Here's an intersting article (although a few years old) which was written by Rick Turner, who visits this forum occasionally. at least, I think it's the same Rick Turner, but I'm not 100% sure.
Anyway, the article mentions the FRAP system about half-way in.
http://www.acousticguitar.com/issues...fication.shtml
Here's a link to the Trance Audio website, which was mentioned as the modern successor to the FRAP. I've never seen one of these in the flesh, so all I can do is point you toward the website.
http://www.tranceaudio.com/