Hello, I was wondering if anyone could tell me the difference in frequency response (or other characteristics) of the special ABR electrodes compared to the normal active electrodes?
Has anyone been able to do a comparison between the two, preferably in the same testing session?
Thanks!
frequency response of ABR vs normal active electrodes
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Coen
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Re: frequency response of ABR vs normal active electrodes
Specs for the special ABR active electrodes are:
- bandwidth 100 Hz to 3 kHz (16 kHz sample rate)
- AC input range 8 mVpp (AC amplification)
- DC input range ± 250 mV
- noise over the the full bandwidth less than 4 uV pp
- CMRR > 150 dB
- LSB = 488 picoVolt
Noise is a factor of 3 lower, and CMRR is 50 dB higher than with our standard active electrodes.
Highpass cutoff can be lowered from 100Hz to 10 Hz with offline equalizing
The special ABR setup is only available as a 2 channel (Left and Right versus Reference) setup, whereas the standard active electrodes can be used on 16 kHz with up to 32+8 electrodes (or even 128+8 with HighSpeed firmware). In the ABR setup, the difference between a pair of electrodes is digitized after (high gain) AC amplification, whereas with the standard electrodes the voltage with respect to CMS is digitized after (low gain) DC amplification (and the difference between channels is calculated in software).
Both setups are being successfully used to record ABR by our customers. In theory, the special ABR electrodes are superior for high frequency measurements (lower high frequency noise, better CMRR). However, it is still unclear whether this has practical advantages, since it may well be that the noise level of the electrode-skin interface is the limiting factor in most situations (we are still waiting on firm customer feedback on this issue). Also see viewtopic.php?f=1&t=591&hilit=abr (standard electrodes) versus viewtopic.php?f=4&t=596&p=1813&hilit=abr#p1813(special ABR electrodes)
Best regards, Coen (BioSemi)
- bandwidth 100 Hz to 3 kHz (16 kHz sample rate)
- AC input range 8 mVpp (AC amplification)
- DC input range ± 250 mV
- noise over the the full bandwidth less than 4 uV pp
- CMRR > 150 dB
- LSB = 488 picoVolt
Noise is a factor of 3 lower, and CMRR is 50 dB higher than with our standard active electrodes.
Highpass cutoff can be lowered from 100Hz to 10 Hz with offline equalizing
The special ABR setup is only available as a 2 channel (Left and Right versus Reference) setup, whereas the standard active electrodes can be used on 16 kHz with up to 32+8 electrodes (or even 128+8 with HighSpeed firmware). In the ABR setup, the difference between a pair of electrodes is digitized after (high gain) AC amplification, whereas with the standard electrodes the voltage with respect to CMS is digitized after (low gain) DC amplification (and the difference between channels is calculated in software).
Both setups are being successfully used to record ABR by our customers. In theory, the special ABR electrodes are superior for high frequency measurements (lower high frequency noise, better CMRR). However, it is still unclear whether this has practical advantages, since it may well be that the noise level of the electrode-skin interface is the limiting factor in most situations (we are still waiting on firm customer feedback on this issue). Also see viewtopic.php?f=1&t=591&hilit=abr (standard electrodes) versus viewtopic.php?f=4&t=596&p=1813&hilit=abr#p1813(special ABR electrodes)
Best regards, Coen (BioSemi)
Re: frequency response of ABR vs normal active electrodes
Great, thanks for that detailed information Coen! Do you have similar information (gain and frequency response) for the standard active electrodes too?
IE, is there any attenuation of high frequencies below the 'bandwidth' figure that Acti-View quotes for each given sampling rate? For 16 KHz this is around 3 KHz, but is the frequency response of the active electrodes really flat to 3 KHz?
I've been using the standard electrodes for frequency-following responses. I have OK responses, but sometimes have difficulty getting good SNR's without large numbers of trials. I'm not quite sure how to test whether the ABR setup would help. Has Bio-Semi or anyone else done any comparisons (data collection) using the two systems in the same session and subject that you know of?
I'd do it, but I don't have the ABR setup...
IE, is there any attenuation of high frequencies below the 'bandwidth' figure that Acti-View quotes for each given sampling rate? For 16 KHz this is around 3 KHz, but is the frequency response of the active electrodes really flat to 3 KHz?
I've been using the standard electrodes for frequency-following responses. I have OK responses, but sometimes have difficulty getting good SNR's without large numbers of trials. I'm not quite sure how to test whether the ABR setup would help. Has Bio-Semi or anyone else done any comparisons (data collection) using the two systems in the same session and subject that you know of?
I'd do it, but I don't have the ABR setup...
-
Coen
- Site Admin
- Posts: 1125
- Joined: Fri Mar 26, 2004 7:00 pm
- Location: Amsterdam, Netherlands
- Contact:
Re: frequency response of ABR vs normal active electrodes
Both the standard and ABR electrodes have a low-pass response as described in http://www.biosemi.com/faq/adjust_filter.htm.
The standard electrodes are DC, the ABR electrodes are AC with a first order high-pass with -3dB point at 100 Hz.
LSB for standard electrodes is 31.25 nV (1/32th uV), LSB for the ABR electrodes is 488 pV (1/2048th uV)
Best regards, Coen (BioSemi)
The standard electrodes are DC, the ABR electrodes are AC with a first order high-pass with -3dB point at 100 Hz.
LSB for standard electrodes is 31.25 nV (1/32th uV), LSB for the ABR electrodes is 488 pV (1/2048th uV)
Best regards, Coen (BioSemi)