That darned -10, +4 thing again. An excerpt from a recent, very frustrated inSync reader:
“I have a Pro Tools Mix system. My master is at unity in Pro Tools. I have two channels coming out of an 888 interface into a 4-bus Mackie board via the 1/4” line in. The signal is way too strong for the board. In order to keep the board from distorting I have to pull the Pro Tools master down to -14, and even then it is almost pegging. The Mackie trim controls are all the way down and the faders are at unity. Do you have any idea what could be causing this?”
Why yes I do. At least you are one step ahead of the guys who plug into the XLR microphone input on their mixers. The problem is that the 888 interface is set up to send and receive signals at the +4dBu reference level, but the Mackie’s line input is designed for a -10dBV line level reference. Turning the output level down on the Pro Tools system solves the distortion and overload problems, but the digital resolution goes way down when you do that, which means the available dynamic range is limited. You need to match the levels between the output and input device. Handily the 888 interface has internal jumpers that allow you to change any of its outputs to a -10dBV level. Once you do this you will find that the level is much more agreeable to the Mackie.
One other problem, however, is that even though your PT fader is at unity gain, you may still be outputting a signal that is significantly hotter than the reference level. This is a function of the fact that most people working with digital audio record and mix at the highest possible levels (because that is where distortion is the lowest in digital). They try to keep their peaks as near as possible to full code, which results in a very, very hot signal. One that will make meters go into the red even if the levels of the analog equipment are matched. For more background on this issue, check out the TTOTD from inSync issues 4/10/97 and 12/9/98.