Acoustic Research Ngara, User Manual

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Ngara
User Manual
3.1.3.3.2 PCM Data
Ngara is capable of storing raw audio samples. The raw files can be used in conjunction with FireFly to obtain octave
spectrum analysis of the data. More information on FireFly can be found
here .
PCM samples are stored as single channel data and are taken directly from the microphone output voltage. These
samples are used internally during SPL calculations and are sampled by the Analog-to-Digital-Converter (ADC) at a
constant rate of
48 kHz
.
Ngara uses internal range switching to obtain a greater dynamic range. This is reflected within the Signal
Condition
field within the CSV file entry, with the switching occurring every
100 ms
as required. If the signal
is in the high range (value of
2
) the data needs to be multiplied by the logger’s saved multiplication factor.
Allowable raw audio configurations are shown in Table 5.
Table 5: PCM Configuration Options
Option
F
s
bit-depth Auto-ranged
OFF
48kHz
48 kHz
16-bit Yes
12kHz
12 kHz
16-bit Yes
12k/8
12 kHz
8-bit No
NCam
48 kHz
16-bit No

PCM data must be recorded at 48kHz if post processing is to include octave analysis of the data
Continuous
Continuously recorded Pulse-Coded-Modulation (PCM) data will be stored to the USB storage device if selected by
the user.
Files are rotated every hour on top of the hour, with filenames corresponding to time and date.
Triggered
Triggered Pulse-Coded-Modulation (PCM) data will be stored to the USB storage device if selected by the user.
Files are rotated in the event that a triggered wave files exceeds two hours duration.
3.1.4 Data Usage
Table 6 describes the expected data usage requirements for various logger configurations.
Table 6: Standalone Logger Data Usage
CSV Data PCM Data PCM
F
s
(kHz) PCM bit-depth Usage ( GB )
Y N 0.04
Y Y 48 16 8.00
Y Y 12 16 2.00
Y Y 12 8 1.00

CSV
data is always recorded and cannot be disabled
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