[Mne_analysis] downsampling in bdf file

[Liu Mengting]

Ya, I opened it with matlab, see the events, there appears some more event
(probably twice more), but the original events are well kept (both the
temporal point and event id are both kept). However in MNE, it appears 100
times more events than there should be and all their temporal order and
events id are both messed up.

There is also a error as below:

ValueError: You have 77499 events shorter than the shortest_event.
These are very unusual and you may want to set min_duration to a larger
value e.g. x / raw.info['sfreq']. Where x = 1 sample shorter than the
shortest event length.


Thanks,

Mengting

2015-01-14 15:31 GMT-05:00 Eric Larson <larson.eric.d at gmail.com>:

> I'm not familiar with the edfbrowser routines, but if they use standard
> low-pass-downsample methods instead of a zero-order hold for the stimulus
> channel, the low-pass filter ringing will produce many errant events. When
> you say that you tested the file using MATLAB, you mean that you opened it?
> Did you look at the stimulus channel to see if the resampling introduced
> ringing?
>
> Cheers,
> Eric
>
>
> On Wed, Jan 14, 2015 at 12:24 PM, Liu Mengting <bigting84 at gmail.com>
> wrote:
>
>> Hi MNE users,
>>
>> I am tring to use MNE python to process the bdf EEG file. Since our data
>> is huge, so I first downsampled using the edfbrowser which is a bdf
>> processing software, then I loaded the downsampled data using
>> read_raw_edf(), but I found that the STI channel was totally messed up, I
>> can find far more events than there should be.
>>
>> To make sure the file is good, I tested using matlab and everything works
>> well, do you guys have any idea what is going on please?
>>
>> Thanks and appreciate,
>>
>> Mengting
>>
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