Behringer XR4400 - Manual (Page 19)

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MULTIGATE PRO XR4400
signal will not be suppressed completely. Although the MULTIGATE PRO allows for a maximum gain reduction
of 80 dB, it is usually not useful to reduce the signal level by this maximum amount. In particular, with highly
noise-affected signals we recommend that you use a signal attenuation of not more than 10 to 20 dB, so that
the onset of the gate function will not become too obvious.
6.1.2 The expander function
In contrast to the gate function, the expander triggers a continuous attenuation of the signal, as soon as it has
dropped below the threshold.
RATIO control
With the MODE switch in, the MULTIGATE PRO works as an interactive expander. The RATIO control
determines the expansion curve. For example, when a piece of music was highly compressed during the
recording session, the lost dynamics can be restored through complementary expansion. With a bit of feeling
you can set the following controls by ear so that the original dynamics (prior to the compression process) will
be restored.
We recommend that you set the RATIO control to about 1:1.2 through 1:2 to allow for a “smooth” expansion
curve, and that you adjust the THRESHOLD control so that the entire dynamic range of the music piece will be
below the threshold point. Now set the THRESHOLD control so that only the loudest passages of the program
material surpass the threshold point (“-” LED flashes). In the same way, you can artificially expand the dy-
namic range of any instrument. In particular, when processing sampled sounds, expansion can produce nice
results, because samplers usually have a highly limited dynamic range. When processing percussion sounds
(e.g. snare drum) you can use downward expansion to create interesting effects, for example, by setting the
threshold to about mid-position, so that only the “lower” part of the dynamics will be processed: the signal
decays unchanged until the adjusted threshold is reached, and any subsequent signal portions are faded out
with increasing attenuation.
6.2 Proper positioning of microphones
The main task of an expander is to separate unwanted background noise from the actual signal and to
eliminate this noise “inaudibly”. Understandably, there must be a minimum difference in the levels of wanted
signal and interference signal, so as to be able to define a threshold point for the expander.
However, the optimum operation of an expander depends on the proper choice and positioning of the
microphones:
Be extremely careful when instruments with high-frequency portions are played to the sides or back of a
microphone with a cardioid polar pattern. Most room microphones suffer from a deterioration of their directivity
when picking up high frequencies. For example, with a sensitivity difference of not more than 2-3 dB around
5-10 kHz between the main and lateral axes, cymbals can produce enormous crosstalk in tom-tom
microphones, or the hi-hats can mask the sound of the snare drum.
You should make optimum use of the specific directivity of a microphone to acoustically separate other
instruments as perfectly as possible. Do as best as you can to separate the sound sources acoustically
simply by positioning the microphones correctly.
Yet, in some applications even perfectly positioned microphones might not produce satisfying results. With its
side-chain function the BEHRINGER MULTIGATE PRO gives you the option of frequency-selective expansion
and thus another aid to ensure perfect acoustic separation of the sound sources.
6.3 Applications
6.3.1 Suppressing crosstalk in multi-track applications
One of the most frequent applications of an expander/gate is the elimination of unwanted crosstalk between
single channels during recording or playback. In particular, when recording acoustic drum sounds, this type of
application is frequently used, because here several microphones closely positioned next to each other are
used.
6. APPLICATIONS