DigiDesign Pro Tools Reference Manual page 660

Mastering and Audio Compression
Although audio compression is often an indis-
pensable tool in analog recording, it can present
problems in the digital domain. If you compress
an input signal at a very high ratio, you create a
signal that contains a much higher overall
power level compared to its transients. By re-
cording a number of such signals at the highest
possible level on multiple tracks, you create a
scenario that is more likely to clip the mixed
output signal.
High-power compressed signals, when mixed
together, create an extremely high-level output.
This output may rise above the full-code level,
resulting in clipping.
To avoid this problem, watch the overall level of
your program material—use a meter on a Master
Fader, or use an external mastering deck's
meters to help identify clipping. If you are mas-
tering to hard disk, avoid mixing full-code audio
signals together at unity or "0" level, as this in-
variably causes clipping.
Mastering and Error-Correcting Media
Random access media (such as hard disks, opti-
cal cartridges, Bernoulli cartridges or WORM
drives) can produce a true digital copy of your
data, because every bit value is maintained. Se-
quential media (such as DAT tapes) use error
correction schemes to fix the occasional bad
data that is received in a digital transfer. These
corrections are deviations from the actual data,
and with successive reproductions, represent a
subtle form of generation loss.
You can avoid this loss by creating and main-
taining masters on random-access digital media
(such as a hard drive) and transferring them to
sequential digital media (such as DAT tapes)
only as needed.
648 Pro Tools Reference Guide
To configure Pro Tools for direct digital stereo
mastering:
Connect your digital recorder to your system's
1
digital outputs. If your system has multiple dig-
ital outputs, use channel 1 and 2 of the audio in-
terface.
In Pro Tools, set the appropriate digital format
2
and output from the Hardware Setup dialog or
I/O Setup dialog. (See "Configuring Pro Tools
Hardware Settings" on page 46.)
Set the clock on the master device to slave to
3
Pro Tools digital clock, or to provide master
clock to Pro Tools. (See "Configuring Pro Tools
Hardware Settings" on page 46.)
On your digital recorder, choose the appropri-
4
ate digital format for the connections.
In Pro Tools, set all audio tracks you want to
5
your master outputs 1–2 path.
Click Return to Zero in the Transport window
6
to go to the beginning of the session.
Press Record on your digital recorder.
7
Start playback of your session.
8
When your session has finished playing, stop
9
the digital recorder.