Larson Davis SoundAdvisor 831C Reference Manual page 145

SoundAdvisor Model 831C
Step 4.
On the General tab, the Default Data File name you enter here is a prefix for
each data file generated using this Setup.
Step 5.
To create an ISO compliant measurement, use the Measurement Description
field to enter a thorough description of the measurement site, mic location,
source location, etc., (See ISO 1996-2, section 12). This can also be easily
managed in G4 after the measurement is downloaded.
Step 6.
Press the right softkey (
Step 7.
On the FFT tab, choose a Frequency Span, which specifies the upper end of the
frequency spectrum that should be sampled.
Step 8.
From the Lines drop-down menu, choose the number of Lines of sampled data
to be collected for each frequency.
Your selection for Frequency Span and Lines results in the Frequency
Resolution. This is done by dividing your selection for frequency span by the
number of Lines, sometimes called "bins." The result is the bandwidth of each
line (bin) in Hz/line or bin. Also, note that selecting a greater number of lines
increases the FFT computation time.
For your selected frequency resolution, the SoundAdvisor 831C
TAKE NOTE
calculates the FFT measurement accurately to within 0.1 dB.
Sampled Data and the Windowing Function
With fast Fourier transform mode,
when the measured signal doesn't use
up an even number of lines or when
the number of lines is not a multiple of
the sampling frequency, the resulting
data "smears" into the adjacent lines.
This results in
frequency values that were not part of
the original signal.
Step 9.
Choose a Window method from the drop-down menu. The following options
are available:
Rectangular: The windowing method distinguishes frequencies that are close
together in the examined spectrum, but compromises on amplitude details.
Use this method to view sounds within a particular spectrum.
//*
) to set preferences on the FFT tab.
additional high-
Creating an FFT Setup File On the Meter
The Windowing function helps to
account for this smeared
(Spectral Leakage) leading to a more
accurate representation
measured sound. It does this by
zeroing the time domain function at
the beginning and end of each record
and by representing the wave form in
an alternative sine wave format. See
the following figures for more detail.
data
of the
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