly different for
analog and digital devices.
Analog Most analog devices allow for a certain
amount of headroom above 0 VU. If you send a
signal above 0 VU to an analog recorder, you
still have a margin of headroom, and if tape sat-
uration occurs, it does so fairly gracefully, giving
the audio a compressed sound that some find
desirable.
Digital Digital devices, on the other hand, do
not allow for signals that exceed the dynamic
range of the input. When a signal exceeds the
maximum input level for a digital device, clip-
ping occurs, causing digital distortion, which is
harsh and usually undesirable.
The AES Standard for Headroom
The AES (Audio Engineering Society) standard
for headroom is currently –18 dB for nominal
level in a digital audio system. The exact value
you use will be determined by the amount of
headroom available in the rest of your system.
For example, if your mixing console has 15 dB
of headroom above nominal level, then you
may want to calibrate the 888/24 I/O to have
15 dB of headroom.
TDM_Install.book Page 53 Saturday, January 13, 2001 9:35 PM