I recorded this sound using a Neumann U87 microphone through an Avalon M5 preamp to my Mac. Believe it or not, it's actually just my voice - recorded many times. I did my best to change the pitch and sound of each voice. I think I did over 50 tracks to make the sound. After I recorded several tracks of voice, I would pan each track to a different spot in the stereo spectrum, then mix down to a single stereo track. Then I imported the track in and started all over again until I had the right amount of layering. The trick was to yell words that were unintelligible. If you heard a single track of this you would probably laugh! Lots of mumbo jumbo! Perfect for an angry crowd background ambience!
Here's the recording: Angry Crowd