MATLAB: Filtering data by removing a specified frequency (noise)

Question

Hi, I have Pressure-crank angle degree data for an Internal Combustion Engine, before combustion starts, the curve is realistic and smooth, after the combustion starts, a pressure wave, of known frequency, travelling through the combustion chamber resulting in disturbing the original pressure increase curve, how can I remove this known frequency from my data ? I tried with fft, butter, and filter but I couldn't done, any kind of help will be greatly appreciated, thanks in advance,

Answer 1

Take the Fourier Transform. Look for the spike at that frequency (252 kHz) and set it to zero. Then inverse transform.

Or, alternatively, you could try a Savitkzy-Golay filter (sgolayfilt in the Signal Processing Toolbox) for a one-liner solution. The SG filter is a sliding polynomial filter - it replaces the element at the center of the sliding window by the polynomial fit, at that location, of the data inside the window. (Demo available upon request.)