Baseline Smoothing
From Unofficial BOINC Wiki
[edit] General
The Arecibo Radio Telescope has the ability to detect and capture radio signals over a very wide frequency range, this means of course that it detects radio waves with all kinds of Bandwidths. Narrowband Signals are what we believe an alien civilization would use to communicate, whereas Broadband events are most likely due to natural astronomical processes. (It takes a tremendous amount of energy to send a Broadband Signal.) Hence, SETI@Home is interested in focusing on the Narrow Bandwidth signals (though it investigates Broadband Signals as well). In the plot to the left you can see that over the defined interval we have energy across a broad range of frequencies as shown by the blue green shading.
The SETI@Home Screen Saver performs an averaging procedure called "Baseline Smoothing" that eliminates Broadband Noise and brings all the other narrow bandwidth events down (or up, depending on the size of bandwidth) to a common "baseline" level. Also, sometimes the data from Arecibo as a whole gets slowly louder and/or softer over time. Baseline Smoothing evens out this effect as well. In the graph to the right you can see that the range of frequencies that has been captured is fairly small. Especially when it is compared to the other graph. Again, the blue green shading is showing where we are getting a signal.
If this is still hard, um, lets see … How about this, if you tap one key on a piano you will get one frequency. That is a Narrowband Signal. Just one tone (well, lets not get into the harmonics or I will never get done here). Now, how about when we slam down on all of he keys? Besides being noisy, annoying, and horrible; it is also a Broadband Signal.
