Input Connections and Audio Levels
Avid HD audio interfaces operate as line-level devices and offer no pre-amplification. Low-level sources like microphones and electric guitars need to be pre-amplified. You can do this with a quality mixing board or dedicated preamp (such as PRE).
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003 Rack+ has eight inputs with preamps, to which you can connect low-level signals.
003, 003 Rack, Digi 002, and Digi 002 Rack have four inputs with preamps, to which you can connect low-level signals, and four additional line-level inputs with switchable gain.
Eleven Rack has one Mic input with a preamp and 1 instrument-level Guitar input with a special variable-impedance circuit called True-Z (for more information, see the Eleven Rack User Guide.)
Mbox (3rd generation), Mbox 2, Mbox Pro, Mbox 2 Pro, Mbox Mini, and Mbox 2 Mini each have two inputs with preamps, to which you can connect low-level signals.
For input information for qualified M-Audio devices, see your M-Audio documentation.
For all systems, volume and pan controls for tracks in Pro Tools only affect monitoring levels—not the recording input gain. The LED meters on Pro Tools audio interfaces indicate both full-code (highest level before clipping) and true clipping of Pro Tools output signals. The on-screen meters in Pro Tools indicate only true clipping.
Clipping occurs when you feed a signal to a recorder or mixer that is louder or “hotter” than the device allows. On many analog tape decks, a little clipping adds a perceived warmth to the sound due to tape compression. In digital recording, however, clipping causes digital distortion, which is undesirable and should always be avoided.
When you feed a signal into any audio recording system, including Pro Tools, make sure to adjust the input level to optimize the dynamic range and signal-to-noise ratio of the recorded file. If the input level is too low, you will not take full advantage of the dynamic range of your Pro Tools system. If the input level is too high, the waveform can clip and distort the recording. Set the input levels high, but not high enough to clip.
As a general rule of thumb, try to set levels so that they peak within –6 dB to –12 dB on the input meter without triggering the clipping indicator on your audio interface. Depending on the type of material you are recording and its dynamic range and peak content, you may want to record with higher or lower levels.
You can display a track’s input levels in its Volume/Peak/Delay indicator. Normally, this indicator is set to be a Volume indicator. When you change it into a Peak indicator, it can function as a headroom indicator based on the last peak playback level.
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Control-click (Windows) or Command-click (Mac) a track’s Volume indicator to step through the different indicator modes (Volume, Peak, and Channel Delay) until the indicator displays peak (pk) level.
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(Pro Tools HD Only)
You can use the Calibration mode in Pro Tools to adjust the input and output levels for your audio interface so they match those of your mixing console and other audio devices in your studio.
HD I/O has one set of adjustable trim pots for its inputs. Additionally, the reference level for the input can be set to +4 dBu or –10 dBV. For more information on calibrating HD I/O, see the HD I/O Guide.
192 I/O has two sets of adjustable trim pots for its inputs, and two sets of adjustable trim pots for its outputs. Additionally, the reference level for the input can be set to +4 dBu or –10 dBV. For more information on calibrating 192 I/O, see the 192 I/O Guide.
There are no input or output trims on the following audio interfaces: HD OMNI, HD MADI, 192 Digital I/O, 96 I/O, and 96i I/O. Some Pro Tools audio interfaces that do not have output trims (such as the 96i I/O) offer software-controllable input levels, adjustable from Setup > Hardware (see the guide for your particular audio interface).