- Alpha - continuous pan flute
- Alpha High - sounds choir aahs when alpha hits a new relative high
- Alpha Max - sounds high pan flute when total alpha hits a new high for the session
- Alpha minus Beta - continuous surf sound
I find that raw EEG amplitudes have a skewed distribution that makes continuous audio feedback less helpful (too quiet most of the time, and then too loud on the spikes), and to that end I take the square root of the amplitudes to get a somewhat more normal distribution. This transformation provides for a more continuous feel.
When detrending is needed to calculate relative highs, this would normally be done with a threshold object, but I roll my own using percentile objects. This allows me to calculate the threshold based on a longer length of time. In most cases I use the full 2 minutes that the percentile object allows, as opposed to the maximum of 60 seconds that the threshold object uses.
The background is a surf sound which varies according to a 4 second average of total alpha minus total beta. I find that a 4 second average is just long enough to cut through local variation and give a good sense of the underlying trends. The surf sound has been substantially compressed, i.e. the volume variation has been taken out of it, so that the feedback volume ends up being based on actual brainwaves rather than the surf track itself.
That's about it. I include an oscilloscope for both channels, mainly to see that I'm getting good signals. Also a graph of the amplitudes for all major bands, delta, theta, alpha, beta, and gamma, with the session timer set to 6 hours, not sure how useful that is. And there is a trend graph of alpha and the smoothed alpha minus beta on instruments 2, mainly I was using that while getting the design parameters set.
The design will be looking for the surf sound in a Media folder under BioExplorer in a Windows 7 setup. I think even if you set it up right, I believe you will need to go into the Audio Player object, remove it from playlist (will probably be x-d out) and add it back in and you should be good to go.
I think my best recommendation for sites would be P3 & P4. If anyone ends up using this design, I would appreciate your comments. Good luck and bon voyage!