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faq:why_does_my_output.freq_not_match_my_cfg.foi_when_using_mtmfft_in_ft_freqanalyis [2017/08/17 11:21]
faq:why_does_my_output.freq_not_match_my_cfg.foi_when_using_mtmfft_in_ft_freqanalyis [2017/08/17 11:21] (current)
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 +{{tag>​faq freq}}
 +===== Why does my output.freq not match my cfg.foi when using '​mtmfft'​ in ft_freqanalyis ===== 
 +The length of your time window determines the spectral resolution. If you have a time window of 1 second, you will get 1 Hz resolution, i.e. you can get estimates of power at integer multiples of 1 Hz. If you have a time window of 1.5 second, you will get a frequency resolution of 1/​1.5=0.6667 Hz. That means that you can estimate power at [0.6667 1.3333 2.0000 2.6667 ...] Hz.
 +You can use the option cfg.pad to zero-pad the data. By making the data longer, you can increase the "​virtual"​ resolution of the Fourier transform and get power estimates on the frequencies of interest. This is handy if your data is for example segmented in windows of 0.9 seconds: padding it to 1.0 seconds gives a more handy frequency axis.