Manual-
Dynamic EQ
Dynamic EQ
differs from the forms of compression listed above
in that it dynamically controls the boost/cut of a parametric
filter rather than broadband frequency gain. The basic dynamic
EQ uses a bandpass filter in the side-chain with variable center
frequency and bandwidth. The side-chain detector is sensitive
only to the passband frequencies. A parametric filter with match-
ing bandwidth and center frequency is placed in the main signal
path and the boost/cut of the filter is controlled the same way a
broadband compressor boosts or cuts broadband gain.
Relative Threshold Dynamic EQ
Relative Threshold Dynamic EQ
is a special form of dynamic
EQ where the rms level of the bandpass signal in the side-chain
is compared to the rms level of the broadband signal. The
differ-
ence
between the bandpass and broadband levels is compared to
the threshold rather than the absolute rms value of the bandpass
signal. The advantage of this type of dynamic EQ is that the
relative
amplitude of a band of frequencies, as compared to the
broadband level, is maintained regardless of broadband ampli-
tude. The typical topology is shown in Figure 3.
INPUT
OUTPUT
SIDE-CHAIN
ATTACK
GAIN COMPUTER
FILTER
THRESHOLD
RELEASE
SCALE
RATIO
FREQ BW
BANDPASS
BROADBAND
BANDPASS
RMS
DETECTOR
PARAMETRIC EQ
BROADBAND
RMS
DETECTOR
Figure . Relative threshold dynamic EQ block diagram.
De-essers
De-essing limits or controls the sibilant content of speech.
Sibilance produces a hissing sound. English sibilant speech
sounds are (s), (sh), (z), or (zh). De-essing is often confused as
a type of dynamics processor. It’s actually a specific application
that is accomplished using many different types of dynamics
processors. And contrary to popular belief, successful de-essing
is not as simple as placing a bandpass or treble-boost filter in the
side-chain and calling it done. Frequency Sensitive Compression,
Split-Band Compression, Dynamic EQ and Relative Threshold
Dynamic EQ are all used for de-essing.
True de-essing involves comparing the
relative difference
between the troublesome sibilants and the overall broadband
signal, then setting a threshold based on this difference, there-
fore it is our experience that Relative Threshold Dynamic EQ
(as described above) is the best dynamics processor for this task
as it is able to maintain proper sibilant to non-sibilant balance
regardless of level.
A good de-esser looks at the average level of the broadband
signal (20 Hz to 20 kHz) and compares it to the average level of
a bandpass filter in the side-chain. The threshold setting defines
the
relative
threshold, or
difference
, between broadband and
bandpass levels, which result in compression of sibilants. Because
de-essing depends on the ratio of sibilant to broadband signal
levels, it is not affected by the absolute signal level, allowing the
de-esser to maintain the correct ratio of broadband to sibilant
material regardless of signal level, as shown in Figure 4.
-45
0
-42.5
-40
-37.5
-35
-32.5
-30
-27.5
-25
-22.5
-20
-17.5
-15
-12.5
-10
-7.5
-5
-2.5
20
20k
50
100
200
500
1k
2k
5k
10k
Frequency (Hz)
Increasing Level
De-essing
L
e
v
e
l
d
B
u
Figure 4. The C4’s De-essing performance remains consistent with
varying input levels.
This means that the de-essing performance is consistent and
predictable, regardless of how loud or quiet the singer/talker is.
Taming sibilance when the talker is quiet is just as important as
when the talker is at a fevered pitch.
Figure 5 shows what happens using a primitive de-esser
with a side-chain EQ. Sibilance during loud passages is attenu-
ated, but there is no gain reduction during quiet passages, even
though there may still be a significant amount of “sss” in the
person’s voice. For a given threshold, this often results in an
overly aggressive effect during the loud choruses, and a com-
pletely ineffective result during the hissy, whispered verses.
20
20k
50
100
200
500
1k
2k
5k
10k
-45
0
-42.5
-40
-37.5
-35
-32.5
-30
-27.5
-25
-22.5
-20
-17.5
-15
-12.5
-10
-7.5
-5
-2.5
Frequency (Hz)
L
e
v
e
l
d
B
u
Increasing Level
De-essing
No De-essing
Figure 5. Primitive de-esser with a simple side-chain.
Varying input levels adversely affects de-essing.
