[maikaru]

When we hear the Audience in the Live DVDs, the Audience is being fed through special microphones placed throughout the venue to capture the sound of the audience, usually dubbed "Audience Mics". Normally, the microphones given to the singers and to the drums are specially designed to only pick up the singers voice or the sound of the drums. Anything outside of the range of pick-up for these microphones cannot be heard. The guitar, bass, and keyboards are almost always plugged in directly through the sound board, so no outside noise - audience, vocals, or otherwise - will be captured. It looks like they chose either not to use them, or not to mix in the audience noise from the microphones in the stadium.

We are hearing exactly what Ayu hears on stage - no audience at all. The only time a singer is able to hear the audience is when they take out their ear monitors.