Klark Teknik DN540 Manual Do Utilizador

21

The compression threshold is the point at which the compressor begins to operate.  
Signals that exceed this point, that is, go over threshold, will be affected by compressor 
actions.  However, signals below the threshold do not trigger any compression, but may 
still be affected by compression releases from previous over threshold signals.

If the compressor is being used as a limiter, the threshold level is the level at which the 
limiter begins to operate.

The presence function protects the mid-high frequencies during compression.  It does 
this progressively, so that the compressor appears to operate with two different ratios, 
one for low frequencies (normal) and the other for mid-high frequencies (reduced 
ratio).  The primary effects of this are:

• Heavy compression and dynamic control can be applied without the programme 

sounding unnatural.  Reduced compression in the presence band where the ear is 
most sensitive (and where there is comparatively little acoustic energy) masks the 
dynamic control that is applied to the high energy high and low frequency signals.

• The compressed material sounds brighter.  However, because no high frequency gain 

is added when compression is not required, noise during quiet passages is reduced 
and the tendency for high frequency howl-round (which can often be a problem if air 
brightness is added by conventional EQ post compression) is also reduced.

• Side effects of this approach are that the high frequency content of spill remains 

more consistent, and pumping is therefore much less noticeable.

Some DN540 frequency response curves are shown in Figure 4, “Presence frequency 
response curves,” on page 21, which help to illustrate the effect of the presence 
function.  The curves were produced with the compressor at -50dB attenuation, and 
with the PRESENCE control knob set to MIN, MAX and an intermediate value.  Note 
how the MIN setting produces the flat line towards the bottom of the graph.  At this 
setting all audio frequencies are attenuated by the same amount as set by the 
threshold, ratio and input signal level, which effectively defeats the presence feature 
completely.  As PRESENCE is turned clockwise the protective filter is activated.  At the 
MAX setting, which is -3dB at 5kHz, the frequencies around 5kHz are hardly reduced in 
level at all, whereas the lower frequencies and very high frequencies are still 
compressed significantly.

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