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The FlexPro Digital Filters option provides you with the latest design techniques for simple operation. The FlexPro Analysis Wizard merges steps for filter design, filtering and presentation into a simple sequential process. Using real-time 2D and 3D graphics, FlexPro offers you immediate visual feedback whenever any change is made to the filter specification.
Enhanced IIR Filters
IIR filters include internal feedback (recursive filters) and provide a high degree of steepness with a short filter length. This makes it possible to design lowpass, highpass, bandpass and bandstop filters. The Digital Filters Option extends the basic set of Bessel, Butterworth and Chebyshev filters in FlexPro Standard/Professional to include Inverse Chebyshev (Chebyshev II) and Elliptic (Cauer) filter characteristics. The various filters are optimized for phase linearity, minimal ripple of the transition function, or high slope steepness. You can calculate the filter order by predefining the width of the transition instead of the order. The ripple of the amplitude response can be adjusted for the Chebyshev and Elliptic filters.
FIR Filter Design
FIR filters avoid feedback and are therefore always stable. FlexPro offers you two procedures for calculating phase-linear filters with a minimum filter length.
FIR Filter Design Using the Window Method
This method uses the Rectangular, Bartlett, Hamming Generalized Hamming, Hanning, Blackman, Kaiser and Chebyshev windows familiar from spectral analysis. These windows are used to limit the filter's impulse response to the desired length. You can use this method to design lowpass, highpass, bandpass and bandstop filters. Use the Kaiser or Chebyshev windows to specify the filter's length, attenuation and transition width more precisely. You only have to provide two parameters, and the third parameter is calculated automatically.
FIR Filter Design Using the Equiripple Method
This is the most powerful design method for FIR filters with constant ripple (equiripple). In addition to the standard lowpass, highpass, bandpass and bandstop filters, you can use this method to design any type of multiband filter. You divide the frequency range in an adjustable number of bands with constant or linear amplitude and transitions located in between. You can predefine the approximation error or the maximum ripple separately for each band. FlexPro then calculates the FIR filter with the minimum length based on your specification. Alternatively, you can even predefine any continuous curve as the filter's amplitude response. You can save your filter specifications as templates and re-use them.
Smoothing Filters
The Savitzky-Golay smoothing filter uses local regression instead of the common moving average calculation. Use this filter to smooth signals whose peaks are to be preserved as purely as possible.
LOESS and LOWESS filters are very popular smoothing methods that use a locally weighted regression function. The weighting causes distant points to have less influence on a smoothed value than with moving average smoothing.
The Loess filter uses a quadratic weighting function, and the Lowess filter uses a linear weighting function.
CFC Filter
CFC is short for Channel Frequency Class. This involves a 4-pole phaseless Butterworth filter. The CFC filter is used for crash tests in particular. It is implemented in accordance with ISO 6487.
Documentation
The Digital Filters option includes extensive online documentation. All analysis objects, functions and algorithms are described in detail. A variety of references gives you an overview of the essential reference material.
You can become familiar with the procedures for designing filters through an easy-to-understand tutorial.
Features
IIR Filter Design
- Filter types: lowpass, highpass, bandpass and bandstop
- Characteristics: Bessel, Butterworth, Chebyshev, Inverse Chebyshev, Elliptic/Cauer
- Adjustable approximation errors or ripple / attenuation for Chebyshev and Elliptic filters.
- Optional phase correction through reverse filtering
- Capability to calculate filter order for a defined specification
FIR Filter Design Using the Window Method
- Filter types: lowpass, highpass, bandpass and bandstop
- Window types: Rectangular, Bartlett, Hamming, Generalized Hamming, Hanning, Blackman, Kaiser and Chebyshev
- Filters can be specified more precisely with filter length, attenuation or transition width when using Chebyshev or Kaiser windows
- Linear phase with optional phase correction
FIR Filter Design Using the Equiripple Method (Remez-Exchange, Parks-McClellan)
- Filter types: lowpass, highpass, bandpass, bandstop and multiband
- Frequency response with any number of steps and ramps
- Individually adjustable errors/ripple for all bands
- Alternatively, any continuous curve can be specified as amplitude response
- Leads to optimum filter for predefined specification
- Filter specifications can be saved as templates
- Linear phase with optional phase correction
Smoothing Filters
- Savitzky-Golay filter with minimal damping of peaks in the signal
- Loess and Lowess filters with a weighted regression function
CFC Filter
- Channel Frequency Class filter in accordance with ISO 6487 for crash test analysis
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