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Ah, that's it! I should have set demean to 'no'.<br>
<br>
Thanks!<br>
<br>
<div class="moz-cite-prefix">On 28/04/2014 16:32, Julian Keil wrote:<br>
</div>
<blockquote
cite="mid:DD77596C-2C65-4B24-A0A5-554912B0FE2B@gmail.com"
type="cite">Hi Elisa,
<div><br>
</div>
<div>did you check your .cfg of the output for demean and
detrend? </div>
<div>Depending on the FT-Version you use, the defaults may be to
demean and detrend your data which might center the data around
0.</div>
<div><br>
</div>
<div>See the help of your fr_resampledata-function for more info.</div>
<div><br>
</div>
<div>Best,</div>
<div><br>
</div>
<div>Julian</div>
<div><br>
</div>
<div><br>
<div>
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<div style="word-wrap: break-word; -webkit-nbsp-mode:
space; -webkit-line-break: after-white-space; "><b>Dr.
Julian Keil</b></div>
<div style="word-wrap: break-word; -webkit-nbsp-mode:
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</b></div>
AG Multisensorische Integration<br>
Psychiatrische Universitätsklinik<br>
der Charité im St. Hedwig-Krankenhaus<br>
Große Hamburger Straße 5-11, Raum E 307<br>
10115 Berlin</div>
<div><br>
Telefon: +49-30-2311-1879<br>
Fax: +49-30-2311-2209 </div>
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href="http://psy-ccm.charite.de/forschung/bildgebung/ag_multisensorische_integration">http://psy-ccm.charite.de/forschung/bildgebung/ag_multisensorische_integration</a></div>
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<div>
<div>Am 28.04.2014 um 16:52 schrieb Elisa Carrus:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
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charset=ISO-8859-1">
<div text="#000000" bgcolor="#FFFFFF"> Hi FT users,<br>
<br>
I am having some problems with resampling (downsampling)
the data.<br>
<br>
Here is what I'm doing:<br>
<br>
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.<br>
<br>
I have used the following code:<br>
<i><br>
</i><i>cfg = [];</i><i><br>
</i><i>cfg.channel = 'MEG';</i><i><br>
</i><i>cfg.demean = 'yes';</i><i><br>
</i><i>cfg.detrend = 'yes';</i><i><br>
</i><i>cfg.lpfilter = 'yes';</i><i><br>
</i><i>cfg.hilbert = 'abs';</i><i><br>
</i><i>cfg.hpfilter = 'yes';</i><i><br>
</i><i>cfg.hilbert = 'abs';</i><i><br>
</i><i>cfg.lpfreq = 30;</i><i><br>
</i><i>cfg.hpfreq = 12;</i><i><br>
</i><i>cfg.dataset = '0061_syntask_02_raw_ssst_td.fif';</i><i><br>
</i><i>cfg.continuous = 'yes';</i><i><br>
</i><i>beta = ft_preprocessing(cfg);</i><i><br>
</i><br>
After this, I epoch the data as follows<br>
<br>
<i>cfg = [];</i><i><br>
</i><i>cfg.trl = trl2; % this is a trial definition
previously created</i><i><br>
</i><i>beta_ep = ft_redefinetrial(cfg,beta);</i><br>
<br>
and then I downsample as follows:<br>
<br>
<i>cfg = [];</i><i><br>
</i><i>cfg.resamplefs = 500;</i><i><br>
</i><i>beta_epdw = ft_resampledata(cfg, beta_ep)</i><br>
<br>
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. <br>
<br>
Is there something I'm missing? <br>
<br>
Thanks a lot if you can help,<br>
<br>
Elisa<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
</div>
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