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Filter Sound from Data

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Sam Hurrell
Sam Hurrell 2022-2-22
评论： Star Strider 2022-2-22
I have frequency-based data sets (with column 1 for time and column 2 for amplitude), and I use the following code to filter out the sound. I'm not convinced that this is the most effective system as I believe this process changes the time at which other signals occur. Is there a better system for filtering data?
BP = [0.8725 0.8925]; %Frequency filter band
Fs = 1/(data(2,1)-data(1,1)); %Sampling Freq.
Y00 = bandpass(data(:,2),BP,Fs); %Filtered data

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回答（2 个）

Jan
Jan 2022-2-22
filtfilt works without shifting the data.
Star Strider
Star Strider 2022-2-22
That appears to me to be correct.
If you are using the same filter for all the data sets, return the digital filter object after the first set:
[Y00,df] = bandpass(data(:,2),BP,Fs, 'ImpulseResponse','iir'); %Filtered data
to design an elliptic filter (see ellip for details) and return it as well.
Then in subsequent data sets, use it with filtfilt to do the filtering:
Y01 = filtfilt(df, data2(:,2));
That elimiinates the computational expense of designing the same filter for each signal.
.
  2 个评论
Sam Hurrell
Sam Hurrell 2022-2-22
Apologies as I am not well versed in Matlab, but what dyou mean by "return the digital filter", and how does this work with filtfilt?
Star Strider
Star Strider 2022-2-22
Ran in:
The bandpass and related functions optionally return the digital filter object they created as the second output. See for example the Bandpass Filter Steepness section of the documentation.
data = randn(500,2); % Create Matrix
data(:,1) = linspace(0, 499, 500)'/100;
data2 = randn(500,2); % Create Matrix
t = data(:,1);
BP = [0.8725 0.8925]; %Frequency filter band
Fs = 1/(data(2,1)-data(1,1)); %Sampling Freq.
[Y00, df] = bandpass(data(:,2),BP,Fs,'ImpulseResponse','iir'); %Filtered data
Y01 = filtfilt(df, data2(:,2));
figure
plot(t, Y00)
grid
figure
plot(t, Y01)
grid
The data are synthetic, however the code demonstrates the correct procedure.
.

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