grokking mid-side
Today I really grokked the mid-side miking technique for the first time.
OK. You have 2 ears. Stereo has 2 speakers. If you're recording a piano, you might put up 2 microphones, whose 2 lines feed into 2 channels that go to your 2 ears. Then you hear the piano in stereo, which is something like what you might hear in real life.
But there are problems. Since each mic is picking up a slightly different signal, but includes some of the same, the math gets thorny about phasing. Usually no problem, but sometimes, even in today's world, you might wind up with a one-speaker situation, in which case you're summing that stereo to a single mono line. In the summation, some notes or frequencies may get weirdly emphasized or may disappear.
Think of it this way: two identical waves with a volume of 3 in the left and right channel may coexist when going into different ears. But once you put it in mono, they get way louder because they sum. But if the mics are placed just so, they might be out of phase, so the left channel's 'up' hits right at the right channel's 'down.' Then it gets softer, or disappears.
Most of the time, of course, it's not that pure, so you get comb-filtering. That's the sound equivalent of when you put two screens on top of each other and odd patterns emerge. Same thing with sound waves. It can get ugly.
So. How to solve it? You want big rich stereo on headphones or earbuds or speakers, but you want it to sum well to mono.
Aha. Enter the mid-side technique. Fiendishly clever. Instead of arraying 2 mics more or less like a pair of ears, do this: Put one mic front and center. Then put the other mic facing side-to-side.
The top mic picks up only from the front. The other picks up from both sides, even though it's only one mic.
Then you create 3 tracks in your app: one for the center mic, and two twin versions for the side mic. The center mic you pan center (which, of course, means that it's sending identical signals to both your speakers). The side — ahhhhhh the side!!! Here's what you do. Pan one of the twin tracks left, and the other right (which, again, means it's sending identical signals to both speakers). Then, crucially, reverse the polarity of one of them.
So now, right when one sound wave is going up, the other one is going down. You know what happens then, right? Well if they're on the same channel . . . silence. They cancel each other out completely. But if they're on different channels, they just create a nice tickly mono sound. Not stereo, because obviously it's all coming from one mic. But, since they're reversed, they enter the ear weirdly and it has an odd effect.
Then, you combine it all together. The two reverse-polarity tracks (recording all the sounds that came in from the sides of the room) and the center track (recording the piano that's right in front).
Think about it: remember how identical things cancel each other out and create silence. OK. Everything in the center channel that's matched on the left side gets cancelled out, and everything on the center channel that's matched on the right side gets cancelled out.
This gives you a "stereo-ish" feeling. But, since your fig-8 mic is really a mono line, it's not gonna give you a true stereo image. . . . Right?
Wrong. Remember polarity. Some of those sounds coming in from the left side aren't just the reverse of the sounds coming in from the right side. They're different sounds, different reflections from the room. That's what gives you the feeling of being *in* the room. But of course it's all coming from one mic, so it's not two completely different images, the way it would be if you had two mics facing in those opposite directions.
So it's not the truest stereo, but it's not not stereo either. And — here's the amazing part — when you do put it on one speaker, poof. all the conflicting noises that would phase in the usual 2-mic pattern don't phase because . . . they cancel each other out perfectly. You wind up with a beautiful perfect mono image. No weird effects or losses.
It feels great, because you're getting all the ambience that's bouncing off the walls, and a strong image — but since it's all coming down one line [albeit polarity-shifted] it reads as very centered.
I've never done mid-side. I've always been happy with the usual way. But I started wondering: what if you strolled back and forth right in front of the thing? Would it read as stereo back-and-forth strolling, the way it would with a stereo pair? Or would it just tickle?
Today I tried it.
Hey. It DOES give a moderate stereo image, just with a little bit of left presence on the right side and vice versa. Mann!! I tested it myself, walking back and forth and back pretty close to the mics, then again a few feet away.
It's true stereo!! All because of math. It's a little less 'natural' at this distance than a stereo pair would be, but there are distinct advantages. Crazy!!! The polarity of the diaphragm creates a subtle directionality. You can hear it.
Check it out:
Three passes
1. just the center mic
2. just the side mic, polarity-rev'd and panned
3. both: the full mid-side
There it is! True stereo. I compare it to the color photos you see that were done in the 1870s or something: it's really a response to the stereo image the way the color photos are real color. But it's not like the 'true' color you'd see in a standard photo today.
Wow. I'm just glad I finally understood it. As with many things, you have to do it to really get it.
And here is how the piano sounds. First mono, then the stereo fades in in around 5 seconds: Piano
OK. You have 2 ears. Stereo has 2 speakers. If you're recording a piano, you might put up 2 microphones, whose 2 lines feed into 2 channels that go to your 2 ears. Then you hear the piano in stereo, which is something like what you might hear in real life.
But there are problems. Since each mic is picking up a slightly different signal, but includes some of the same, the math gets thorny about phasing. Usually no problem, but sometimes, even in today's world, you might wind up with a one-speaker situation, in which case you're summing that stereo to a single mono line. In the summation, some notes or frequencies may get weirdly emphasized or may disappear.
Think of it this way: two identical waves with a volume of 3 in the left and right channel may coexist when going into different ears. But once you put it in mono, they get way louder because they sum. But if the mics are placed just so, they might be out of phase, so the left channel's 'up' hits right at the right channel's 'down.' Then it gets softer, or disappears.
Most of the time, of course, it's not that pure, so you get comb-filtering. That's the sound equivalent of when you put two screens on top of each other and odd patterns emerge. Same thing with sound waves. It can get ugly.
So. How to solve it? You want big rich stereo on headphones or earbuds or speakers, but you want it to sum well to mono.
Aha. Enter the mid-side technique. Fiendishly clever. Instead of arraying 2 mics more or less like a pair of ears, do this: Put one mic front and center. Then put the other mic facing side-to-side.
The top mic picks up only from the front. The other picks up from both sides, even though it's only one mic.
Then you create 3 tracks in your app: one for the center mic, and two twin versions for the side mic. The center mic you pan center (which, of course, means that it's sending identical signals to both your speakers). The side — ahhhhhh the side!!! Here's what you do. Pan one of the twin tracks left, and the other right (which, again, means it's sending identical signals to both speakers). Then, crucially, reverse the polarity of one of them.
So now, right when one sound wave is going up, the other one is going down. You know what happens then, right? Well if they're on the same channel . . . silence. They cancel each other out completely. But if they're on different channels, they just create a nice tickly mono sound. Not stereo, because obviously it's all coming from one mic. But, since they're reversed, they enter the ear weirdly and it has an odd effect.
Then, you combine it all together. The two reverse-polarity tracks (recording all the sounds that came in from the sides of the room) and the center track (recording the piano that's right in front).
Think about it: remember how identical things cancel each other out and create silence. OK. Everything in the center channel that's matched on the left side gets cancelled out, and everything on the center channel that's matched on the right side gets cancelled out.
This gives you a "stereo-ish" feeling. But, since your fig-8 mic is really a mono line, it's not gonna give you a true stereo image. . . . Right?
Wrong. Remember polarity. Some of those sounds coming in from the left side aren't just the reverse of the sounds coming in from the right side. They're different sounds, different reflections from the room. That's what gives you the feeling of being *in* the room. But of course it's all coming from one mic, so it's not two completely different images, the way it would be if you had two mics facing in those opposite directions.
So it's not the truest stereo, but it's not not stereo either. And — here's the amazing part — when you do put it on one speaker, poof. all the conflicting noises that would phase in the usual 2-mic pattern don't phase because . . . they cancel each other out perfectly. You wind up with a beautiful perfect mono image. No weird effects or losses.
It feels great, because you're getting all the ambience that's bouncing off the walls, and a strong image — but since it's all coming down one line [albeit polarity-shifted] it reads as very centered.
I've never done mid-side. I've always been happy with the usual way. But I started wondering: what if you strolled back and forth right in front of the thing? Would it read as stereo back-and-forth strolling, the way it would with a stereo pair? Or would it just tickle?
Today I tried it.
Hey. It DOES give a moderate stereo image, just with a little bit of left presence on the right side and vice versa. Mann!! I tested it myself, walking back and forth and back pretty close to the mics, then again a few feet away.
It's true stereo!! All because of math. It's a little less 'natural' at this distance than a stereo pair would be, but there are distinct advantages. Crazy!!! The polarity of the diaphragm creates a subtle directionality. You can hear it.
Check it out:
Three passes
1. just the center mic
2. just the side mic, polarity-rev'd and panned
3. both: the full mid-side
There it is! True stereo. I compare it to the color photos you see that were done in the 1870s or something: it's really a response to the stereo image the way the color photos are real color. But it's not like the 'true' color you'd see in a standard photo today.
Wow. I'm just glad I finally understood it. As with many things, you have to do it to really get it.
And here is how the piano sounds. First mono, then the stereo fades in in around 5 seconds: Piano
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