Specifications

HD I/O Guide6
Loop Master LED
The LOOP MASTER LED indicates which audio
interface is the master peripheral. The Loop
Master LED will be continuously lit on the cur-
rent Loop Master peripheral only, and unlit on
all other peripherals. (Only one Avid HD periph-
eral can be Loop Master at a time.) The Loop
Master LED will always be lit with a single inter-
face.
With HD Native hardware, Loop Master defaults
to the first audio interface connected to Di-
giLink Mini Port 1 on the HD Native card.
For Pro Tools|HD systems, Loop Master defaults
to the first audio interface connected to the pri-
mary, or “core” Pro Tools|HD card. On
Pro Tools|HD (for PCIe), this is the Accel Core
card. On Pro Tools|HD (for PCI), this is the HD
Core card.
Sync Mode LEDs
The SYNC MODE LEDs indicate the current
Clock Source as set in Pro Tools.
INT (Internal) Indicates the HD I/O sample clock
is generated by its internal clock, as determined
by the session Sample Rate.
DIG (Digital) Indicates that an external
AES/EBU, TDIF, Optical (ADAT), Optical
(ADAT S/MUX), or S/PDIF device is providing
system clock. If no valid clock source is de-
tected, HD I/O will switch to internal clock, the
DIG LED will flash, and an error message will
appear on-screen in Pro Tools.
LOOP Indicates that the HD I/O is slaving to an-
other Avid HD audio interface or SYNC periph-
eral using Loop Sync.
EXT (External) Indicates that the HD I/O is using
the EXT CLOCK IN port for system synchroniza-
tion.
When synchronized to Word Clock, External
Clock input and output do not have to be at the
Word Clock rate. EXT CLOCK IN synchroniza-
tion will typically be 1x the current session sam-
ple rate. However, for sample rates higher than
48 kHz, HD I/O generates a choice of 1x, 2x, or
4x of a base rate of 44.1 kHz or 48 kHz, as
follows:
Meters
These four-segment LEDs indicate signal level
for each of the sixteen channels. The top row
of meters indicates input levels, and the bottom
row shows output levels. These meters are
calibrated at –42 dB, –18 dB, –6 dB, and 0 dB,
respectively.
Session Sample Rate Word Clock Support
44.1 kHz 44.1 kHz
48 kHz 48 kHz
88.2 kHz 88.2 kHz
44.1 kHz
96 kHz 96 kHz
48 kHz
176.4 kHz 176.4 kHz
44.1 kHz
192 kHz 192 kHz
48 kHz
Note that 0 dB is not to be confused with
clipping; use the on-screen meters in
Pro Tools to determine whether a signal is
clipping.