11
Norsonic Nor848
Instruction Manual
Virtual microphone
It is possible to listen in real time to the sound approaching
the acoustic camera from various directions. This is done by
moving a blue circular cursor called a virtual microphone
to the position where you want to listen. The direction is
selected by a left-click in the picture or the circle may be
selected and dragged around. See figure below. Remember
to set the temperature and the focal distance as this may
affect the indicated direction.
Adjacent to the virtual microphone cursor is an indication
of the sound pressure level. Two levels are indicated: the
level as observed by the virtual microphone marked “Beam”
and the sound in any direction reaching the microphone
dish marked “Omni”. The last value correspond to the level
observed with a sound level meter in the position of the
microphone dish. Both levels are frequency-weighted as
selected by the frequency analysis: A-weighted, C-weighted
or un-weighted (No weight).
Frequency band
You can either listen to the full frequency range (20 Hz – 20
kHz) or choose the frequency range selected for the level
colouring. This is done using the selection box marked in
the figure above.
Volume adjustment
Volume is adjusted by moving the volume slider. This is
a software type gain adjustment (computational) and the
level of the resulting signal is shown. Set the volume so the
level is always green, red colour indicates a clipping of the
signal and will reduce the sound quality.
Indication of sound pressure level,
filtered and frequency-weighted
The sensitivities of the microphones are calibrated to dis-
play the sound pressure level referred to 20 µPa at the
position of the microphones, i.e. at the microphone dish.
This is similar to placing a calibrated sound level meter at
the position of the microphone dish.
The frequency range for measurement is selected by the
“frequency mode” function, either as a narrow frequency
band or determined by the selector for the upper and lower
band edge frequency.
Virtual microphone
Band-filtered or
broadband listening
Listening vol-
ume
Volume indication
Time resolution
The value adjacent to the virtual microphone as well as the
level colouring apply a time smoothing called time resolu-
tion. One of the following alternatives may be selected:
• Impulse: 0,035 second averaging time
• Fast: 0,125 second averaging time
• Slow: 1,0 second averaging time
• Sum
Σ:
The
average of a marked time period
(Stored record only)
Note that “Impulse” is a short time constant only and don’t
correspond to Impulse-time function in a sound level me-
ter.
The menu for selecting the time resolution is shown below.
