Behringer MDX2200 - Manual (Page 24)

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COMPOSER PRO MDX2200
6. EXTERNAL SIDE CHAIN APPLICATIONS
6.1 The side chain function
The BEHRINGER COMPOSER PRO offers an exceptionally usable external facility by using the side chain
function. By activating the SC EXT switch, the COMPOSER PRO’s control path is disconnected from the
audio input and therefore interrupted. The audio input is routed to the SC SEND output and the SC RETURN
input now receives the new control signal which is derived from an inserted effects processor.
Please note the correct wiring for mains powered units in order to avoid ground loops, as the side chain inputs
and outputs are unbalanced. The working level of external units must be at line level (-20 to +10 dBu) and must
be at unity gain.
6.2 Using an equalizer in the side chain path
It is very common to make the response threshold of a compressor frequency-dependent, where a graphic or
parametric equalizer is connected to the side chain path. To retain the threshold setting of the COMPOSER
PRO, unwanted frequencies should be reduced by an equalizer and the desired frequencies should be kept at
the same level. Should for example, the compressor be controlled by a narrow mid-frequency band, it is
advisable to lower the bass and treble controls. The middle frequency control remains at unity gain.
6.2.1 The COMPOSER PRO as a “de-esser”
“De-essing” is a special application of frequency selective compression. A problem often encountered in re-
cording, is the sibilant (Ssss) sound of the human voice. High frequency, sibilant sounds and pops can pro-
duce very high energy levels which can sometimes cause an otherwise normal and undistorted voice to sound
very harsh, shrill and sometimes unintelligible. The solution is frequency conscious compression or limiting.
The unit responds only to selected frequencies and reduces the level temporarily, as soon assibilant sounds or
pops are detected.
If the detector circuit registers an excessive amount of high frequency information within the program material,
as in a normal compressor, the VCA is activated and the overall level is reduced. As this type of compression
affects the whole frequency range, this process is called broadband de-essing.
Please note that this type of frequency selective compression is very different from simple, fixed equalisation
using notch filters, since de-essing has no effect on the signal except at the instant the sibilant occurs. The
general frequency response is principally not affected during this process.
When de-essing, simply insert an equalizer not into the audio path but into the side chain path of the BEHRINGER
COMPOSER PRO. The equalizer is inserted between the SC SEND output and the SC RETURN input of the
BEHRINGER COMPOSER PRO. While the SC EXT switch is depressed, the equalizer is inserted into the
side chain loop and controls the unit. With the help of the side chain monitor function, the centre frequencies
of the equalizer are then adjusted exactly to match the frequencies of the sibilant sounds. All other frequencies
are filtered out, so that with maximum attenuation of these frequency bands, along with a correctly adjusted
threshold point, the unit responds solely to the selected signal being produced by the equalizer. The level of the
sibilant sounds can therefore be effectively limited.
1. Turn the THRESHOLD control anticlockwise until the GAIN REDUCTION meter shows an appropriate drop
in level.
2. Now press the SC MON switch and adjust the equalizer corner frequencies (generally 6 - 10 kHz) by
monitoring, until it is within the range of the sibilance.
3. Release the SC MON switch and recalibrate the THRESHOLD control, so that the unit reacts only when the
sibilant sound occurs.
Level compensation using the OUTPUT control is not necessary. Although the recommended attack and
release times for this function are proven, the time parameters can be adjusted if necessary to achieve maxi-
mum results. The AUTO function should not be used.
6. EXTERNAL SIDE CHAIN APPLICATIONS