Setup guide
Chapter 3: Installing Pro Tools on Mac 31
To connect Digidesign Legacy I/Os:
1 Connect the “MIX card” end of the peripheral 
cable that came with your Legacy I/O (60-pin 
side) to the Legacy Port on the primary 
Pro Tools|HD audio interface. Connect the other 
end to the Computer Port on the Legacy I/O. 
2 Do one of the following:
• Connect any additional Legacy I/Os in the 
same manner, to Pro Tools|HD audio inter-
faces connected directly to Pro Tools|HD 
cards.
– or –
• If you are using a Y cable (Legacy 16-chan-
nel peripheral cable adapter), connect this 
to the Legacy port first, then connect the 
audio interface peripheral cables to Port A 
and Port B of the Y cable.
3 To properly clock the Legacy I/O, connect the 
Ext. Clock output port on the Pro Tools|HD I/O 
to the Slave Clock IN on the Legacy I/O. The 
Legacy I/O will switch to Slave mode once the 
proper clock is outputting from the 
Pro Tools|HD I/O. Always use the Ext. Clock Out 
port of the same I/O to which the Legacy I/O is 
attached.
If you are using the Y cable to connect multiple 
MIX audio interfaces, you must also connect the 
Slave Clock Out of the first Legacy interface to 
the Slave Clock In of the second Legacy inter-
face with the provided BNC cable. You cannot 
clock more than two MIX audio interfaces from 
a single Pro Tools|HD audio interface. 
If you have a third MIX audio interface, supply 
its 256x clock from the Pro Tools|HD I/O to 
which its 60-pin cable is attached (either your 
second audio interface, or directly to an 
HD Accel or HD Process card).
Optional 16-channel peripheral cable adapter
“A” to first
Legacy I/O
“B” to second
Legacy I/O
To Legacy Port on
Pro Tools|HD audio interface
To ensure the proper functioning of Legacy 
I/Os (such as an 888|24 I/O or 
882|20 I/O), launch Pro Tools and initial-
ize the Legacy I/Os in the Hardware Setup 
dialog before turning them on (See “Config-
uring Legacy I/Os” on page 54). Then quit 
Pro Tools and shut down your computer. 
When relaunching your Pro Tools system, 
turn on your Legacy I/Os first and allow 
them to complete booting before turning on 
your Pro Tools|HD audio interfaces, and 
then your computer.
Before you turn on and configure your Leg-
acy I/Os, turn down the volume of output 
devices. Very loud digital noise may be 
emitted before the Legacy I/O is initialized.










