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What is the Subband Filter VI in the LabVIEW JTFA Toolkit?

Primary Software: LabVIEW Development Systems>>LabVIEW Full Development System
Primary Software Version: 7.1
Primary Software Fixed Version: N/A
Secondary Software: LabVIEW Toolkits>>Advanced Signal Processing Toolset

Problem: What is the Subband Filter VI in the LabVIEW JTFA Toolkit?

Solution: The SubBand VI can be thought as a regular bandpass filter. The differences from the conventional bandpass filter are:

  1. For the decimation convenience, the pass band is limited to two's power, such as full-band, half-band, etc.
  2. The output is decimated according to the width of pass band. There is no decimation for full band. For half band, the OUTPUT is decimated by two. For quarter band, the OUTPUT is decimated by four. In other words, only every fourth output data is sampled. Note that we decimate the output not the input data. So, in any cases, all the input data are used.


The start frequency control gives the user a flexibility of selecting his/her desired frequency band. When half band is selected, the frequency range of output is:
f0 to (f0 + fs/4), where f0 and fs denote the start frequency and sampling frequency, respectively.

The process works roughly as follows:

When the start frequency f0 is larger than zero, first we apply a highpass filter to remove all frequency components
that are less than f0. Then, "translate" the rest portion into 0 to (fs/2-f0), where fs denotes the sampling frequency. Now, we remember 0 as f0. Finally, apply a bandpass filter to obtain a desired frequency bandwidth. The entire process takes place
in the frequency domain. All "filters" involved are not traditional digital filters, such as Butterworth, Bessel, Elliptical, etc..

If you need to know more about JTFA, please consult the recent book, "Joint Time-Frequency Analysis" by S. Qian and D. Chen, Prentice-Hall, 1996.

Note: LabVIEW and LabWindows/CVI both offer a solution for measuring transient signals and signals whose frequency components change over time. The Signal Processing Toolset consists of three major areas:
  • Joint time-frequency analysis (JTFA)
  • Super-resolution spectral analysis
  • Wavelet analysis

The product page is linked below.

Related Links: NI LabVIEW Advanced Signal Processing Toolkit


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Report Date: 10/30/2003
Last Updated: 02/24/2006
Document ID: 32TBJC5Z

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