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LabVIEW高级信号处理工具包手册.pdf
Time Frequency Analysis Tools User Manual
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Contents
About This Manual
Conventions
Related Documentation
Chapter 1 Introduction to Time-Frequency Analysis
Figure 1-1. Speech Signal
Figure 1-2. Power Spectrum of Speech Signal
Figure 1-3. STFT Spectrogram of Speech Signal
Common Time-Frequency Analysis Applications
Overview of Time Frequency Analysis Tools
Finding Example VIs
Related Signal Processing Tools
Chapter 2 Understanding Linear Time-Frequency Analysis Methods
Short-Time Fourier Transform
Window Type and Window Length
Discrete Gabor Transform and Expansion
Figure 2-1. Using Discrete Gabor Transform and Discrete Gabor Expansion
Figure 2-2. Time-Frequency Representation of Noisy Chirps
Figure 2-3. Denoised Chirps
Adaptive Transform and Expansion
Figure 2-4. Equally Sampled Grid
Figure 2-5. Using Adaptive Transform and Adaptive Expansion
Figure 2-6. Complex Signal from Pulse Radar Receiver
Figure 2-7. STFT Magnitude Spectrum of Radar Signal in Figure 2-6
Figure 2-8. Reconstructed Target Signature with Sea Clutter Removed
Figure 2-9. STFT Magnitude Spectrum of Reconstructed Target Signature
Comparing Linear Time-Frequency Analysis Methods
Table 2-1. Linear Time-Frequency Analysis Method Properties
Chapter 3 Understanding Quadratic Time-Frequency Analysis Methods
STFT Spectrogram
Figure 3-1. Frequency Hopper Signal
Figure 3-2. Ideal Time-Frequency Representation of the Hopper Signal
Figure 3-3. STFT Spectrogram of the Hopper Signal (Window Length = 128)
Figure 3-4. STFT Spectrogram of the Hopper Signal (Window Length = 32)
Figure 3-5. STFT Spectrogram of the Hopper Signal (Window Length = 256)
Reassignment Method
Figure 3-6. Reassigned STFT Spectrogram of the Hopper Signal
Wigner-Ville Distribution
Figure 3-7. WVD of the Hopper Signal
Figure 3-8. WVD of the Analytic Hopper Signal
Other Cohen’s Class Time-Frequency Distributions
Figure 3-9. Ambiguity Function of the Hopper Signal
Choi-Williams Distribution
Figure 3-10. Exponential Kernel Function
Figure 3-11. CWD of the Hopper Signal
Cone-Shaped Distribution
Figure 3-12. Cone-Shaped Kernel Function
Figure 3-13. CSD of the Hopper Signal
Gabor Spectrogram
Figure 3-14. Gabor Spectrogram of the Hopper Signal (Order = 0, Window Length = 128)
Figure 3-15. Gabor Spectrogram of the Hopper Signal (Order = 20, Window Length = 128)
Figure 3-16. Gabor Spectrogram of the Hopper Signal (Order = 3, Window Length = 128)
Figure 3-17. Signal with Three Gaussian Components
Figure 3-18. Gabor Spectrogram of the Composite Gaussian Signal (Order = 5, Window Length = 32)
Figure 3-19. Gabor Spectrogram of the Composite Gaussian Signal (Order = 5, Window Length = 256)
Adaptive Spectrogram
Figure 3-20. Simulated Chirplet Signal
Figure 3-21. Adaptive Spectrogram of the Simulated Chirplet Signal
Figure 3-22. Gabor Spectrogram of the Simulated Chirplet Signal (Order = 2, Window Length = 256)
Spectrogram Feature Extraction
Mean Instantaneous Frequency
Mean Instantaneous Bandwidth
Group Delay
Marginal Integration
Creating Quadratic Time-Frequency Analysis Applications
Figure 3-23. Typical Approach for Creating Applications Using Quadratic Time-Frequency Analysis
Comparing Quadratic Time-Frequency Analysis Methods
Table 3-1. Quadratic Time-Frequency Analysis Method Properties
Calculating the Energy of a Signal at Each Time-Frequency Instant
Figure 3-24. STFT Spectrogram (Hanning Window)
Figure 3-25. Gabor Spectrogram (Order = 4)
Appendix A Technical Support and Professional Services
LabVIEWTM
Advanced Signal Processing Toolkit
Time Frequency Analysis Tools User Manual
Time Frequency Analysis Tools User Manual
June 2008
371552B-01
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Contents
About This Manual
Conventions ...................................................................................................................ix
Related Documentation..................................................................................................x
Chapter 1
Introduction to Time-Frequency Analysis
Common Time-Frequency Analysis Applications ........................................................1-4
Overview of Time Frequency Analysis Tools...............................................................1-5
Finding Example VIs.......................................................................................1-6
Related Signal Processing Tools....................................................................................1-6
Chapter 2
Understanding Linear Time-Frequency Analysis Methods
Short-Time Fourier Transform ......................................................................................2-2
Window Type and Window Length ................................................................2-3
Discrete Gabor Transform and Expansion.....................................................................2-4
Adaptive Transform and Expansion ..............................................................................2-7
Comparing Linear Time-Frequency Analysis Methods ................................................2-13
Chapter 3
Understanding Quadratic Time-Frequency Analysis Methods
STFT Spectrogram.........................................................................................................3-2
Reassignment Method .....................................................................................3-6
Wigner-Ville Distribution..............................................................................................3-7
Other Cohen’s Class Time-Frequency Distributions.....................................................3-10
Choi-Williams Distribution .............................................................................3-11
Cone-Shaped Distribution ...............................................................................3-13
Gabor Spectrogram ........................................................................................................3-14
Adaptive Spectrogram ...................................................................................................3-20
Spectrogram Feature Extraction ....................................................................................3-22
Mean Instantaneous Frequency .......................................................................3-23
Mean Instantaneous Bandwidth ......................................................................3-23
Group Delay ....................................................................................................3-23
Marginal Integration........................................................................................3-24
Creating Quadratic Time-Frequency Analysis Applications.........................................3-24
Comparing Quadratic Time-Frequency Analysis Methods ...........................................3-25
Calculating the Energy of a Signal at Each Time-Frequency Instant............................3-27
© National Instruments Corporation
v
Time Frequency Analysis Tools User Manual
Contents
Appendix A
Technical Support and Professional Services
Time Frequency Analysis Tools User Manual
vi
ni.com
About This Manual
This manual contains a brief introduction to time-frequency analysis,
includes information about linear and quadratic methods of time-frequency
analysis, and describes how to develop typical applications by using the
LabVIEW Time Frequency Analysis Tools.
This manual requires that you have a basic understanding of the LabVIEW
environment. If you are unfamiliar with LabVIEW, refer to the Getting
Started with LabVIEW manual before reading this manual.
Note This manual is not intended to provide a comprehensive discussion of
time-frequency analysis. Refer to Introduction to Time-Frequency and Wavelet
Transforms1 for more information about time-frequency analysis.
Conventions
»
bold
italic
monospace
The following conventions appear in this manual:
The » symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a note, which alerts you to important information.
Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names.
Italic text denotes variables, emphasis, a cross-reference, or an introduction
to a key concept. Italic text also denotes text that is a placeholder for a word
or value that you must supply.
Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.
1 Qian, Shie. Introduction to Time-Frequency and Wavelet Transforms. Upper Saddle River, New Jersey: Prentice Hall PTR,
2001.
© National Instruments Corporation
ix
Time Frequency Analysis Tools User Manual
About This Manual
Related Documentation
The following documents contain information that you may find helpful as
you read this manual:
•
LabVIEW Help, available by selecting Help»Search the LabVIEW
Help
Getting Started with LabVIEW, available by selecting Start»
All Programs»National Instruments»LabVIEW x.x»
LabVIEW Manuals, where x.x is the version of LabVIEW you
installed, and opening LV_Getting_Started.pdf. This manual also
is available by navigating to the labview\manuals directory and
opening LV_Getting_Started.pdf. The LabVIEW Help includes
all the content in this manual.
LabVIEW Fundamentals, available by selecting Start»All Programs»
National Instruments»LabVIEW x.x»LabVIEW Manuals, where
x.x is the version of LabVIEW you installed, and opening
LV_Fundamentals.pdf. This manual also is available by navigating
to the labview\manuals directory and opening
LV_Fundamentals.pdf. The LabVIEW Help includes all the content
in this manual.
Note The following resource offers useful background information on the general
concepts discussed in this documentation. This resource is provided for general
informational purposes only and is not affiliated, sponsored, or endorsed by National
Instruments. The content of this resource is not a representation of, may not correspond to,
and does not imply current or future functionality in the Time Series Analysis Tools or any
other National Instruments product.
Qian, Shie. Introduction to Time-Frequency and Wavelet Transforms.
Upper Saddle River, New Jersey: Prentice Hall PTR, 2001.
Time Frequency Analysis Tools User Manual
x
ni.com
Introduction to Time-Frequency
Analysis
1
One way to represent a signal is the time-domain waveform, which shows
how the amplitude of the signal changes over time. Examples of
time-varying signals include the temperature in temperature logs,
stock-index profiles, electrocardiogram signals, vibration signals, and
speech signals, such as the speech signal in Figure 1-1.
Figure 1-1. Speech Signal
The time-domain speech waveform in Figure 1-1 depicts how the
sound-pressure level evolves over time. The higher the sound-pressure level
at any particular time, the larger the magnitude, or the absolute value, of the
signal.
An important task in most speech-enhancement applications is to find the
noise characteristics and then remove the noise from the speech signal. In
Figure 1-1, the period from 1.4 s to 2.0 s is the silence period, when no
speech is present. Any signal measured during this time frame is noise. In
speech-enhancement applications, you often observe the signal during the
silence periods to estimate the noise characteristics.
© National Instruments Corporation
1-1
Time Frequency Analysis Tools User Manual
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