[FieldTrip] ft_freqanalysis warning after ft_rejectartifact on continous data

Stan van Pelt s.vanpelt at fcdonders.ru.nl
Mon Apr 29 12:49:04 CEST 2013

Dear Jose, You don't need to worry about the warning. When performing operations like redefining trials, the time axes values might change slightly (in the order of microseconds or so, don't know the exact figure), resulting in different time axes for, e.g., different channels. Nowadays, FT recognizes these time differences as being non-intended (it is very unlikely that you on purpose would want trials to start at such small different moments in time), corrects them, and outputs you the warning. So, in your case, the trials in 'trials.time' would have slightly different time values. In freq.time, these should be equal. Best, Stan ----- Oorspronkelijk bericht -----
> Van: "Jose Herrero" <jose.herrero66 at gmail.com>
> Aan: "FieldTrip discussion list" <fieldtrip at science.ru.nl>
> Verzonden: Vrijdag 26 april 2013 16:40:59
> Onderwerp: [FieldTrip] ft_freqanalysis warning after ft_rejectartifact
> on        continous data
> dear Fieldtripers,
> i have cleaned the continuous data manually (ft_databrowser) and then
> rejected artifacts (ft_rejectartifact). Now i am trying to do freq
> analysis on the cleaned data after segmentation (ft_redefinetrial,
> with cfg.length=4;cfg.overlap=0.5). I am getting the folowing warning
> message(see below). I don't get it if i use the original (not
> cleaned) continuous data. Should i be concerned?
> freq = ft_freqanalysis(cfg, trials);
> the input is raw data with 43 channels and 188 trials
> Warning: correcting numerical inaccuracy in the time axes 
> > In utilities\private\warning_once at 116
>   In ft_datatype_raw>fixtimeaxes at 289
>   In ft_datatype_raw at 241
>   In ft_checkdata at 213
>   In ft_freqanalysis at 219 
> processing trials
> processing trial 188/188 nfft: 8000 samples, datalength: 8000 samples,
> 1 tapers
> thanks
> --
> Jose L Herrero, PhD
> Department of Psychiatry
> Columbia University College of Physicians and Surgeons
> Cognitive Neuroscience and Schizophrenia Program
> Nathan S. Kline Institute for Psychiatric Research
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> fieldtrip at donders.ru.nl
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