The QC's don't completely wash out background noise. If you listen to your music loud enough (which is probably too loud), you literally won't hear anything around you. But normal use, I find that it muffles outside voices enough not to get distracted, but not so much to the point where if someone says my name I can respond. An added plus, is people will bother you less if you're wearing them. Sometimes I like wearing them without listening to any music, just to create a quieter environment.