6
Mackie Industrial White Paper
Noise Sensing
September 2000
2.1 Ambient Microphone
Mackie Designs recommends the Mackie Industrial
MT3100® omnidirectional Electret microphone. This is an
excellent multi-standard phantom condenser microphone per-
fectly suited for noise sensing applications. However, for
many applications, any inexpensive low-impedance, omnidi-
rectional microphone will sufce. An installer may nd that
a directional microphone is better suited for installations in
smaller or noisier rooms. The microphone should be placed
where it can “hear” the ambient noise within the room. This
does not imply that the SP-DSP1™ can not differentiate
between the noise and the program material. However, to
get the best possible performance and rejection, the ambient
microphone should be placed where it is listening to the
“intended” ambient noise source. Any mechanical feedback
(direct vibrations) from speaker to microphone should be
avoided as well as placing the microphone away from the
speakers to provide the best noise-to-signal ratio.
3 Palm™ Control
Mackie Designs has designed the SP-DSP1™ to run under the
Palm™ OS or any compatible palmtop device. The SP-Con-
trol™ Palm™ application (on 3 1/2 inch disk) is included with
the SP-DSP1™ hardware card and can be downloaded from
our WEB site at
www.mackieindustrial.com
. All necessary
cabling is provided to install the card into the SP2400/1200.
Additionally, a 3-inch null-modem adapter cable is provided
to connect a standard Palm™ Cradle or the HotSync® Cable
to the 9-pin female D-Sub on the front of the SP2400/1200.
After installing the application to your device, to run the SP-
Control™ software, simply select the “SP-Control” from the
available applications. You should see the main SP-Control™
window (see Figure 2). The main display has six user parame-
ters and four bar graphs indicating the relevant levels. Because
of limited screen space, we used two-letter symbols designat-
ing the parameters and levels. Table 1 summarizes the six
parameter ranges and their default settings after a
Factory
Restore
.
3.1 User Parameters (Sliders)
As the parameter
Minimum Gain
implies, this is the lowest
level to which the system can attenuate. With this slider
default at –40dB, the system can attenuate the program input
by as much as 40dB. Please note that the SP-DSP1™ can
only attenuate program material that is present on the input.
That is, this system (see Figure 0) will never allow gain from
input to output (
≤
0dB). By setting the
Minimum Gain
and the
second parameter,
Gain Range
, you are actually establishing
the program operating window within which the levels for
the program material must remain. For example, if the user
wanted his music levels to operate in a range
±
10dB around
-15dB down from the input level, he would set
MG
=-25dB
and
GR
=20.
“
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
Table 1: SP-Control™ User Parameter Ranges and Defaults
Figure 2 SP-Control™ Main Screen
