# How to remove (or isolate) side peaks except main peak after FFT

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Hyeon-Taek 2024년 4월 17일
답변: Star Strider 2024년 4월 17일
Hi All,
I have a data as above. This is some data from optical interferometry. After cropping the noise level (for getting dominant oscillation as best as I can), I can get the frequency data like below after FFT.
Like the fft data, there is a side peak. Sometimes more than one side peak. Also, not good the noise level as you can see. (Of course I have to get better raw data.)
Here is my questions.
Q1. How can the side peak be removed or isolated? I want to get the main peak only.
Q2. Is it available SVD function for the data?
Please let me know if whoever can let me recommend any examples for the questions. BR, Taek

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### 답변 (2개)

Chunru 2024년 4월 17일
You can try "findpeaks" and using "MinPeakDistance" option.
doc findpeaks
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Star Strider 2024년 4월 17일
Using:
NFFT = 2^nextpow2(numel(signal))
and a window function (for example hann) in the fft call could improve the fft result:
FTsignal = fft((signal(:)-mean(signal(:)) .* hann(numel(signal)), NFFT)/sum(hann(numel(signal)));
Then, plot the absolute value of that result, and also use it for the argument to findpeaks. (All of this assumes that ‘signal’ is a vector.)

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