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

Description

FFT size

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.

 

 

FFT overlap

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.

 

 

Smoothing window

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-Harristo obtain the least sideband leakage of the six options.

 

The major drawback of Blackman-Harris is rounded graph peaks.

 

 

Slices displayed

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 287