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LabVIEW
Advanced Signal Processing
Signal Processing Toolset
Digital Filter Design
Easy-to-use GUI software for
interactively designing IIR and FIR
digital filters
Output filter coefficients for use with
LabVIEW or BridgeVIEW
Super-Resolution Spectral Analysis
Model-based Spectral Analysis
High frequency resolution using a
small data set and modal analysis of
damped sinusoids
VirtualBench-DSA
Easy-to-use, GUI software
for dynamic signal data
acquisition and analysis
Third-Octave Analysis
31-band third-octave analysis
Joint Time-Frequency Analysis
Award-winning Gabor Spectrogram
STFT (sliding-window FFT)
Wavelet and Filter Bank Design
Interactive wavelet design
Output filter and wavelet coefficients
for use with LabVIEW
Overview
The Signal Processing Toolset gives end users ready-to-run stand-
alone signal processing capabilities, and developers high-level
digital signal processing (DSP) tools and utilities. The toolset
includes components for digital filter design, third-octave
analysis, joint time-frequency analysis (JTFA), wavelet and filter
bank design, super-resolution spectral analysis, and the Virtual
Bench-DSA for dynamic signal acquisition, display, and analysis.
The table to the left lists different types of applications and
identifies the components of the Signal Processing Toolset that
can be used in those applications.
Digital Filter Design
The digital filter design component of the Signal Processing
Toolset is a general-purpose design tool for signal conditioning,
control systems, digital signal processing (DSP), and virtual
instrument (VI) applications. It includes a ready-to-run, stand-
alone application for interactively designing digital filters. The
output of the design application is a set of coefficients for use
with LabVIEW.
Applications
JTFA
Wavelet
Digital
Third-
Super-
Virtual
and
Filter
Octave
resolution
Bench-
Filter Bank
Design
Analysis
Spectral
DSA
Design
Analysis
Spectral analysis
Ö
Ö
Ö
Ö
Ö
Ö
Machinery measurements
Ö
Ö
Ö
Total harmonic distortion
Ö
Ö
Frequency response
Ö
Ö
Noise measurements
Ö
Ö
Ö
Ö
Ö
Signal generation
Ö
Using the Digital Filter Design Application
With the Digital Filter Design stand-alone application, you can
quickly and easily design digital filters for signal conditioning and
control systems without being a DSP expert. You can use the
powerful graphical user interface (GUI) and interactively design
classical filters such as lowpass, highpass, bandstop, and
bandpass digital finite impulse response (FIR) and infinite impulse
response (IIR) filters without programming. In addition, the
digital filter design application includes the ability to create
arbitrary response filters by interactively modifying the
magnitude response plot. The digital filter design application also
includes the ability to use National Instruments data acquisition
(DAQ) hardware to filter and analyze real-world signals.
Impulse response
Ö
Biomedical signal analysis
Ö
Ö
Ö
Ö
Network analysis
Ö
Ö
Speech analysis
Ö
Ö
Ö
Ö
Sound power measurement
Ö
Ö
Ö
Ö
Ö
Filter evaluation
Ö
Ö
Ö
Ö
Ö
Filter testing
Ö
Ö
Ö
Ö
Ö
Dynamic signal analysis
Ö
Ö
Ö
Phase measurements
Ö
Ö
Ö
Ö
Transfer function calculation
Ö
Ö
Signal identification
Ö
Ö
Ö
Consumer products testing
Ö
Ö
Data compression
Ö
Image compression
Ö
Table 1. Signal Processing Toolset Application Areas
National Instruments
Phone: (512) 794-0100 • Fax: (512) 683-8411 • info@natinst.com • www.natinst.com
97
LabVIEW
Advanced Signal Processing
Using the Digital Filter Design Utilities
LabVIEW developers also use the filter coefficients created by the
digital filter design application with the built-in FIR and IIR
functions in the LabVIEW Full or Professional Development
System for real-time signal conditioning and control applications.
Third-Octave Analysis
The third-octave analysis component of the Signal Processing
Toolset includes a ready-to-run, PC-based third-octave analyzer, as
well as a set of readily customized software in the form of a
LabVIEW VI library. With the third-octave analysis tools, you can
acquire signals with National Instruments DAQ products as well as
analyze and visualize signals with a third-octave analyzer GUI. You
can use third-octave analysis in diverse applications such as
acoustics, analog telephony, sound pressure measurements,
vibration analysis, noise specification, and audio signal processing.
Digital Filter Design Application Functionality
IIR Algorithms
Elliptic
Inverse Chebyshev
Chebyshev
Butterworth
Using the Third-Octave Analyzer
Use the ready-to-run application to acquire and analyze signals
immediately; no software development is necessary. With the
powerful GUI of the third-octave analyzer, you can set up from one
to four input channels with different windowing, weighting, and
averaging capabilities. You can also store data to file, recall data from
file, and recall previous settings. The third-octave analyzer adheres to
ANSI Standard S1.11-1986. The sampling rate and resolution are
determined by the specifications of the DAQ product.
FIR Algorithms
Parks-McClellan
Minimize FIR filter
Order
Outputs
Magnitude response (dB or linear)
Phase response
Time waveform
Pole-zero plot
H(z) transform
Impulse response
Step response
Polar form
Rectangular form
Filter coefficients for LabVIEW
Third-Octave Analysis Utilities
You can create your own custom third-octave analysis applications
using the LabVIEW Full or Professional Development System and the
LabVIEW Third-Octave Analysis VIs. In addition, there are LabVIEW
third-octave analysis and data acquisition examples to help you
create your own custom applications.
Data Acquisition Specifications
• Sampling rate and update rate dependent on hardware
• Up to 4 channels of analog input
• Broadband dynamic range of 93 dB*
• 92 dB THD for high accuracy*
• Sampling rates of 12.8, 25.6, and 51.2 kS/s*
*All hardware specifications are for the PCI-4451, 4452, 4551 and 4552 dynamic
signal analyzer boards
File I/O
Filter data from file
Save coefficients to file
Data acquisition
One channel of analog input
Single acquisition and continuous modes
98
National Instruments
Phone: (512) 794-0100 • Fax: (512) 683-8411 • info@natinst.com • www.natinst.com
LabVIEW
Advanced Signal Processing
Third-Octave Analysis Functions
Windows
Rectangular
Hanning
Hamming
Blackman
Weighting
A-weighting
Custom weighting
Averaging
Linear
Exponential
Display reference signals
31 bands
Ionized impulse signal from a low-orbit satellite – courtesy of Los Alamos National Laboratory
Joint Time-Frequency Analysis
Unlike conventional signal analysis technologies, the JTFA (Joint
Time-Frequency Analysis) software examines signals in both the
time and frequency domains simultaneously. JTFA can be
applied in almost all applications in which the FFT is used, such
as biomedical signals, radar image processing, vibration analysis,
machine testing, and dynamic signal analysis. However, with
JTFA you get more information by analyzing the time and
frequency domains simultaneously.
Like the classical Fourier analysis, the JTFA consists of two
major methods – linear and quadratic. The linear algorithms
include short-time Fourier transform (STFT) and Gabor
expansion (inverse STFT). By using these linear transforms, you
can transfer a signal from the time domain into the joint time-
frequency domain and vice versa. It is extremely powerful for
noise reduction. The quadratic methods contain adaptive
spectrogram, Choi-Williams distribution, cone-shaped
distribution, Gabor expansion-based spectrogram (also known
as Gabor spectrogram), STFT-based spectrogram, and Wigner-
Ville distribution. Applying the quadratic transforms, you can
easily see how the power spectrum of a signal evolves over time.
The Gabor spectrogram results in the best compromise between
high resolution and cross-term interference.
Stand-Alone JTFA Application
The JTFA software includes a stand-alone Joint Time-Frequency
Analyzer that does not require specific application software. The
ready-to-run application analyzes stored data files, displays the
spectrogram, and saves the spectrogram to disk. It can save and
recall data and analysis to spreadsheet format. You can choose
from six different types of quadratic JTFA algorithms – Gabor,
short time Fourier transform (STFT), Wigner-Ville, Choi-Williams,
and adaptive spectrogram. You can acquire data using DAQ
hardware and use the JTFA Analyzer for post acquisition analysis.
Using the JTFA Utilities
The JTFA component of this toolset also includes a VI library for use
with LabVIEW to create your own custom analyzer. Several JTFA
algorithms, including quadratic transforms as well as linear
transforms, are delivered in VI source code so you can develop
your own custom applications with LabVIEW and DAQ hardware.
National Instruments
Phone: (512) 794-0100 • Fax: (512) 683-8411 • info@natinst.com • www.natinst.com
99
LabVIEW
Advanced Signal Processing
NEW! Super-Resolution
Spectral Analysis
A primary tool for spectral analysis is the fast Fourier transform
(FFT). For high-resolution spectra, FFT-based methods need a
large number of samples. However, in many cases the data set
is limited because of a genuine lack of data, or because you
need to ensure that the spectral characteristics of the signal do
not change over the duration of the data record. For cases
where the number of data samples is limited, you can use
model-based analysis to determine spectral characteristics.
Using this technique, you can assume a suitable signal model
and determine the coefficients of the model. Based on this
model, you can then predict the missing points in the given finite
data set to achieve high-resolution spectra. In addition, model-
based methods can also be used for estimating the amplitude,
phase, damping factor, and frequency of damped sinusoids.
Super-resolution spectral analysis can be used in diverse
applications including biomedical research, economics,
geophysics, noise, vibration and speech analysis.
Using the Super-Resolution Spectral
Analysis Utilities
You can also construct your own custom applications in
LabVIEW with a VI library of the most efficient and common
algorithms such as covariance, principle component auto-
regression (PCAR), Prony’s method, and the matrix-pencil
method. Some of these methods have not been commercially
available before the release of this toolset. Using these VIs, you
can perform both super-resolution analysis and modal-analysis.
Moreover, VIs provided can easily be tailored for many other
signal analysis applications, such as system identification and
linear prediction.
Spectral Analysis Algorithms
Covariance
Principle component auto-regressive (PCAR)
Prony’s method
Matrix-Pencil method
Maximum Description Length
Using the Super-Resolution Spectral
Analysis Application
You can use the spectral analysis stand-alone application to test
the different algorithms for model-based analysis. You can
choose to use simulated data or real-world data acquired using
National Instruments DAQ hardware. You can experiment using
different model-based analysis methods such as the Prony’s
method or the Matrix-Pencil method, and different windowing
techniques such as Hanning, Hamming and Blackmann.
100
National Instruments
Phone: (512) 794-0100 • Fax: (512) 683-8411 • info@natinst.com • www.natinst.com
LabVIEW
Advanced Signal Processing
Wavelet and Filter Bank Design
Wavelets are a relatively new signal processing method. A
wavelet transform is almost always implemented as a bank of
filters that decompose a signal into multiple signal bands. It
separates and retains the signal features in one or a few of these
subbands. Thus, one of the biggest advantages of using the
wavelet transform is that signal features can be easily extracted.
In many cases, a wavelet transform outperforms the
conventional FFT when it comes to feature extraction and noise
reduction. Because the wavelet transform can extract signal
features, wavelet transforms find many applications in data
compression, echo detection, pattern recognition, edge
detection, cancellation, speech recognition, texture analysis,
and image compression.
Using the Wavelet and Filter Bank Tools
The key to a creating a successful wavelet application is to select
an appropriate wavelet transform, which is equivalent to
selecting a good set of filters in the filter bank. The wavelet and
filter bank design component of this toolset provides a unified
approach to designing a wavelet transform or filter bank. You
can design an arbitrary wavelet transform through an easy-to-
use graphical user interface. By interactively selecting a wavelet
prototype (equiripple or maxflat) and different FIR filter
combinations, you can easily find the best wavelet or filter bank
for your application. The end result is a wavelet or filter bank
design that works for your application and meets your design
specification. The wavelet and filter bank design tools apply to
1D signals and to 2D images as well. The signal or image can be
loaded from a data file or acquired and processed in real time
using DAQ or IMAQ hardware.
You can graphically design wavelet and filter banks using the
stand-alone application. You can save all design results as text
files for use in other applications. The toolset also includes
wavelet analysis VIs, such as 1D and 2D analysis and synthesis
filters, as well as many other useful functions for use in building
custom LabVIEW applications.
VirtualBench DSA
VirtualBench DSA features an easy-to-use GUI that simplifies the
measurement of power spectrum, amplitude spectrum,
coherence, transient capture, cross spectrum, and total
harmonic distortion (THD). Plus, you can use VirtualBench-DSA
as a low frequency oscilloscope to view signals in the time and
frequency domains simultaneously.
Additional Signal Processing Resources
The National Instruments Signal Processing course is designed to
teach the basic and advanced signal processing capabilities of
LabVIEW and the Signal Processing Toolset. Please see page 847 for
more details on the course.
The book LabVIEW Signal Processing by Abhay Samant,
Mahesh Chugani, and Michael Cerna, published by Prentice
Hall, is a practical guide to the signal processing and
mathematical capabilities of LabVIEW. You can use this book to
review classical DSP theory, build practical applications and
enrich your knowledge using real-world applications. For more
information, please visit the Prentice Hall web site at
www.phptr.com
or call (800) 947-7700 (U.S.) or (201) 767-
4990 (International) to order the book directly from Prentice Hall
(ISBN 0-13-972449-4).
Wavelet designs
Orthonormal
Maximum Flat (such as Daubechies wavelets)
Equiripple
Biorthonormal
Maximum Flat (such as B-spline wavelets)
Ordering Information
Signal Processing Toolset for LabVIEW/BridgeVIEW
Windows NT/98/95 ....................................777136-01
National Instruments
Phone: (512) 794-0100 • Fax: (512) 683-8411 • info@natinst.com • www.natinst.com
101
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