- ‘To see the list of System objects you can pass to the cascade method, type dsp.FilterCascade.helpSupportedSystemObjects’
How do you design a filter cascade with 4 filters total?
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I am looking to pass raw time-series data through a sequence of 4 filters. I've attempted to construct a filter cascade using the DSP Systems Toolbox, but the resulting Bode diagram doesn't make sense. Additionally, the filtered signal has a considerable reduction in amplitude (~10000x smaller than the original). I am assuming there is a way to correct this in the gain settings?
I would ideally like to combine filters H2 & H3 to act as one bandpass filter and H1 and H4 as another. I chose to employ four distinct HP/LP filters, rather than 2 bandpass filters, because they have different orders. Let me know if I need to clarify anything. Thanks.
H1 = dsp.LowpassFilter('FilterType', 'IIR','FilterOrder',3, 'NormalizedFrequency', false, 'PassbandFrequency', 85, 'StopbandFrequency', 95, 'SampleRate', 500, 'DesignForMinimumOrder', false);
H2 = dsp.LowpassFilter('FilterType', 'IIR','FilterOrder',1, 'NormalizedFrequency', false, 'PassbandFrequency', 120, 'StopbandFrequency', 130, 'SampleRate', 500, 'DesignForMinimumOrder', false);
H3 = dsp.HighpassFilter('FilterType', 'IIR','FilterOrder',2, 'NormalizedFrequency', false, 'StopbandFrequency', 0.1, 'PassbandFrequency', 1, 'SampleRate', 500, 'DesignForMinimumOrder', false);
H4 = dsp.HighpassFilter('FilterType', 'IIR','FilterOrder',1, 'NormalizedFrequency', false, 'StopbandFrequency', 0.1, 'PassbandFrequency', 4, 'SampleRate', 500, 'DesignForMinimumOrder', false);
Final_Filter = dsp.FilterCascade(H2,H3, H1, H4);
3 个评论
Paul
2024-4-1
Would be helpful to get more information, like why you think the Bode diagram doesn't make sense, and the input for which you think the output is incorrect.
Also, when I ran this in 2022a, all four calls resulted in the warning:
Warning: The StopbandFrequency property is not relevant in this configuration of the System object.
Do you see that as well? If so, it might be a clue that that H1-H4 might not be yielding the expecte responses. Hard to say without knowing more on what the end goal is.
Sam Chak
2024-4-1
@G, The order of the IIR filter is probably too low to meets the filter design specifications. If it is acceptable to let the DSP to auto-design the minimum order filter that meets the filter design specifications, then try the following:
H1 = dsp.LowpassFilter('FilterType', 'IIR', ...
'DesignForMinimumOrder', true, ...
'PassbandFrequency', 85, ...
'StopbandFrequency', 95, ...
'SampleRate', 500)
H2 = dsp.LowpassFilter('FilterType', 'IIR', ...
'DesignForMinimumOrder', true, ...
'PassbandFrequency', 120, ...
'StopbandFrequency', 130, ...
'SampleRate', 500)
H3 = dsp.HighpassFilter('FilterType', 'IIR', ...
'DesignForMinimumOrder', true, ...
'PassbandFrequency', 1, ...
'StopbandFrequency', 0.1, ...
'SampleRate', 500)
H4 = dsp.HighpassFilter('FilterType', 'IIR', ...
'DesignForMinimumOrder', true, ...
'PassbandFrequency', 4, ...
'StopbandFrequency', 0.1, ...
'SampleRate', 500)
Final_Filter = dsp.FilterCascade(H2, H3, H1, H4)
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