sampling rate and fft
显示 更早的评论
Do I need to specify the sampling rate when using FFT? I am wanting to look at frequency response of a signal, and am getting crazy frequency response, way above sampling rate. Sorry for a very basic question, trying to get up to speed.
采纳的回答
Wayne King
2014-2-5
编辑：Wayne King
2014-2-5
No, you don't need to specify the sampling rate, but if you wish to create a meaning frequency vector, then you need to know the sampling rate.
For example:
Fs = 1000; % sampling rate of 1000 Hz
t = 0:1/Fs:1-1/Fs;
x = cos(2*pi*100*t)+randn(size(t));
xdft = fft(x);
xdft = xdft(1:length(x)/2+1);
DF = Fs/length(x); % frequency increment
freqvec = 0:DF:Fs/2;
plot(freqvec,abs(xdft))
so the output of fft() is agnostic about frequency, but if you want to interpret that output in physical frequencies, then you need to know the sampling rate.
3 个评论
Reed
2014-2-6
Wayne King
2014-2-6
I am eliminating 1/2 of the fft() output since it is redundant for a real-valued signal if you are just interested in plotting the magnitude.
The syntax above works for an even length signal without warning is your x, your signal an odd number of samples in length?
If that is the case, do
xdft = xdft(1:floor(length(x)/2)+1);
Reed
2014-2-6
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Transforms 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
