[FieldTrip] A problem in real-time processing of MEG signal using field trip buffer

Soheila Samiee sla.samiee at gmail.com
Mon Feb 20 17:21:58 CET 2012

Dear Jörn,

   Thanks for your answer. I use CTF/VSM MedTech System. I use 364 channels
and the sampling rate is 1200. The decimation rate is 1.
    As I saw in my recording there are two reasons for crashing in matlab
session one of them is about transferring data which rarely occurs when the
system is freshly restarted and the second one is related to reading data
from buffer. When the number of samples of data which should be read is
high we may see such problem.
    I wanted to check the timing of MEG System data stream and I used a
m-file similar to what is published in fieldtrip website (
I attach the mfile to this email. When I run it step by step there is no
problem, but when I run the whole file the problem of crashing matlab is
occurred exactly when "i=2"  and we are on the line of reading the data (*dat
= buffer('get_dat', [s(i-1),s(i)],host,port); *). The problem occurs even
if I restarted the computer just before running this file.
    On the other hand, although when the computer is freshly restarted we
won't see any crash in matlab session during transferring data, but
sometimes we see the message of "*Internal Converter thread does not keep
up with load*" in the *acq2ft *terminal in acquisition system. This problem
is depend on the rate of sending the data which is related to number of the
channels and sampling rate, when we have more sampling rate or more number
of channels we will see this message more times and when this message show
on the screen, no data transfer to field trip buffer and we can't read data
on the other computer.

I appreciate it if you help me solve both of these problems about matlab
crash and error in data transferring.

All the best,

On Thu, Feb 16, 2012 at 4:36 AM, "Jörn M. Horschig" <
jm.horschig at donders.ru.nl> wrote:

>  Dear Soheila,
> we were facing the same problem here. Presumably, there is some problem in
> the shared memory module that the buffer is using. Right now, however, we
> could not find out where the error precisely comes from, so our best work
> around is to restart the computer prior recording and optimize settings,
> such as channels and sampling/decimation rate of acq2ft. In our lab, we
> managed to find near-optimal settings, so that the buffer crashes only
> rarely (actually, I never saw it crashing when the acquisition computer was
> freshly restarted). Note that a lower number of channels or higher
> decimation does not mean that it runs more stable.  It seems to be
> literally a trial-and-error approach :/
> In order to track this down further, we need some more information, e.g.
> what MEG system are you using? What's your sampling rate, how many channels
> do you put into the buffer, and what's your decimation rate? It would be
> great if you could send me that information so that we can maybe try to
> track this down.
> Best regards,
> Jörn
> On 2/14/2012 5:42 PM, Soheila Samiee wrote:
> Dear group,
> I use FieldTrip for real-time processing of MEG signals using shared
> memory and field trip buffer in a machine other than acquisition system. I
> use matlab for reading the buffer and processing the data.
> During my data acquisition and sending it to other computer with *acq2ft*in linux, I face a problem. After sending some blocks of data, this
> message: "*Internal Converter thread does not keep up with load*" is
> shown in the terminal of *acq2ft* and in my matlab session I see an error
> : "ERROR: the buffer returned an error (517)". It does not depend on
> sampling rate of data in acquisition system. The problem often solve when I
> restart the computer which receives the data, but after some minutes of
> transferring the data I see the message again.
> Would you please help me in solving this problem?
> Best Wishes,
> Soheila
> _______________________________________________
> fieldtrip mailing listfieldtrip at donders.ru.nlhttp://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> --
> Jörn M. Horschig
> PhD Student
> Donders Institute for Brain, Cognition and Behaviour
> Centre for Cognitive Neuroimaging
> Radboud University Nijmegen
> Neuronal Oscillations Group
> P.O. Box 9101
> NL-6500 HB Nijmegen
> The Netherlands
> Contact:
> E-Mail: jm.horschig at donders.ru.nl
> Tel:    +31-(0)24-36-68493
> Web: http://www.ru.nl/donders
> Visiting address:
> Trigon, room 2.30
> Kapittelweg 29
> NL-6525 EN Nijmegen
> The Netherlands
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
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