7
Mackie Industrial White Paper
Noise Sensing
September 2000
The second parameter,
Gain Range
, also sets the maximum
gain attainable from the
Minimum Gain
. That is:
Prog. Operating Window = Min. Gain + Gain Range = Max. Gain
(3)
The
Gain Range
slider “re-scales” so that system gain (input
to output) is never greater than 0dB. So, if
MG
=-10dB, then
GR
≤
10dB. In most cases, the user can ignore the
Gain Range
parameter. He would simply set the desired
Minimum Gain
of
the music (either by listening or from calculation) and leave
the
Gain Range
at the default “re-scaled” setting.
The third parameter,
Noise Threshold
, sets the noise “trigger”
of the algorithm. Until the noise level exceeds this threshold,
the throughput program level is unaffected. This slider actu-
ally sets the “noise” sensitivity of the algorithm.
NT
is relative
to the unity point which is –10dBFs (from full scale). There-
fore, if
NT
=-80dB, this would indicate a noise threshold level
of –90dBFs (where Fs = 1V RMS). In simplistic terms, the
lower the
Noise Threshold
(more negative), the more sensitive
program level changes are to noise level variations. The
Noise
Threshold
parameter in conjunction with the fourth param-
eter,
Noise Range
, actually sets the operating window of the
noise source. This noise “window” sets the level and range
that the noise must be within to effect the program level:
Noise Window = Noise Thr Noise Range
(4)
The
Noise Range
setting gives the user control over how much
noise level change causes the program level to span it’s
Gain
Range
. By setting a small
Noise Range
(say 20dB) with regard
to the
Gain Range
(say 30dB), you are allowing a 20dB noise
level change to cause the program output level to span 30dB.
This is assuming that the noise level has crossed the
Noise
Threshold
. In other words, these settings would represent a
2:3 noise level to program level change (see Chart 1). For
every 2dB change in noise level, the output level changes by
3dB. On the other hand,
NR
=40 and
GR
=40 (default settings)
“
MG
”=
“
GR
”=
“
NT
”=
“
NR
”=
Attack/
Min. Gain
Gain Range
Noise
Noise Range
Release
(dB)
(dB)
Threshold
(dB)
(dB)
Time
(sec.)
Minimum:
-40
0
-80
1
1
Maximum:
0
40
0
60
300
Default:
-40
40
-40
40
1
+10dB
+5dB
0dB
-5dB
-10dB
-15dB
-20dB
-25dB
-30dB
-40dB
-35dB
-50dB
-45dB
-55dB
-60dB
-65dB
-70dB
-75dB
-80dB
Default setting
Ratio: 1:1
Note: Ratio=Noise:Program
NT=-80
MG=-30
NR
GR
=Program Operating Window
=Noise Window
Unity:
FS:
GR
NR
NT=-40
MG=-40
Lowest NT, Highest NR
Ratio: 2:1
Sensitive to low noise
GR
NR
NT=-30
MG=-20
GR
NR
NT=-60
MG=-35
Average setting
Ratio: 3:2
Good for small room
Average setting
Ratio: 2:3
More Sens., Larger room
(In=Out)
Good starting point
Chart 1: Noise Window vs. Program Operating Window Examples
