[FieldTrip] problem with ft_resampledata after ft_preprocessing (inc. Hilbert)

[Elisa Carrus]

Ah, that's it! I should have set demean to 'no'.

Thanks!

On 28/04/2014 16:32, Julian Keil wrote:
> Hi Elisa,
>
> did you check your .cfg of the output for demean and detrend?
> Depending on the FT-Version you use, the defaults may be to demean and 
> detrend your data which might center the data around 0.
>
> See the help of your fr_resampledata-function for more info.
>
> Best,
>
> Julian
>
>
> ********************
> *Dr. Julian Keil*
> *
> *
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> Am 28.04.2014 um 16:52 schrieb Elisa Carrus:
>
>> Hi FT users,
>>
>> I am having some problems with resampling (downsampling) the data.
>>
>> Here is what I'm doing:
>>
>> I preprocess the continuous data to obtain band-pass filtered signal 
>> in several frequencies (4-8,8-12,12-30, etc), also taking the abs 
>> value of the Hilbert transform. The absolute value of the Hilbert is 
>> ultimately what I need.
>>
>> I have used the following code:
>> /
>> //cfg = [];//
>> //cfg.channel = 'MEG';//
>> //cfg.demean = 'yes';//
>> //cfg.detrend = 'yes';//
>> //cfg.lpfilter = 'yes';//
>> //cfg.hilbert = 'abs';//
>> //cfg.hpfilter = 'yes';//
>> //cfg.hilbert = 'abs';//
>> //cfg.lpfreq = 30;//
>> //cfg.hpfreq = 12;//
>> //cfg.dataset = '0061_syntask_02_raw_ssst_td.fif';//
>> //cfg.continuous = 'yes';//
>> //beta = ft_preprocessing(cfg);//
>> /
>> After this, I epoch the data as follows
>>
>> /cfg = [];//
>> //cfg.trl = trl2; % this is a trial definition previously created//
>> //beta_ep = ft_redefinetrial(cfg,beta);/
>>
>> and then I downsample as follows:
>>
>> /cfg = [];//
>> //cfg.resamplefs = 500;//
>> //beta_epdw = ft_resampledata(cfg, beta_ep)/
>>
>> I don't encounter any errors, but the strange thing is that the data 
>> looks fine up to before I downsample (i.e.g. if I plot one trial, 
>> it's all positive values, as I would expect from the abs of the 
>> Hilbert), but if I plot the downsampled data, the signal has both 
>> negative and positive values.
>>
>> Is there something I'm missing?
>>
>> Thanks a lot if you can help,
>>
>> Elisa
>>
>>
>>
>>
>>
>>
>>
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>
>
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