Digital
Filters Option
The new 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 6847.
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 6847 for crash
test analysis
To purchase this FlexPro option, click
here or contact your local Adept Scientific
office. |
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