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Adjusting Spectrum Analysis settings
From the Spectrum Analysis toolbar, click the Settings button ( ) to display the Spectrum Settings dialog. The following table explains
the role of each control in audio spectrum analysis.
Item
FFT size
FFT overlap
Smoothing window
Slices displayed
Description
Choose a value from the FFT size drop-down list to set the size in samples of the
analysis window and number of discrete frequencies analyzed. Higher numbers
produce increased frequency resolution at the expense of lower time resolution and
longer computational time.
The value in the FFT overlap box specifies the percentage of overlap between FFT
analysis windows. Overlapping allows for more accurate analysis. Lower settings
decrease the number of distinct analysis functions performed, which decreases
processing time. High settings allow for more analysis, but can result in slow
processing.
Choose a setting from the Smoothing window drop-down list to determine the
window function applied to the input data before analysis. The window function
affects the sharpness of peaks in an FFT graph and the leakage into neighboring
frequencies.
•Choose Rectangle to apply no window. This results in a very sharp peak, but high
leakage.
•Choose Triangular (also called a Bartlett or Parzen window) to apply a window that
results in less leakage than the rectangle window.
• Hamming, Hanning, and Blackman windows are commonly used in audio
applications.
•Choose Blackman-Harris to obtain the least sideband leakage of the six options.
The major drawback of Blackman-Harris is rounded graph peaks.
The Slices displayed value determines the number of FFT slices displayed. When
displaying multiple slices in the spectrum graph, slices are displayed chronologically
forward or backward based on whether you have the Forward or Backward radio
button selected.
Set sonogram resolution The Set sonogram resolution value determines the number of FFT samplings used in
a sonogram. This keeps the processing time and graph resolution constant. Increasing
this value increases the horizontal graph resolution, but requires more processing
time.
When this check box is cleared, the number of samplings is determined by the length
of the selection and the FFT overlap setting.
Note:
Increasing the samplings increases the horizontal graph resolution but
requires more processing time.
Channel Choose a setting from the drop-down list to specify which graph you want to edit.
USING SPECTRUM ANALYSIS |
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