Conversation Music Theory How does the man help the woman understand the meaning of"antinoise"?

W: Welt, I don’t know about you, but I’m totally confused about today’s lecture, especially the part about music and noise.
M: It’s not so bad, really. I think I got most everything in my notes.
W: So then ... what is the difference between music and noise? Professor King said noise is a random sound, but then he said the sounds of a cymbal and a drumbeat were examples of noise. I’d say they’re examples of music—since they’re sounds made by musical instruments! What do you think he meant?
M: OK. Do you remember how he said that noise is a random sound?
W: Uh-huh.
M: Well, it’s a random sound that has irregular sound waves.
W: But how’s a sound that’s noise different from a sound that’s music?
M: Well, if you could take a picture of a musical note, you’d see that it has regular waves that repeat themselves. That’s because music is a sound that’s in a pattern we can hear or discern. Noise is different from music because it doesn’t have a pattern.
W: But why is the sound of a drumbeat noise instead of music? Isn’t a drumbeat a note? And then ... so ... doesn’t it have a regular pattern of waves?
M: Maybe you’re taking what he said too literally. Maybe he meant a drumbeat is as close as a musical instrument can get to making just noise.
W: Maybe a single drumbeat is like a word spoken out of context. A single word with no context is just noise!
M: Now there’s a thought!
W: The other thing I didn’t get was what he said about antinoise. First noise, then antinoise? What do you think he meant?
M: Think of it as the opposite of noise. It’s like—wait, let me back up. Sound has waves, right?
W: Right.
M: Well, we can describe these waves as "in phase" or "out of phase" with each other. "Out of phase" means reversed.
W: Uh-huh.
M: If you add two out-of phase waves together at the same frequency, the result is antinoise—silence.
W: Antinoise is silence?
M: Right! And there’s a computer program that proves this. A microphone picks up the sound and sends it back to the computer, and then the computer reads the waves and makes sort of a mirror image, or a reverse copy of the wave. Then you can play it back against the original sound, and when the two waves meet, they sort of overlap each other ... exactly at the high and low peaks. This eliminates the sound, creating zero sound—antinoise.
W: How do you know all this? Professor King didn’t talk about this.
M: It’s all in our book. Didn’t you do the reading?
W: No, I didn’t have time. I guess I’d better do that now.
M: Yeah, you should. But it’s better to do the reading before the lectures ’cause then you’ll have a better idea of what he’s talking about.
W: Yeah, you’re right. I guess I have some catching up to do.