Lelouch never spoke the way he does now in front of Nunnally, and has the helmet distortion.
Even if you bring the 'I'm blind, so I listen better', this is aboiut a very different sound, not picking up small ones.
So many people failed to make the comparison.
When he screamed in the end though, she seems to have been surprised.
By the way, best scream of Despair by Lulu ever.