Subject: Re: [AUDITORY] EEG purchase From: Lloyd Smith <lsmith@xxxxxxxx> Date: Tue, 30 Aug 2022 17:16:17 -0400--000000000000cee23e05e77be49d Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi, Hari. As you know, we are uniquely positioned for source estimation because we offer systems with up to 264 channels, but also we develop a leading software platform for source estimation called EMSE Suite, one module of which is designed to interface with a 3D digitizer to measure electrode positions. Other modules perform MR segmentation, head-model specification, coregistration, signal processing, source reconstruction, and visualization. I always encourage people who are interested in source modeling to use our equidistant head-cap layout, which has more coverage on the sides and back of the head. See this link for more information about the equidistant head-cap layout: http://cortechsolutions.com/wp-content/uploads/2022/08/SfN2017_343-2_Equidi= stant_42x68_20171031a.pdf. Also, we can provide a simple tool to facilitate applying flat-type active electrodes in consistent relative positions to the face and neck. Essentially, what I would recommend is a fabric template that can be matched up to the sites on the sides at the border of the head cap and stretched evenly across the cheeks to assist in marking positions for placement of flat-type electrodes. Best regards, Lloyd Smith President Cortech Solutions, Inc. E-mail: LSmith@xxxxxxxx Tel: 910-362-1143 x202 Cell: 910-431-2811 On Tue, Aug 30, 2022 at 12:17 AM Bharadwaj, Hari M <hbharadw@xxxxxxxx> wrote: > Hi All, > > Thank you for sharing the response from Biosemi, Carlos! > > Just wanted to add that we have used the standard ActiveTwo channels (not > the ABR module with high gain) for both ABRs and high-frequency FFRs. Whi= le > we had seen high-frequency spikes in bucket tests, we didn't notice them = in > our FFR frequency plots even at high frequencies. I wonder if this is > simply because in addition to what's noted in Biosemi's response, the > dithering spike amplitudes will also go down with trial averaging when yo= u > have jittered stimulus presentation? > > The trace in Panel C here is an example of what we get with the Biosemi > for (75 dB SPL) 500 Hz pure tones presented in two polarities and then > plotting the. FFT of the summed response (as Amos was describing). A spik= e > at twice that frequency, albeit small, is visible as expected: > https://www.eneuro.org/content/eneuro/9/2/ENEURO.0378-21.2022/F6.large.jp= g > > This is an example of an ABR trace with about 3000 click presentations > (about 90 dB peSPL if I recall correctly) in each of two polarities: > https://www.dropbox.com/s/of9d7od9evv023y/I33_ABR_left_onlineAverage.png?= dl=3D0 > > > Overall, we also have had a very positive experience with Biosemi and wit= h > Cortech in the US. My only comment is that in experiments where source > localization is planned, it may be useful to place some of their external > electrodes on the cheek bones of the face. The broader coverage (EGI nets > have electrodes on the face already) can help disambiguate between certai= n > solutions for the inverse problem > <https://www.sciencedirect.com/science/article/pii/S0165027015003064>. > > > Best, > Hari > ------------------------------ > *From:* AUDITORY - Research in Auditory Perception < > AUDITORY@xxxxxxxx> on behalf of Carlos Benitez-Barrera < > 000001c4037ab8ae-dmarc-request@xxxxxxxx> > *Sent:* Sunday, August 28, 2022 10:50 AM > *To:* AUDITORY@xxxxxxxx <AUDITORY@xxxxxxxx> > *Subject:* Re: [AUDITORY] EEG purchase > > ---- *External Email*: Use caution with attachments, links, or sharing > data ---- > > Dear all, > > > > I wanted to publicly thank everybody for all the responses I received > regarding my upcoming EEG system purchasing. I received very useful > feedback that will help me make an inform decision on which system will b= e > most optimal for my lab. It=E2=80=99s quite obvious from our exchange tha= t every > system has its pros and cons, and it all comes to finding the system that > better suits your needs. I=E2=80=99m still doing my math but I=E2=80=99ll= make a decision > soon. Nevertheless, I learned a lot from this exchange. Kudos to the > Auditory List for being such a useful tool! > > > > Finally, I was contacted by Biosemi regarding the issue that Amos brought > up regarding the dithering process with their system. They provided a > very detail response that they encouraged me to share with all of you. Fo= r > those of you interested on the topic, I=E2=80=99m including their respons= e below. > > > > Thank you again everybody. Best of luck for the new academic year! > > > > Sincerely, > Carlos > > > > *RESPONSE FROM BIOSEMI * > > > > - The spike problem doesn=E2=80=99t play a role with the special ABR chan= nels > because these are amplified an extra factor of 64 before the ADC. So the > spikes are far below the noise level over the full bandwidth. 100Hz to > 3kHz. > > - The spurious tones being discussed in this thread are inherent to > Sigma-Delta ADC converters. > - The phenomenon of sharp spikes at 8 Hz intervals in spectra of long > periods are caused by spurious tones generated in the Sigma-Delta ADCs. > > - All the ADCs in the system show the same behavior. However, the > amplitude of the spikes differ slightly between the channels due to > (internal) ADC tolerances and different electrode offset levels at the > inputs, Therefore, referencing decreases the spikes, but does not elimina= te > them completely (and the effectiveness of referencing differs for differe= nt > channels). > - The spikes are perfectly locked to the sampling frequency, and therefor= e > of nearly infinitely narrow width (see NoiseSpectrumShortedADCzoomed.jpg > attached and at https://imgur.com/a/Y9KVhK0). The spikes are always fixed > at the same frequencies (multiples of 8 Hz). The noise power in the spike= s > is very small. Also note that only FFTs over windows in the order of > hundreds of seconds at the high sample rates show the effect. > - The spurs (spurious tones) have an amplitude of approx. 20 nVrms in the > passband (see NoiseSpectrumShortedADCLin.jpg attached and at the imgur > link). The maximum input signal is 0.5 V peak-to-peak (approx 0.2 Vrms). > This means a SFDR (Spurious Free Dynamic Range) of 140 dB, which is > according to the specs of the ADC. So, our circuitry is able to use the A= DC > to its specs (we do not add or increase spurs). The Sigma-Delta ADCs used > in competing systems have a similar SFDR specs and are likely to show > similar spurious tones. Note that nearly all contemporary EEG system are > based on Sigma-Delta ADCs. > - Besides the spurs at 8 Hz intervals, ActiveTwo shows a perfectly clean > spectrum, see plots of measurements with two EX electrodes in a bowl of > water (NoiseSpectrumElectrodesLin.jpg and NoiseSpectrumElectrodesLog.jpg = -- > FFT of the difference between EX1 and EX2, 1 second FFTs, 0.5 second > overlap, average of 1999 FFTs over a period of 1000 seconds). The small > peaks at 50 and 450 Hz are due to mains interference. > - Competing systems may have a HIGHER noise density at high frequencies > than ActiveTwo (consistent with the choice of a chopper preamp which has > constant noise density, whereas we use a linear preamp with decreasing > noise density at high frequencies). This higher noise may cover the spurs > in those systems. In addition, competing systems may use very high-order > (very steep) FIR decimation filters, whereas we use a 5th order CIC filte= r. > High-order FIR filters may be a bit less susceptible to spurs, but genera= te > a ripple in the passband (we have a flat frequency response) and ringing = on > step input signals (we have no ringing and overshoot). > - For high dynamic range in the time domain, a Sigma-Delta ADC (which we > use in the ActiveTwo) is the best choice. However, for high dynamic range > in the frequency domain it is preferable to use a SAR (Successive > Approximation Register) type ADC, which we use in the hypersampling versi= on > of ActiveTwo, see > https://www.neurospec.com/Products/Details/1076/activetwo---hyper-samplin= g-edition > - The whole spurious tones issue only plays a role with input signals on > standard active electrode channels (not ABR channels) above 1kHz, because > below 1 kHz the spurious tones are below the amplifier noise. > > > > *From: *AUDITORY - Research in Auditory Perception < > AUDITORY@xxxxxxxx> on behalf of Ravinderjit Singh < > singh415@xxxxxxxx> > *Reply-To: *Ravinderjit Singh <singh415@xxxxxxxx> > *Date: *Monday, August 22, 2022 at 11:21 PM > *To: *"AUDITORY@xxxxxxxx" <AUDITORY@xxxxxxxx> > *Subject: *Re: EEG purchase > > > > Hello all, > > > > Curious if anyone has any experience in comparing the OpenBCI products > (Like the Mark IV <https://shop.openbci.com/products/ultracortex-mark-iv>= ) > compared to the Biosemi Active Two system. Curious what the difference > between the two products would be for cortical measures. Currently the > OpenBCI products cannot sample as fast as Biosemi, but OpenBCI is fast > enough for cortical measures. I prefer the price point and openness of > OpenBCI =F0=9F=99=82 > > > > Best, > > Rav > > > > > -------------------------------------------------------------------------= ---------- > > Ravinderjit Singh, PhD > > MD/PhD Student > > Purdue University - Weldon School of Biomedical EngMark IVineering > > Indiana University - School of Medicine=E2=80=8B > ------------------------------ > > *From:* AUDITORY - Research in Auditory Perception < > AUDITORY@xxxxxxxx> on behalf of Kaganovich, Natalya B < > kaganovi@xxxxxxxx> > *Sent:* Friday, August 19, 2022 10:38 AM > *To:* AUDITORY@xxxxxxxx <AUDITORY@xxxxxxxx> > *Subject:* Re: [AUDITORY] EEG purchase > > > > Hello Carlos, > > > > I have been using the Biosemi Active Two system with children ages 7-14 o= r > so and with adults for about 10 years. I love it. I only have 32 > electrodes, which was an intentional choice. I find the application quite > fast and easy =E2=80=93 to speed up the process, we use 2 people to apply= gel into > electrode holders and to plug in electrodes. It takes about 12-15 minutes > start to finish. I worked with Neuroscan during the post-doc. It may have > changed by now, but the data quality with Biosemi is amazing compared to > Neuroscan. Lloyd Smith and his team at CortechSolutions (the Biosemi > distributor in the US) have been extremely supportive and respond promptl= y. > Whenever we need to repair electrodes, we get them back within a week or > so. Lloyd is extremely knowledgeable and was able to guide us through > unexpected issues when the did arise. > > > > I will mention a couple of things to consider: > > 1. The wires are rather delicate. I believe the later version of > electrode sets have the connection between the wire and the electrode > strengthened. We do have both graduate and undergraduate students usin= g the > electrodes but provide extensive training on handling. We only had a f= ew > breakages. > 2. Biosemi does not have in-house data processing software. This may > or may not be an issue for you =E2=80=93 many labs now use Matlab-base= d programs > for data analysis. I use EMSE, which is now also owned by CortechSolut= ions. > > Good luck with your lab set up! > > > > Natalya > > > > Natalya Kaganovich, PhD > > Associate Professor > > Department of Speech, Language, and Hearing Sciences > > Department of Psychological Sciences > > Purdue University > > kaganovi@xxxxxxxx > > (765)494-4233 > > > > > > > > *From:* AUDITORY - Research in Auditory Perception < > AUDITORY@xxxxxxxx> *On Behalf Of *Carlos Benitez-Barrera > *Sent:* Friday, August 12, 2022 11:21 AM > *To:* AUDITORY@xxxxxxxx > *Subject:* EEG purchase > > > > ---- *External Email*: Use caution with attachments, links, or sharing > data ---- > > > > Dear Auditory List, > > > > I am planning on purchasing an EEG system for my new lab at UW-Madison, > USA. I have been in contact with several EEG providers, and I=E2=80=99m s= till > undecisive on which system would be best for my lab. I=E2=80=99m familiar= with > Neuroscan and EGI, but I=E2=80=99m actually leaning towards Biosemi or Br= ain > Products (Brain and Vision in the US). I run simple auditory paradigms wi= th > children (ages 3 to 14) and adults. The main characteristics that I=E2=80= =99m > looking for are (not necessarily in order): > > - Ease of use > - Prep cap time (important to minimize with children) > - Customer support > - Signal quality > > > > I=E2=80=99m shooting for a 64-channel system. Also, I=E2=80=99m still hes= itating between > saline caps or gel caps. I heard that the Biosemi caps despite of being g= el > based are very fast to get going. > > > > Anyway, I=E2=80=99m just looking for some advice from any of you working = with > these systems. Any experiences or recommendations will help! > > > > Thank you in advance for your taking your time to reply! > > > > Sincerely, > > Carlos > > > > > > > --=20 Cortech Solutions, Inc.1409 Audubon Blvd, Suite B1 Wilmington, NC 28403 USA Tel: 910-362-1143 Fax: 910-378-3443 Sales: sales@xxxxxxxx=20 <mailto:sales@xxxxxxxx> Support / repairs:=20 support@xxxxxxxx <mailto:support@xxxxxxxx> Billing=20 / administration: admin@xxxxxxxx=20 <mailto:admin@xxxxxxxx> Web: www.cortechsolutions.com=20 <http://www.cortechsolutions.com> --000000000000cee23e05e77be49d Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr">Hi, Hari. As you know, we are uniquely positioned for sour= ce estimation because we offer systems with=C2=A0up to 264 channels, but al= so we develop a leading software platform for source estimation called EMSE= Suite, one module of which is designed to interface with a 3D digitizer to= measure electrode positions. Other modules perform MR segmentation, head-m= odel specification, coregistration, signal processing, source reconstructio= n, and visualization.=C2=A0<div><br></div><div>I always encourage people wh= o are interested in source modeling to use our equidistant=C2=A0head-cap la= yout, which has more coverage on the sides and back of the head.=C2=A0 See = this link for more information about the equidistant head-cap layout: <a hr= ef=3D"http://cortechsolutions.com/wp-content/uploads/2022/08/SfN2017_343-2_= Equidistant_42x68_20171031a.pdf">http://cortechsolutions.com/wp-content/upl= oads/2022/08/SfN2017_343-2_Equidistant_42x68_20171031a.pdf</a>. Also, we ca= n provide a simple tool to facilitate applying flat-type active electrodes = in consistent relative positions to the face and neck. Essentially, what I = would recommend is a fabric template that can be matched up to the sites on= the sides at the border of the head cap and stretched evenly across the ch= eeks to assist in marking positions for placement of flat-type electrodes.= =C2=A0 =C2=A0=C2=A0<div><br clear=3D"all"><div><div dir=3D"ltr" class=3D"gm= ail_signature" data-smartmail=3D"gmail_signature">Best regards, <br><br>Llo= yd Smith <br>President <br>Cortech Solutions, Inc. <br><br><div>E-mail: <a = href=3D"mailto:LSmith@xxxxxxxx" target=3D"_blank">LSmith@xxxxxxxx= hsolutions.com</a>=C2=A0<br><div>Tel: 910-362-1143 x202=C2=A0<div>Cell: 910= -431-2811<br></div></div><div><br><div><div><br></div></div></div></div></d= iv></div><br></div></div></div><br><div class=3D"gmail_quote"><div dir=3D"l= tr" class=3D"gmail_attr">On Tue, Aug 30, 2022 at 12:17 AM Bharadwaj, Hari M= <<a href=3D"mailto:hbharadw@xxxxxxxx">hbharadw@xxxxxxxx</a>> wro= te:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px = 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class= =3D"gmail-msg-6155536384896132741"> <div dir=3D"ltr"> <div style=3D"font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt= ;color:rgb(0,0,0);background-color:rgb(255,255,255)"> <span style=3D"font-size:12pt;margin:0px;color:black;background-color:white= ">Hi All,</span><span style=3D"color:rgb(0,0,0);background-color:rgb(255,25= 5,255);display:inline"></span></div> <div style=3D"font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt= ;color:rgb(0,0,0);background-color:rgb(255,255,255)"> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > Thank you for sharing the response from Biosemi, Carlos!=C2=A0</div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > Just wanted to add that we have used the standard ActiveTwo channels (not t= he ABR module with high gain) for both ABRs and high-frequency FFRs. While = we had seen high-frequency spikes in bucket tests, we didn't notice the= m in our FFR frequency plots even at high frequencies. I wonder if this is simply because=C2=A0<span style=3D"m= argin:0px">in addition to what's noted in Biosemi's response, the d= ithering spike amplitudes will also go down with trial averaging when you h= ave jittered stimulus presentation?</span></div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > The trace in Panel C here is an example of what we get with the Biosemi for= (75 dB SPL) 500 Hz pure tones presented in two polarities and then plottin= g the. FFT of the summed response (as Amos was describing). A spike at twic= e that frequency, albeit small, is visible as expected:=C2=A0=C2=A0<a href=3D"https://www.eneuro.org/conte= nt/eneuro/9/2/ENEURO.0378-21.2022/F6.large.jpg" rel=3D"noopener noreferrer"= style=3D"margin:0px" target=3D"_blank">https://www.eneuro.org/content/eneu= ro/9/2/ENEURO.0378-21.2022/F6.large.jpg</a></div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > This is an example of an ABR trace with about 3000 click presentations (abo= ut 90 dB peSPL if I recall correctly) in each of two polarities:=C2=A0=C2= =A0<a href=3D"https://www.dropbox.com/s/of9d7od9evv023y/I33_ABR_left_online= Average.png?dl=3D0" rel=3D"noopener noreferrer" style=3D"margin:0px" target= =3D"_blank">https://www.dropbox.com/s/of9d7od9evv023y/I33_ABR_left_onlineAv= erage.png?dl=3D0</a></div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > Overall, we also have had a very positive experience with Biosemi and with = Cortech in the US. My only comment is that in experiments where source loca= lization is planned, it may be useful to place some of their external elect= rodes on the cheek bones of the face.<span style=3D"margin:0px">=C2=A0</span><a href=3D"https://www.scienc= edirect.com/science/article/pii/S0165027015003064" rel=3D"noopener noreferr= er" title=3D"https://www.sciencedirect.com/science/article/pii/S01650270150= 03064" style=3D"margin:0px" target=3D"_blank">The broader coverage (EGI nets have electrodes on the face already) can help d= isambiguate between certain solutions for the inverse problem</a>.</div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > <br> </div> <div style=3D"font-size:12pt;margin:0px;color:black;background-color:white"= > Best,</div> <span style=3D"font-size:12pt;margin:0px;color:black;background-color:white= ">Hari</span><br> </div> <div id=3D"gmail-m_-6155536384896132741appendonsend"></div> <hr style=3D"display:inline-block;width:98%"> <div id=3D"gmail-m_-6155536384896132741divRplyFwdMsg" dir=3D"ltr"><font fac= e=3D"Calibri, sans-serif" style=3D"font-size:11pt" color=3D"#000000"><b>Fro= m:</b> AUDITORY - Research in Auditory Perception <<a href=3D"mailto:AUD= ITORY@xxxxxxxx" target=3D"_blank">AUDITORY@xxxxxxxx</a>> o= n behalf of Carlos Benitez-Barrera <<a href=3D"mailto:000001c4037ab8ae-d= marc-request@xxxxxxxx" target=3D"_blank">000001c4037ab8ae-dmarc-requ= est@xxxxxxxx</a>><br> <b>Sent:</b> Sunday, August 28, 2022 10:50 AM<br> <b>To:</b> <a href=3D"mailto:AUDITORY@xxxxxxxx" target=3D"_blank">AU= DITORY@xxxxxxxx</a> <<a href=3D"mailto:AUDITORY@xxxxxxxx" = target=3D"_blank">AUDITORY@xxxxxxxx</a>><br> <b>Subject:</b> Re: [AUDITORY] EEG purchase</font> <div>=C2=A0</div> </div> <div lang=3D"EN-US"> <table style=3D"background-color:rgb(255,240,160);font-size:10pt;font-famil= y:Verdana;color:rgb(0,0,0);text-align:left;width:100%"> <tbody> <tr> <td style=3D"padding:5px">---- <b>External Email</b>: Use caution with atta= chments, links, or sharing data ----</td> </tr> </tbody> </table> <br> <div> <div> <p>Dear all,</p> <p>=C2=A0</p> <p>I wanted to publicly thank everybody for all the responses I received re= garding my upcoming EEG system purchasing. I received very useful feedback = that will help me make an inform decision on which system will be most opti= mal for my lab. It=E2=80=99s quite obvious from our exchange that every system has its pro= s and cons, and it all comes to finding the system that better suits your n= eeds. I=E2=80=99m still doing my math but I=E2=80=99ll make a decision soon= . Nevertheless, I learned a lot from this exchange. Kudos to the Auditory List for being such a useful tool!</p> <p>=C2=A0</p> <p>Finally, I was contacted by Biosemi regarding the issue that Amos brough= t up regarding the <span style=3D"font-size:11.5pt;color:black">dithering process with their s= ystem. They provided a very detail response that they encouraged me to shar= e with all of you. For those of you interested on the topic, I=E2=80=99m in= cluding their response below. </span></p> <p>=C2=A0</p> <p>Thank you again everybody. Best of luck for the new academic year!</p> <p>=C2=A0</p> <p>Sincerely,<br> Carlos</p> <p>=C2=A0</p> <p><b>RESPONSE FROM BIOSEMI </b></p> <p><b>=C2=A0</b></p> <p style=3D"margin-left:4.8pt"><span style=3D"color:black">- The spike prob= lem doesn=E2=80=99t play a role with the special ABR channels because these= are amplified an extra factor of 64 before the ADC. So the spikes are far = below the noise level over the full bandwidth. 100Hz to 3kHz.=C2=A0</span></p> <p style=3D"margin-left:4.8pt"><span style=3D"color:black">- The spurious t= ones being discussed in this thread are inherent to Sigma-Delta ADC convert= ers.<br> - The phenomenon of sharp spikes at 8 Hz intervals in spectra of long perio= ds are caused by spurious tones generated in the Sigma-Delta ADCs.</span></= p> <p style=3D"margin-left:4.8pt"><span style=3D"color:black">- All the ADCs i= n the system show the same behavior. However, the amplitude of the spikes d= iffer slightly between the channels due to (internal) ADC tolerances and di= fferent electrode offset levels at the inputs, Therefore, referencing decreases the spikes, = but does not eliminate them completely (and the effectiveness of referencin= g differs for different channels).<br> - The spikes are perfectly locked to the sampling frequency, and therefore = of nearly infinitely narrow width (see NoiseSpectrumShortedADCzoomed.jpg at= tached and at=C2=A0<a href=3D"https://imgur.com/a/Y9KVhK0" target=3D"_blank= ">https://imgur.com/a/Y9KVhK0</a>). The spikes are always fixed at the same frequencies (multiples of 8 Hz). The noise power in the = spikes is very small. Also note that only FFTs over windows in the order of= hundreds of seconds at the high sample rates show the effect.<br> - The spurs (spurious tones) have an amplitude of approx. 20 nVrms in the p= assband (see NoiseSpectrumShortedADCLin.jpg attached and at the imgur link)= . The maximum input signal is 0.5 V peak-to-peak (approx 0.2 Vrms). This me= ans a SFDR (Spurious Free Dynamic Range) of 140 dB, which is according to the specs of the ADC. So, our circ= uitry is able to use the ADC to its specs (we do not add or increase spurs)= . The Sigma-Delta ADCs used in competing systems have a similar SFDR specs = and are likely to show similar spurious tones. Note that nearly all contemporary EEG system are based on Sigma-Del= ta ADCs.<br> - Besides the spurs at 8 Hz intervals, ActiveTwo shows a perfectly clean sp= ectrum, see plots of measurements with two EX electrodes in a bowl of water= (NoiseSpectrumElectrodesLin.jpg and NoiseSpectrumElectrodesLog.jpg -- FFT = of the difference between EX1 and EX2, 1 second FFTs, 0.5 second overlap, average of 1999 FFTs over a period= of 1000 seconds). The small peaks at 50 and 450 Hz are due to mains interf= erence.<br> - Competing systems may have a HIGHER noise density at high frequencies tha= n ActiveTwo (consistent with the choice of a chopper preamp which has const= ant noise density, whereas we use a linear preamp with decreasing noise den= sity at high frequencies). This higher noise may cover the spurs in those systems. In addition, competing = systems may use very high-order (very steep) FIR decimation filters, wherea= s we use a 5th order CIC filter. High-order FIR filters may be a bit less s= usceptible to spurs, but generate a ripple in the passband (we have a flat frequency response) and ringing o= n step input signals (we have no ringing and overshoot).<br> - For high dynamic range in the time domain, a Sigma-Delta ADC (which we us= e in the ActiveTwo) is the best choice. However, for high dynamic range in = the frequency domain it is preferable to use a SAR (Successive Approximatio= n Register) type ADC, which we use in the hypersampling version of ActiveTwo, see=C2=A0<a href=3D"https://www= .neurospec.com/Products/Details/1076/activetwo---hyper-sampling-edition" ta= rget=3D"_blank">https://www.neurospec.com/Products/Details/1076/activetwo--= -hyper-sampling-edition</a><br> - The whole spurious tones issue only plays a role with input signals on st= andard active electrode channels (not ABR channels) above 1kHz, because bel= ow 1 kHz the spurious tones are below the amplifier noise.<br> <br> </span></p> <p>=C2=A0</p> <div style=3D"border-right:none;border-bottom:none;border-left:none;border-= top:1pt solid rgb(181,196,223);padding:3pt 0in 0in"> <p><b><span style=3D"font-size:12pt;color:black">From: </span> </b><span style=3D"font-size:12pt;color:black">AUDITORY - Research in Audit= ory Perception <<a href=3D"mailto:AUDITORY@xxxxxxxx" target=3D"_b= lank">AUDITORY@xxxxxxxx</a>> on behalf of Ravinderjit Singh <<= a href=3D"mailto:singh415@xxxxxxxx" target=3D"_blank">singh415@xxxxxxxx= </a>><br> <b>Reply-To: </b>Ravinderjit Singh <<a href=3D"mailto:singh415@xxxxxxxx= U" target=3D"_blank">singh415@xxxxxxxx</a>><br> <b>Date: </b>Monday, August 22, 2022 at 11:21 PM<br> <b>To: </b>"<a href=3D"mailto:AUDITORY@xxxxxxxx" target=3D"_bla= nk">AUDITORY@xxxxxxxx</a>" <<a href=3D"mailto:AUDITORY@xxxxxxxx= .MCGILL.CA" target=3D"_blank">AUDITORY@xxxxxxxx</a>><br> <b>Subject: </b>Re: EEG purchase</span></p> </div> <div> <p>=C2=A0</p> </div> <div> <p style=3D"background:white"><span style=3D"font-size:12pt;color:black">He= llo all,</span></p> </div> <div> <p style=3D"background:white"><span style=3D"font-size:12pt;color:black">= =C2=A0</span></p> </div> <div> <p style=3D"background:white"><span style=3D"font-size:12pt;color:black">Cu= rious if anyone has any experience in comparing the OpenBCI products (Like = the <a href=3D"https://shop.openbci.com/products/ultracortex-mark-iv" title=3D"= https://shop.openbci.com/products/ultracortex-mark-iv" target=3D"_blank"> Mark IV</a>) compared to the Biosemi Active Two system. Curious what the di= fference between the two products would be for cortical measures. Currently= the OpenBCI products cannot sample as fast as Biosemi, but OpenBCI is fast= enough for cortical measures. I prefer the price point and openness of OpenBCI </span><span style=3D"font-= size:12pt;font-family:"Apple Color Emoji";color:black">=F0=9F=99= =82</span><span style=3D"font-size:12pt;color:black"></span></p> </div> <div> <p style=3D"background:white"><span style=3D"font-size:12pt;color:black">= =C2=A0</span></p> </div> <div> <p style=3D"background:white"><span style=3D"font-size:12pt;color:black">Be= st,</span></p> </div> <div> <p style=3D"background:white"><span style=3D"font-size:12pt;color:black">Ra= v</span></p> </div> <div> <div> <p><span style=3D"font-size:12pt;color:black">=C2=A0</span></p> </div> <div id=3D"gmail-m_-6155536384896132741x_Signature"> <div> <div> <p><span style=3D"color:black">--------------------------------------------= ---------------------------------------</span><span style=3D"font-size:12pt= ;color:black"></span></p> </div> <div> <p><span style=3D"color:black">Ravinderjit Singh, PhD</span><span style=3D"= font-size:12pt;color:black"></span></p> </div> <div> <p><span style=3D"color:black">MD/PhD Student</span><span style=3D"font-siz= e:12pt;color:black"></span></p> </div> <div> <p><span style=3D"color:black">Purdue University - Weldon School of Biomedi= cal EngMark IVineering=C2=A0=C2=A0</span><span style=3D"font-size:12pt;colo= r:black"></span></p> </div> <div> <p><span style=3D"color:black">Indiana University - School of Medicine=E2= =80=8B</span><span style=3D"font-size:12pt;color:black"></span></p> </div> </div> </div> </div> <div align=3D"center" style=3D"text-align:center"> <hr size=3D"2" width=3D"98%" align=3D"center"> </div> <div id=3D"gmail-m_-6155536384896132741x_divRplyFwdMsg"> <p><b><span style=3D"color:black">From:</span></b><span style=3D"color:blac= k"> AUDITORY - Research in Auditory Perception <<a href=3D"mailto:AUDITO= RY@xxxxxxxx" target=3D"_blank">AUDITORY@xxxxxxxx</a>> on b= ehalf of Kaganovich, Natalya B <<a href=3D"mailto:kaganovi@xxxxxxxx" t= arget=3D"_blank">kaganovi@xxxxxxxx</a>><br> <b>Sent:</b> Friday, August 19, 2022 10:38 AM<br> <b>To:</b> <a href=3D"mailto:AUDITORY@xxxxxxxx" target=3D"_blank">AU= DITORY@xxxxxxxx</a> <<a href=3D"mailto:AUDITORY@xxxxxxxx" = target=3D"_blank">AUDITORY@xxxxxxxx</a>><br> <b>Subject:</b> Re: [AUDITORY] EEG purchase</span> </p> <div> <p>=C2=A0</p> </div> </div> <div> <div> <p><span style=3D"font-size:11pt">Hello Carlos,</span></p> <p><span style=3D"font-size:11pt">=C2=A0</span></p> <p><span style=3D"font-size:11pt">I have been using the Biosemi Active Two = system with children ages 7-14 or so and with adults for about 10 years. I = love it. I only have 32 electrodes, which was an intentional choice. I find= the application quite fast and easy =E2=80=93 to speed up the process, we use 2 people to = apply gel into electrode holders and to plug in electrodes. It takes about = 12-15 minutes start to finish. I worked with Neuroscan during the post-doc.= It may have changed by now, but the data quality with Biosemi is amazing compared to Neuroscan. Lloyd Smith and his= team at CortechSolutions (the Biosemi distributor in the US) have been ext= remely supportive and respond promptly. Whenever we need to repair electrod= es, we get them back within a week or so. Lloyd is extremely knowledgeable and was able to guide us through u= nexpected issues when the did arise. </span></p> <p><span style=3D"font-size:11pt">=C2=A0</span></p> <p><span style=3D"font-size:11pt">I will mention a couple of things to cons= ider: </span></p> <ol start=3D"1" type=3D"1"> <li>The wires are rather delicate. I believe the later version of electrode= sets have the connection between the wire and the electrode strengthened. = We do have both graduate and undergraduate students using the electrodes but provide extensive training on handling. We only had a few breakages. <= /li><li>Biosemi does not have in-house data processing software. This may o= r may not be an issue for you =E2=80=93 many labs now use Matlab-based prog= rams for data analysis. I use EMSE, which is now also owned by CortechSolut= ions. </li></ol> <p>Good luck with your lab set up!</p> <p>=C2=A0</p> <p>Natalya</p> <p><span style=3D"font-size:11pt">=C2=A0</span></p> <p><span style=3D"font-size:11pt">Natalya Kaganovich, PhD</span></p> <p><span style=3D"font-size:11pt">Associate Professor</span></p> <p><span style=3D"font-size:11pt">Department of Speech, Language, and Heari= ng Sciences</span></p> <p><span style=3D"font-size:11pt">Department of Psychological Sciences</spa= n></p> <p><span style=3D"font-size:11pt">Purdue University</span></p> <p><span style=3D"font-size:11pt"><a href=3D"mailto:kaganovi@xxxxxxxx" ta= rget=3D"_blank"><span style=3D"color:rgb(5,99,193)">kaganovi@xxxxxxxx</sp= an></a></span></p> <p><span style=3D"font-size:11pt">(765)494-4233</span></p> <p><span style=3D"font-size:11pt">=C2=A0</span></p> <p>=C2=A0</p> <p><span style=3D"font-size:11pt">=C2=A0</span></p> <div> <div style=3D"border-right:none;border-bottom:none;border-left:none;border-= top:1pt solid rgb(225,225,225);padding:3pt 0in 0in"> <p><b><span style=3D"font-size:11pt">From:</span></b><span style=3D"font-si= ze:11pt"> AUDITORY - Research in Auditory Perception <<a href=3D"mailto:= AUDITORY@xxxxxxxx" target=3D"_blank">AUDITORY@xxxxxxxx</a>>= ; <b>On Behalf Of </b>Carlos Benitez-Barrera<br> <b>Sent:</b> Friday, August 12, 2022 11:21 AM<br> <b>To:</b> <a href=3D"mailto:AUDITORY@xxxxxxxx" target=3D"_blank">AU= DITORY@xxxxxxxx</a><br> <b>Subject:</b> EEG purchase</span></p> </div> </div> <p>=C2=A0</p> <table border=3D"0" cellpadding=3D"0" width=3D"100%" style=3D"width:100%;ba= ckground:rgb(255,240,160)"> <tbody> <tr> <td style=3D"padding:3.75pt"> <p><span style=3D"font-size:10pt;font-family:Verdana,sans-serif;color:black= ">---- <b>External Email</b>: Use caution with attachments, links, or sharing data= ----</span></p> </td> </tr> </tbody> </table> <p><span style=3D"font-size:11pt">=C2=A0</span></p> <div> <p><span style=3D"font-size:11pt;color:black">Dear Auditory List,</span></p= > <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">I am planning on purchasing a= n EEG system for my new lab at UW-Madison, USA. I have been in contact with= several EEG providers, and I=E2=80=99m still undecisive on which system wo= uld be best for my lab. I=E2=80=99m familiar with Neuroscan and EGI, but I=E2=80=99m actually= leaning towards Biosemi or Brain Products (Brain and Vision in the US). I = run simple auditory paradigms with children (ages 3 to 14) and adults. The = main characteristics that I=E2=80=99m looking for are (not necessarily in order):</span></p> <ul type=3D"disc" style=3D"margin-top:0in"> <li style=3D"color:black"><span style=3D"font-size:11pt">Ease of use</span>= </li><li style=3D"color:black"><span style=3D"font-size:11pt">Prep cap time= (important to minimize with children)</span></li><li style=3D"color:black"= ><span style=3D"font-size:11pt">Customer support</span></li><li style=3D"co= lor:black"><span style=3D"font-size:11pt">Signal quality</span></li></ul> <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">I=E2=80=99m shooting for a 64= -channel system. Also, I=E2=80=99m still hesitating between saline caps or = gel caps. I heard that the Biosemi caps despite of being gel based are very= fast to get going.=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">Anyway, I=E2=80=99m just look= ing for some advice from any of you working with these systems. Any experie= nces or recommendations will help!</span></p> <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">Thank you in advance for your= taking your time to reply!</span></p> <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">Sincerely,</span></p> <p><span style=3D"font-size:11pt;color:black">Carlos</span></p> <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt;color:black">=C2=A0</span></p> <p><span style=3D"font-size:11pt">=C2=A0</span></p> </div> </div> </div> </div> </div> </div> </div> </div></blockquote></div> <br> <hr><font size=3D"2">Cortech Solutions, Inc.</font><div><font size=3D"2">14= 09 Audubon Blvd, Suite B1</font></div><div><font size=3D"2">Wilmington, NC = 28403 USA</font></div><div><font size=3D"2"><br></font></div><div><font siz= e=3D"2">Tel: 910-362-1143</font></div><div><font size=3D"2">Fax:</font> 910= -378-3443<br></div><div><font size=3D"2"><br></font></div><div><font size= =3D"2">Sales: <a href=3D"mailto:sales@xxxxxxxx" target=3D"_blan= k">sales@xxxxxxxx</a></font></div><div><font size=3D"2">Support= / repairs: <a href=3D"mailto:support@xxxxxxxx" target=3D"_blan= k">support@xxxxxxxx</a></font></div><div><font size=3D"2">Billi= ng / administration: <a href=3D"mailto:admin@xxxxxxxx" target= =3D"_blank">admin@xxxxxxxx</a></font></div><div><font size=3D"2= "><br></font></div><div><div><font size=3D"2">Web: <a href=3D"http://www.co= rtechsolutions.com" target=3D"_blank">www.cortechsolutions.com</a></font></= div></div><div style=3D"font-size:1.3em"><br></div> --000000000000cee23e05e77be49d--