This. It helps to think of the crowd as a team, and the noise is a product of the team's constant participation. We all work together to create that oppressive blanket of noise, and the volume in a particular moment is less important than the constant production of sound that disrupts the opposing team's communication. Different octaves, different notes, different tones - it's all good, the crowd's got that covered - the goal is simply to fill in that wall of noise with every kind of sound we've got.