[00:00.00]W: Well, I don’t know about you, but I’m totally confused about today’s lecture, especially the part about music and noise.
[00:08.00]M: It’s not so bad, really. I think I got ‘most everything in my notes.
[00:12.20]W: So then ... what is the difference between music and noise? [00:15.80]Professor King said noise is a random sound, but then he said the sounds of a cymbal and a drumbeat were examples of noise.[00:22.22] I’d say they’re examples of music—since they’re sounds made by musical instruments![00:26.54]What do you think he meant?
[00:28.10]M: OK. Do you remember how he said that noise is a random sound?
[00:32.28]W: Uh-huh.
[00:33.27]M: Well, it’s a random sound that has irregular sound waves.
[00:36.95]W: But how’s a sound that’s noise different from a sound that’s music?
[00:40.89]M: Well, if you could take a picture of a musical note, you’d see that it has regular waves that repeat themselves. [00:47.60]That’s because music is a sound that’s in a pattern we can hear or discern.[00:52.00]Noise is different from music because it doesn’t have a pattern.[00:55.57]W: But why is the sound of a drumbeat noise instead of music?[00:59.60]Isn’t a drumbeat a note? [01:01.12]And then...so...doesn’t it have a regular pattern of waves?
[01:05.29]M: Maybe you’re taking what he said too literally.[01:08.34]Maybe he meant a drumbeat is as close as a musical instrument can get to making just noise.
[01:13.82]W: Maybe a single drumbeat is like a word spoken out of context. [01:18.12]A single word with no context is just noise!
[01:21.12] M: Now there’s a thought!
[01:22.52]W: The other thing I didn’t get was what he said about antinoise. [01:25.72]First noise, then antinoise? [01:27.92]What do you think he meant?
[01:29.12]M: Think of it as the opposite of noise.[01:31.52] It’s like—wait, let me back up. Sound has waves, right?
[01:37.72]W: Right.[01:38.42]M: Well, we can describe these waves as “in phase” or “out of phase” with each other.[01:43.12]“Out of phase” means reversed.
[01:45.52]W: Uh-huh.
[01:46.32]M: If you add two out-of-phase waves together at the same frequency, the result is antinoise—silence.
[01:52.12]W: Antinoise is silence?
[01:55.00]M: Right! And there’s a computer program that proves this. [01:58.12]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. [02:08.92]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.[02:18.52]This eliminates the sound, creating zero sound—antinoise.
[02:23.32]W: How do you know all this?[02:24.82] Professor King didn’t talk about this.
[02:26.82]M: It’s all in our book. Didn’t you do the reading?
[02:29.82]W: No, I didn’t have time. [02:31.62]I guess I’d better do that now.
[02:33.42]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.
[02:40.42]W: Yeah, you’re right. I guess I have some catching up to do.
托福14天冲刺微信战团