Fast Fourier Transform (FFT) is the easiest way to show the dominant frequencies in a signal. FFT is an efficient algorithm to compute the discrete Fourier Transform and in its inverse. There are many distinct FFT algorithms which involves a wide range of mathematics, which starts from simple complex-number arithmetic to group theory and number theory too. You also need Microsoft Excel with the Data Analysis package.If you don’t have this you can install this under Tools or Add-ins.
In this article you will see how to perform a FFT graph in Microsoft excel.
First and foremost open a blank spreadsheet and then follow the following titles to the first cells in column A, B, C, D and E of your spreadsheet: Time, Data, FFT Frequency, FFT Complex, and FFT Magnitude.
You need to add your data to the “Data” column. It will be helpful for you to make a note of the number of data points that is samples in your list and taking into consideration the sampling rate at which your data is taken. Do not forget o write and label these two numbers somewhere in your spreadsheet.
In the “Time” column, you need to determine the time at which each point was taken. The easiest way to do this is to divide the total time by the number of data points.
Next you need to perform a Fourier Analysis of your data which can be either Data/Data Analysis/ Fourier Analysis. You have make sure that the input range is your entire data column and the output range is you entire FFT Complete column. This column is known as FFT Complex column because the Fourier Analysis function outputs a complex number.
In the very first cell of the “FTT Magnitude” column, you need to type the following equation: =IMABS (E2)
Now you need to drag this equation down so that it fills every cell in this column. This will turn all the complex numbers in the “FTT Complex” column into a real number so that we can use the dominant frequencies.
Now we need to calibrate the axis A of the graph to show the dominant frequencies. It may prove beneficial if we create a separate column showing zero through the number of data points minus one (N-1). It will also help to create a separate cell with the following function:
=(S/2)/ (N/2) over here S is a sampling rate and N is the number of samples.
In the “FTT Frequency” column you need to type the following function:
Here F2 is the appropriate number from the number column, and $G$4 denotes the function dividing the sampling rate by the number of samples. Now drag this function down to half of your data of your data points.
Now create a graph of “FTT Magnitude” column (Y axis) versus the “FTT Frequency” column (X axis). If all you have done is right then you should get a graph with peaks where the dominant frequencies are.