Specifications

Chapter 30: Surround Concepts 503
LFE
When a decimal such as “.1” is present in the
name of a surround format, it indicates the pres-
ence of an LFE channel. The LFE channel (for
Low Frequency Effects, also known as Low Fre-
quency Enhancement) refers most often to a
specific track used in production (not during
playback or decoding). LFE is the “.1” compo-
nent in mix formats such as 5.1 and 7.1.
The reason the LFE component is referred to as
“.1” is that unlike the other five or seven speak-
ers, LFE is not full bandwidth (or full-range).
The LFE signal provides a discrete path for low
end to the subwoofer, unaffected by bass man-
agement (if any). Low frequency effects include
such things as thunder, explosions, and other
bass effects.
LFE is generally used to enhance sound effects in
films. There are no set rules about whether or
not you must employ an LFE channel.
Sub Content
When surround mixes are played back on sys-
tems that include one or more subs, subwoofer
content comes from either or both of the follow-
ing sources:
• All bass from all channels that is below the
threshold of the bass management filter cut-
off (if any)
– and –
• Audio in the LFE channel (if any)
A surround sub will play back all the lowest-fre-
quency sounds from all of the other speaker
channels, below a fixed frequency threshold.
The threshold varies among different surround
formats. See “Where to Get More Information
on Surround Technology” on page 504 for a list
of surround specification resources
.
In addition to the frequency cutoffs and other
specifications of each surround format, play-
back system variables can affect sub content. See
“Surround Playback System Variables” on
page 505 for more information.
Divergence
Divergence is a surround mixing control that
lets you set panning “width.” Full divergence re-
sults in discrete (or narrow) panning. Lower di-
vergence settings result in progressively less dis-
crete (or wider) panning.
With Full (100%) divergence, tracks can be
panned exclusively, or discretely, to a single
speaker. Sounds panned to a single speaker are
only audible in that speaker.
When divergence is less than 100%, tracks will
be audible in neighboring speakers even when
panned directly to a single speaker in the grid.
Lower divergence settings result in a progres-
sively wider source signal.
Divergence Example
To understand divergence, it can be helpful to
imagine the inside of a large movie theater. This
is a good example because one of the most chal-
lenging playback variables one faces in multi-
channel mixing is the size of the intended lis-
tening environment.
Pro Tools applies no filtering to LFE sig-
nals. Some delivery requirements may re-
quire filtering for the LFE track. See “Mixing
Formats and Surround Formats” on
page 497 for more information.