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)