Raising a Signal Out of a Mix
Since reducing dynamic range increases the average signal level by a small amount, a single
track can be raised out of a mix by boosting its level slightly and applying compression. Start
with a 2:1 RATIO and a relatively low THRESHOLD setting (-20dBu). Adjust both controls as
necessary.
Compressors have also been used to bring vocals to the forefront of a mix in volume-restricted
studios (e.g. home studios). Start by adding a foam windscreen to the mic (if it doesn’t have
one). Set the RATIO to 10:1 and the THRESHOLD to -10dBu. With your mouth approximately 2
inches from the mic, sing the vocal part, but with less volume than normal. Use phrasing to
give the part some intensity. An equalizer (e.g., a dbx 2 Series, 12 Series or 20 Series Graphic
Equalizer) or a vocal effects device (e.g., reverb, delay, distortion) can be added to further
define the performance.
It is also possible to separate certain vocals or instruments from a mono program already
mixed: refer to frequency-weighted compression on page 18.
NOTE:
When compressing a stereo program with a 166xs, the factors affecting a
compression curve and the actual RATIO and THRESHOLD settings, are like those previously
covered with reference to single channels of program material. However, it will generally
be found that large amounts of compression are more audible in a mixed stereo program
than they might be on the separate tracks that were mixed to create the program.
Preventing Analog Tape Saturation
With programs of widely varying levels, compression can prevent recording levels (e.g., cymbal
tracks in a final mix or drum kit submix) from saturating tape tracks (see frequency-weighted
compression, on page 18).
Preventing Digital Overload
Digital recorders and samplers produce audible distortion when they exceed their headroom
(i.e., the range above their maximum operating level). The 166xs effectively ensures that
audio input does not overload a digital recorder’s A/D (analog-to-digital) converters. The
166xs can perform this function quietly enough for all digital media. To use the 166xs
so that no changes in gain occur unless an emergency arises (wildly excessive levels), set
Hard Knee mode On, the RATIO to
∞
:1, and the THRESHOLD to the highest permissible level.
NOTE:
PeakStop limiting can also be used to prevent raucous-sounding digital overload.
Speaker Protection (Auditoriums, Churches, Mobile DJs and Sound Systems)
Digital recorders and samplers produce audible distortion when they exceed their headroom.
Compressors are frequently used to prevent excessive program levels from distorting power
amps and/or damaging drivers in a sound-reinforcement system (whether you’re doing
auditorium, church, or club sound engineering, or are a mobile DJ, or like to push the limits
of your home’s audio entertainment center). Set the 166xs for limiting (Hard Knee mode
On, with a RATIO of 10:1 or greater) and adjust the THRESHOLD to provide 15dB or more
of compression (just a few dB below the input clip). For low-level signals, the 166xs won’t
change gain, but if large signals come along, the gain will be reduced to prevent clipping and
save sensitive system components from excessive heat buildup or other type of damage.
Section 4
Operating Notes
17
dbx 166xs
