Active Two Questions (CM. ABR, etc.)

[ctownsend]

I recently bought a used Active Two system. It came with various electrodes but some of them I'm not sure what they are for. The front panel of the A/D box has CMS/DRL in the first slot as is typical but in the second slot it has something labeled "LA RA LL" (and I have corresponding electrodes with the same labels). What does that mean? Is it for doing ABRs? The photos I see of ABR electrodes are similar but have "Ref" electrode instead of "LL".

Here's a photo:https://photos.app.goo.gl/8VovU6Gai5PX5vAx6

Also, I'm interested in recording the cochlear microphonic (as well as maybe ABR and EEG). My understanding is to do that I need to use an alternating stimulus and then when summing the sweeps the condensation sweeps need to be subtracted from the rarefaction sweeps. How do you do that in ActiView?

And I'd like to set up a trigger based on the stimulus. Is it possible to hook up a soundcard output into one of the (parallel port) trigger inputs and have that activate the trigger? 

In the ActiView ABR tab I don't see any trigger options although I do in the ERP tab. For what I want to do should I use the ABR tab or the ERP tab?

[Coen]

It is a custom made system for 16+3 channel ECG (LA RA LL is the Wilson Central Terminal). It is probably something like 20 years old. Please email the serial number to info@biosemi.com, and I can check which upgrades are still possible.

Soundcard to trigger interface can be done with the ERGO-OPTICAL see https://www.youtube.com/watch?v=_OMoXttIguc

Best regards, Coen (BioSemi)

[ctownsend]

Thanks. I will send an email. Also, is it possible to connect a sound card output directly to trigger pin1 on the 37-pin parallel port? Does the voltage need to be held high or can is it enough to just pulse? And how much measurement jitter and latency is there from when the trigger goes high? Is the trigger sampled at the overall samplerate of the measurements so the jitter will be about 1 sample?

[Coen]

The trigger port needs TTL level signals. In order to connect an audio line signal, you will need to convert to TTL with a comparator and flip-flop. The accuracy of trigger timing is one sample length, see https://www.biosemi.com/faq/review_trigger_timing.htm

Best regards, Coen

[ctownsend]

Thanks again. The audio interface I have has DC-coupled outputs so I should be able to directly drive 5V DC. I'll probably add a current limiting resistor to be on the safe side.