[Eeglablist] Correct for EGI latency error functions

Michael Boyle mrboyle at live.unc.edu
Tue Oct 13 08:15:36 PDT 2015


According to those two EGI notices:

1. It isn't a hardware filtering issue, it is regarding filters applied to
digitized data.

EEG data from EGI amps are acquired at a single "native" sampling rate (for
the 410 this is 20kHz, I can't speak to the other amplifiers), but these
signals are then "decimated" to provide information at lower sampling
rates. Basically, they sort of sample the digitized data, which will create
aliasing that must be corrected with an anti-aliasing filter before
decimation.

"In the original advisory notice, it was noted that the digital Finite
Impulse Response filters used after analog-to-digital conversion delay the
EEG by a fixed interval"

2. In 400 series amplifiers, the filtering delay is still present and not
accounted for in DIN timing. In the second notice they just validated that
the delay values are the delay values.

"For data acquired with the NA 400, NA 405 and NA 410 amplifiers, there is
no modification to the delay values presented in the original Advisory
Notice."

3. For 300 series amplifiers, whether or not this filtering delay will be
an issue depends on what version of NetStation you use.

"With the NA 300 amplifier, we found that the filter delay is only present
in Net Station version 4.4 and later;"

All quotes come directly from the second EGI notice.

Hope that helps clarify!
Michael


On Tue, Oct 13, 2015 at 2:33 AM Kay Sung <ksung3 at jhmi.edu> wrote:

> Regarding the latency issue, there were actually two announcements about
> the latency issue from EGI (they are attached below).
>
> The original notice says that there was a significant timing delay in most
> of Net Amp models but later they changed it.
>
> I don’t know Isaiah’s codes reflect the most recent announcement from EGI.
>
> In their second announcement, EGI said that they found latency delay only
> in NetAmp 300 model with some specific versions of Netstation.
>
>
>
> See below.
>
>
>
>
>
> *** Original announcement ****
>
>
>
> *Electrical Geodesics, Inc. Advisory Notice:*
>
>
> * Anti-Alias Filter Effects on EEG Timing*
>
>
>
> This advisory notice is to alert users of EGI’s GES 300 and 400 series
> amplifiers to the delay of EEG data inherent in the anti-aliasing filters
> of these amplifiers. These delay values have not been effectively
> communicated to EGI customers and need to be considered when aligning
> events (such as events generated from E-Prime or from digital inputs) to
> the EEG.
>
> The digital Finite Impulse Response filters used prior to A/D conversion
> delay the EEG by a fixed interval. This interval is known for each sampling
> rate and amplifier model:
>
>
> *Sampling Rate*
>
> *NA 300*
>
> *NA 400*
>
> *NA 405*
>
> *NA 410*
>
> 1000 s/s
>
> 8 ms
>
> 36 ms
>
> 36 ms
>
> 13 ms
>
> 500 s/s
>
> 18 ms
>
> 66 ms
>
> 66 ms
>
> 34 ms
>
> 250 s/s
>
> 36 ms
>
> 112 ms
>
> 112 ms
>
> 76 ms
>
> 125 s/s
>
> 72 ms
>
>
>
>
>
>
>
>
> Without adjustment, the EEG is delayed with respect to real time and to
> event markers that are aligned with real time. This delay does not affect
> timing of events manually entered by the user with respect to the EEG
> during acquisition.
>
> Particularly for the Net Amps 400, 405, and 410 models at lower sampling
> rates, the delays may be significant in considering EEG and ERP timing. To
> adjust for this delay, users must add a positive value in the “Offset
> Segment” field in the segmentation tool, in addition to E-Prime Event or
> digital input event (DIN) offsets.
>
> This adjustment is only required for real time events that are recorded
> during acquisition. Events entered during review or from the operations of
> tools after data acquisition are already aligned correctly with the EEG.
>
> To make the delays clear to each user, both the EGI technical manuals and
> EGI Support training will be modified to underscore the importance of
> including these delays in the event alignment and segmentation process. In
> addition, the Net Station software (version 5.1.1) will provide an option
> for automatic adjustment.
>
>
> <http://cts.vresp.com/c/?ElectricalGeodesicsI/25e92832cf/6774d3b846/1bb8b10916/utm_content=gfrishkoff%40gsu.edu&utm_source=VerticalResponse&utm_medium=Email&utm_term=&utm_campaign=Advisory%20Notice%20-%20Anti-Alias%20Filter%20Effects%20on%20EEG%20Timing>Please
> contact EGI support <supportteam at egi.com> for any questions.
>
>
>
>
>
> *** Second announcement ****
>
>
>
>
> *Electrical Geodesics, Inc. Update to Anti-Alias Filter Effects on EEG
> Timing Advisory Notice*
>
> This is an update to an advisory notice issued to users of EGI’s GES 300
> and 400 series amplifiers on the delay of EEG data inherent in the
> anti-alias filters of these amplifiers.
>
> In the original advisory notice, it was noted that the digital Finite
> Impulse Response filters used after analog-to-digital conversion delay the
> EEG by a fixed interval by the following values:
>
>
> *Sampling Rate*
>
> *NA 300*
>
> *NA 400*
>
> *NA 405*
>
> *NA 410*
>
> 1000 s/s
>
>  8 ms (0.52)
>
>  36 ms (0.63)
>
>  36 ms (0.52)
>
>  13 ms (0.52)
>
> 500 s/s
>
>  18 ms (0.63)
>
>  66 ms (1.03)
>
>  66 ms (1.03)
>
>  34 ms (1.10)
>
> 250 s/s
>
>  36 ms (2.07)
>
>  112 ms (0)
>
>  112 ms (0)
>
>  76 ms (2.07)
>
> 125 s/s
>
>  72 ms (2.53)
>
>
>
>
>
>
>
>
> Without adjustment, the EEG is delayed with respect to real time and to
> event markers that are aligned with real time. This delay does not affect
> timing of events manually entered by the user with respect to the EEG
> during acquisition.
>
> The delay values in the original Advisory Notice were verified with the
> most recent versions of Net Station 4.5 and 5.0, representing the software
> versions that are most widely used by our customer base. The original
> Advisory Notice was issued immediately after this verification effort.
>
> Since releasing the original Advisory Notice on 28 August 2014, we have
> continued our verification testing to confirm these delay values in all
> other versions of Net Station associated with the NA 300 amplifier, in
> order to provide our customers not using Net Station 4.5 or 5.0 with more
> specific guidance.
>
> With the NA 300 amplifier, we found that the filter delay is only present
> in Net Station version 4.4 and later; events are correctly aligned with the
> EEG data when acquired with earlier versions of Net Station (4.3.1 and
> earlier). Furthermore, we found that for data recorded with Net Station
> versions 4.4 through 4.5.7, the correction values for the default 250 s/s
> sampling rate (which is likely used by the majority of customers) is 8 ms.
>
> For data acquired with the NA 400, NA 405 and NA 410 amplifiers, there is
> no modification to the delay values presented in the original Advisory
> Notice.
>
> Starting with Net Station 4.4, all data files contain an amplifier serial
> number. This information can be used to determine whether adjustments are
> required for a given data file acquired with an NA 300 amplifier. Contact
> EGI support for information on how to locate the amplifier serial number
> (if present) in the data file.
>
> EGI will release a tool to adjust the latency delay in affected files in
> the coming weeks. In addition, the Net Station software (version 5.1.2)
> will provide an option for automatic alignment during acquisition.
>
>
> <http://cts.vresp.com/c/?ElectricalGeodesicsI/becac2c8a8/2eeb100ff4/ec13d0112a/utm_content=ascherme%40uvm.edu&utm_source=VerticalResponse&utm_medium=Email&utm_term=&utm_campaign=Update%20to%20Advisory%20Notice%20-%20Anti-Alias%20Filter%20Effects%20on%20EEG%20Timing>Please
> contact EGI support <supportteam at egi.com> for any questions.
>
>
>
>
>
> *From:* eeglablist-bounces at sccn.ucsd.edu [mailto:
> eeglablist-bounces at sccn.ucsd.edu] *On Behalf Of *Makoto Miyakoshi
> *Sent:* Saturday, October 10, 2015 5:53 PM
>
>
> *To:* Isaiah Innis <isainnis at indiana.edu>
> *Cc:* EEGLAB List <eeglablist at sccn.ucsd.edu>
>
> *Subject:* Re: [Eeglablist] Correct for EGI latency error functions
>
>
>
> Dear Isaiah,
>
>
>
> Thank you for sharing this info. I heard of it from Elise, one of visitors
> here. EGI users, please pay attention!
>
>
>
> Makoto
>
>
>
> On Fri, Oct 9, 2015 at 9:48 AM, Isaiah Innis <isainnis at umail.iu.edu>
> wrote:
>
> Hello eeglab list:
>
>
>
> Those of us who use EGI hydro-cel systems received "Advisory Notice:
> Anti-Alias Filter Effects on EEG Timing" warning that there is a fixed
> latency delay present for any event codes sent to the EEG during recording.
> The EEG is delayed with respect to the events, and needs to be corrected by
> either shifting the EEG forward or the events back. While it is possible
> to correct this within NetStation, since our lab analyzes data exclusively
> using eeglab I wrote a series of functions to correct the delay within
> eeglab. It is my hope that others may find this beneficial. However, I am a
> matlab novice and would like to see if anyone on the list has any comments
> or suggestions.
>
>
>
> You can download a .zip archive with the functions here: <
> https://www.dropbox.com/sh/2udz5qrdb79b2b8/AAAS6Bws_O65gJnpnATS1azza?dl=0
> >.
>
>
>
> If you have any questions or criticisms upon reviewing the functions,
> please contact me at: isainnis at indiana.edu
>
> If there is interest, I will make this a plugin for ease of use.
>
>
>
> Thank you,
>
> --
>
> Isaiah Innis
> Indiana University '13
> EEG Technician, IUB IRF
>
>
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>
>
>
>
> --
>
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
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