Behringer DSP1200P User Manual download pdf (Page 31)

aid of a volume fader, which manually levels the material. During low passages the gain is increased, during

loud passages the gain is reduced. Of course it is fairly obvious that this kind of manual control is rather

restrictive; it is difficult to detect signal peaks and it is almost impossible to level them out. Manual control is

simply not fast enough to be satisfactory.

Fig. 4.4: The interactive relationship between the operating level and the headroom

The need therefore arises for a fast acting automatic gain control system which will constantly monitor the

signals and which will always adjust the gain to maximize the signal-to-noise ratio without incurring signal

distortion. This device is called a compressor or limiter. This system is a part of the BEHRINGER

MODULIZERPRO.

4.3.3 Compressors/limiters

With broadcasting and recording, signal peaks can easily lead to distortion due to the high dynamic range of

microphones and other musical equipment. Compressors and limiters reduce the dynamics by means of an

automatic gain control. This reduces the amplitude of loud passages and therefore, restricts the dynamics to

a desired range. This application is particularly useful with microphones, to compensate for level changes.

Although compressors and limiters perform similar tasks, one essential point makes them different: limiters

abruptly limit the signal above a certain level, while compressors control the signal gently over a wider range.

Both continuously monitor the signal and intervene as soon as the level exceeds a user-adjustable threshold.

Any signal exceeding this threshold will be immediately reduced in level.

Limiters reduce the output level to the adjusted threshold whenever the input signal exceeds this point. With

compression, in contrast to the action of a limiter, the signal is reduced in gain relative to the amount the signal

exceeds the threshold. The output of a compressor will still rise if the input level is increased, while the

maximum output of a limiter will always be equal to the threshold level.

Generally, threshold levels for compressors are set below the normal operating level to allow for the upper

dynamics to be musically compressed. For limiters, the threshold point is set above the normal operating level

so that it only intervenes to protect subsequent equipment from signal overload.

The speed, or rather time settings used can differ greatly depending on use. Although both limiter and com-

pressor use very short attack times, the release time of a compressor are in the 100 ms region whereas a

limiter uses release times of seconds. To be exact: The release time is a time constant of an exponential

function. It is the time it takes the gain reduction to decrease by 63.2% (= 8.7dB).

Because fast level changes are more noticeable than slow changes, long release time are used where unobtru-

sive signal processing is required. In some cases however, the principal goal is to protect devices as loud-

speakers and power amplifiers. In those cases a short release time is more appropriate to ensure that the

limiter only intervenes when it is needed and the level returns to normal as soon as possible.

Long release times are better suited when the limiter should remain inaudible for instance with broadcasting

or club applications or when a signal is transferred to (analog) tape. Please note that when using slow release

4. TECHNICAL BACKGROUND

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Behringer DSP1200P User Manual Page 31