Behringer MDX1400 manual IRC curve characteristic of the Expander

AUTOCOM PRO MDX1400

Clipping

In contrast to the two previously mentioned limiters, the clipping mode features infinitely fast control times, an infinite compression ratio and creates an unsurpassable barrier (“brickwall”) for all signals above a certain level. To be able to control the signal peaks, the clipping function radically cuts signals above the threshold, without affecting the amplitude of the original signal. If used in normal applications, this function remains inaudible and under certain circumstances it can even lead to an improved sound, because cutting the transients creates artificial harmonics. If misused, clipping can cause very obvious and distasteful distortion, which in an extreme manner, will convert the signal’s waveform into a square wave signal. This effect is often produced in guitar distortion devices (“fuzz boxes”).

3.2 Expander/Gate Section

The main task of the Expander/Gate is to “inaudibly” eliminate undesirable background noise from the usable signal. As additionally described in chapter 6.4, a downward expander automatically reduces the overall level for all signals below an adjustable threshold. The expander therefore operates in opposite way to that of a compressor/limiter. Expanders generally function with a flat ratio curve, so that the signal continually fades. Noise gates however, can be seen as “high ratio” expanders. If the signal falls below the threshold, it is radically attenuated.

The BEHRINGER AUTOCOM PRO is equipped with a newly developed IRC (Interactive Ratio Control) Expander, the ratio of which is automatically adjusted dependent on the program material. The response characteristics of conventional expanders tend to cut into the signal abruptly and the result of this is unacceptable most of the time. Gain changes become audible.

The IRC Expander is therefore equipped with a soft, interactive non-linear ratio curve, which is best suited to human hearing. Critical signals in the vicinity of the threshold level are processed with a minute expansion ratio, whereas signals that reduce in level will be subjected to an increasingly higher ratio, which will result in greater attenuation.

Output

Gain 0 dB

Threshold

IRC-Curve

Expander, 1:8

Noise Gate, 1:oo

Input

Fig. 3.1: IRC curve characteristic of the Expander

The result is expansion, which is less critical to adjust and which is more tolerant of useable signals, whose level is slightly above that of the noise floor. Expansion therefore occurs extremely “soft” with low ratio settings, while the known negative effects of expansion are inaudible. The Attack time of the IRC expander is set automatically and program-dependent, i.e. extremely short for quickly changing signals and slower for a more balanced program material. Since the expander/gate adapts itself automatically to the program material, you will note that the new IRC (Interactive Ratio Control) circuit produces considerably better results than conventional expanders.

3.2.1 Controlling Leakage In The Studio

Expander/gates are most commonly used to suppress undesirable leakage of sound from one track to another during recording or playback. They are usually used when recording drum kits, where the mics are very close to each other. High volume levels of individual instruments often cause considerable leakage onto all the

12 3. APPLICATIONS