The 'uncompressed' stream has already been winnowed down substantially: there's a lot of processing that happens on the detectors themselves to decide what data is worth even sending off the board. The math for the raw detectors is 100 million channels of data (not sure how many per detector, but there's a lot of them stacked around the collision) sampling at 40Mhz (which is how often the bunches of accelerater particles cross). Even with just 2 bits per sample, that's 1PB/sec. But most of that is obviously uninteresting and so doesn't even get transmitted.