Behringer XR4400 manual Proper positioning of microphones, Applications

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 19