DADiSP Software
Modules - DADiSP/Octave
 1/N Octave Analysis Module
Octave analysis displays the frequency characteristics of a signal by
passing the signal through a bank of bandpass filters. The center frequency
of each filter is twice the center frequency of the previous filter.
Each filter covers a bandwidth that is twice as wide as the previous
band and half as wide as the next band. One octave corresponds to a doubling
of frequency.
Proportional Bandwidth Octave Filters
Unlike standard FFT spectrum analysis, octave filters exhibit proportional
bandwidth. If the lower and upper cutoff frequencies of a bandpasss filter
are fl and fh, then the center frequency, fc, can be determined with:
This proportional bandwidth property divides frequency information over
a log scale and is very useful in analyzing a variety of natural systems.
For example, the human response to noise and vibration is very non-linear
and many mechanical systems have a behavior that is best characterized
by proportional bandwidth analysis.
Fractional Octaves
For greater resolution, the frequency range can be divided into proportional
bandwidths that are a fraction of an octave. For example, with 1/3 octave
analysis, there are 3 bandpass filters per octave where each center frequency
is 21/3 the previous center 1/3 and 1/6 Octave Analysis frequency and
In general, for 1/N octave analysis, there are N bandpass filters per
octave such that:
where 1/N is called the fractional bandwidth designator.
Digital Bandpass Filter Method
DADiSP/Octave provides 1/N octave analysis using true IIR digital filters
that conform to ANSI S1.11 and IEC 1260 specifications. Each band filter
is designed in accordance to ANSI S1.11 and IEC 1260 specifications by
transforming the original analog transfer function to the digital domain
by means of the bilinear transform. The filter order can be specified
and the frequency ratio can be calculated using the binary or decimal
system.
 Standard or Custom Center Frequencies
Center frequencies can be specified as a range of ISO band numbers for
standardized octave analysis. User defined center frequencies as a range
or list of values are supported to facilitate custom applications.
Input and Output Options
A, B, and C weighting filters can be applied to the input data. Output
results include mean power, max power, min power and un-weighted RMS
values. The output can be normalized with a calibration value. The results
can be plotted on log or linear axes and exact or preferred frequency
values are supported. The output can be displayed in a variety of plot
styles including bar, step and line plots.
Requirements
DADiSP/Octave requires DADiSP 6.0 B17 or higher. Contact us for information
about updating your current version of DADiSP. | 
