I’m taking a class called “Fundamentals of Audio Engineering” this quarter with a guy named Rick Wyffels. He’s a nice guy, and really flexible when necessary. (He also makes interesting sound effects to demonstrate things, and gets off track to tell stories.) On Monday he gave back our second quiz. I got 9.75 out of 10, with half credit for one out of 20 questions. I couldn’t see what I did wrong with that question, so I talked to him afterward to find out. The question was about how balanced audio signals reduce noise using three wires. Apparently the problem stemmed from the fact that I know something more about electronics and how this actually works than he does. I wrote an answer that, to my mind, said the same thing as what the book said, just a little more specific about how it actually works. He didn’t quite agree, and said I should memorize the book’s definition for the midterm. He turned over the quiz to see my score, and said, “Ohhh, I see what you’re doing. You want a perfect score…” It’s not that I care that much about having a perfect score; anything above 90 is enough to assure an A. I just want the truth to be known. I still thought I was right, and he gave me the half-point back. Then when he went into his spreadsheet to update my score, he saw that I had also gotten a perfect score on the first quiz, and groaned, “Oh, boy…” He said he’d ask someone he knows to explain to him how the concept actually works.
Wednesday we had another quiz. I checked over it before handing it in to make sure I hadn’t said anything he could mark me off for. He accepted my quiz with what I can only (inaccurately) describe as a posture saying “what are you up to this time, you troublemaker?” and proceeded to flip through it, which he didn’t do with anyone else’s quiz. He was obviously checking it over to see if I had made any errors by which he could declare triumph. Above one question I had written a note of clarification: “One assumes we’re talking about compressors here, though it doesn’t say…” When he read this, he laughed out loud, and then announced this fact to the rest of the class (for those who hadn’t finished yet). “One every quarter…” he muttered, which I could hear from my place in the second row. When he was done looking through my quiz, apparently without finding any errors, he gave me a grin and a thumbs-up. “Gotta watch you every minute…”
It’s fun being smart.
So your response was something to the effect of 1 wire to shield from noise, the other 2 to carry the signal (+ and -). *shakes head*
Congrats on being thmart!
That’s the basic idea, but there’s more than that . The shield is also the ground, against which the two opposite copies of the signal are referenced. At the receiving end, the + and – signals are subtracted, which has the effect of canceling out any noise that occurred equally on both wires, since the two wires always have the opposite signal from each other. He took issue with the fact that I conveyed it as being an act of subtraction that kills the noise that’s shared between the wires, whereas the book’s definition simply said the difference of the two signals was used, and the noise was blocked, which he thought meant noise only occurred on one wire.
pwn ‘im in the face Tim!
flippn’ genius, whoever figured that one out btw.
Simple, but elegant, and quite thorough! (Provided your twisted pair picks up identical noise)