Справочник Пользователя для Mackie VLZ3 4BUS

Owner's Manual   

17

At the maximum compression, the threshold is set at  

0 dBu, and the input to output relationship is  
represented by the lower curve. If the input is -5 dBu 
(that is, below the threshold), the output is -5 dBu. As 
the input reaches 0 dBu, the output is a bit less than  
0 dBu. If the input is +5 dBu, the output is about  
+2 dBu. If the input reaches +10 dBu, then the output 
is +3 dBu. Notice the shapely curve of the soft knee 
between the diagonal slope of x = y  and the compressor 
slope of 6:1 (the compression ratio). 

The other blue curves represent in-between positions 

of the compressor knob, with higher thresholds before 
compression begins.

Outboard compressors often have controls such as 

compression ratio, threshold, soft knee/hard knee,  
attack time, and release time. These last two affect how 
quickly the compressor kicks in when the input exceeds 
the threshold, and how quickly it is released after it 
drops below the threshold. In this compressor, these 
parameters are specially chosen to give you the best 
overall performance.

Adjust the threshold carefully, so your dynamic range 

is still lovely, without distortion or overload during the 
performance. Run through a few practice screams and 
high-notes, and adjust the compression as required.

Each of the last four mono channels in the  

 

VLZ3 4•Bus mixer has an in-line compressor circuit 
with a variable threshold. This is very useful for    
compression of vocals, and snare drums, for example, 
so you might consider connecting your microphones 
and drum mics to these channels, rather than other  
channels.

When the incoming signals exceed the threshold level 

set by this knob, the signal level is automatically  
compressed. This reduces the dynamic range, and 
reduces the chance of distortion due to overloading the 
input signals.

Dynamic range is the difference in level  
between the quietest and loudest parts of a 
song. A compressor "squeezes" the dynamic 
range, resulting in an overall steadier, more 

constant volume level for the signal. It helps sources, 
such as vocals, "sit" properly in the mix; it is very useful 
for live sound.

The compression ratio is fixed at around 6:1, with 

a soft knee response. The threshold can be adjusted 
clockwise from off (no compression) to 0 dBu (max).

As an example, suppose the threshold is set to  

maximum. An incoming signal reaches the threshold of 
0 dBu. As it increases beyond the threshold, it becomes 
compressed at a ratio of 6:1. This means that even if the 
input further increases by 6 dB, the actual output only 
increases by 1 dB. This compresses the output signal, so 
there is more protection to your system from distortion 
and overload due to poor microphone technique (say 
it ain't so) and general pops, bangs and heavy metal 
screaming. The soft knee means that the compression 
slowly ramps up to 6:1 from the threshold. It does not 
jump abruptly to 6:1, as this would be hard knee  
compression, and harder on the ears too.

The graph on this page shows the input signal level 

going into the compressor, versus the output level    
coming out of it. It is the typical graph to see when   
compressors are discussed, and is just the kind of thing 
our engineers like to discuss during the company  
Christmas party*.

If the compressor is off, then the input = output. For 

example an input signal level of +5 dBu results in an 
output level of +5 dBu. The diagonal line from lower left 
to upper right represents x = y, that is, input = output.

* My High School math teacher, Mr. Marvin, thought that 
graphs might come in handy for me one day. Finally!