Number crunching with Pixel Bender

Does anyone have experience using PixelBender to crunch numbers in AS3? I’ve built a simple synth, and when I added in a 4-pole lowpass filter function, calculation times for writing 2048 samples to the audio buffer increased from 5-6ms all the way to 24-29ms. Unacceptable!! I’m wondering if anyone has done anything similar?

I asked adobe on the PixelBender forum, but they are very slow to respond.

Here is my response post, including the source code, so you can see how it works, along with a link to the synth.

http://www.adobe.com/cfusion/webforums/forum/messageview.cfm?forumid=72&catid=661&threadid=1414451&enterthread=y#5173854