What's the difference between diffusion and absorption?

1:16 talk to you about acoustic treatment, the differences between absorption and diffusion. What are thosethings on the walls of recording studios? That's basically what I want to talk about a little bit today.So I've covered this in some other episodes because I've built my own home studio and I'vebuilt other studios in the past.

1:35 And I got a little technical and I kind of want to zoom out and just say like, OK, what are these things? What are they trying to do? So you've probably seen examplesof musicians with a bunch of like egg cartons on their wall.

1:52 And that is their most basicversion of trying to accomplish this, of trying to instead of having audio slap from one wall onto the next instead of having that sound wave just like slam into it and reflect right back like picturelike a mirror.

2:07 You know that weird feeling you can't when you look into a mirror that's pointed at another mirror and it just goes on and on and on for infinity. Same thing happens with sound whenyou have two just parallel walls. The sound just reflects back and it creates this thing called aflutter echo and it is incredibly harsh and very, very difficult to get out of an audio signal.

2:30 So when we're recording stuff, you want to avoid that most of all because that is just kind of death.It doesn't sound good, doesn't have vibe and it's very difficult to manipulate.

2:42 On the other end, if it is a completely dry signal, you can always add more stuff back.And the beauty of modern recording is say that you get something as perfectly dry as in there'sno room sound whatsoever. The space that I'm in does not have that because I don't have enoughmoney.

2:58 But if I were to be kind of cool, it's like almost like a padded room like you're recording into a giant pillow. That sound allows you the ability to drop in a virtual

3:11 soundscape. So you can say, I want this to sound like I'm in the Taj Mahal and boom,sounds like the Taj Mahal or I want to be in Notre Dame, the church. It's like boom, there you go.It is the most flexible because it is a pure quote unquote audio signal.

3:28 So those are kind of the two extremes. You have the harsh flutter echo and the pure

3:35 dead room. The pure dead room though has its drawbacks because it sounds unnatural. That is avery strange space to be in. So most recording studios try to find somewhere in between. It's a littlebit live as in it sounds like you're in a live real world space, but it's a little bit dead as init sounds, it's like easy to manipulate. It doesn't have so much character.

4:00 And so a lot of the home recording studios are trying to split that gap because you don't want your room to have toomuch character to sound like it's a church or something like that because then you're onlygoing to be able to make a certain type of music or everything that you produce has to come outthat way. It is also a very bad environment to mix.

4:17 So mixing as I've covered in other episodes is kind of the process of pulling together music and all the different track by tracks so that itbecomes a cohesive record, a cohesive song.

4:31 It adds that element of I can play this on any speaker,any setup and it's going to sound cool, it's going to speak and recording and mixing in the same space usually leads you to having more of a dead room, more of a neutral room. Because whenyou're mixing, you want to really hear the stuff. You don't want to just hear your room.

4:53 And so for those two kind of like reasons, that's why most recording studios, especially the onesthat are combo studios, recordings like live room slash mixing room, those are going to be more onthe dead side. So how do we get things more dead? So back to the egg shell example that is like thecheapest possible and it kind of works.

5:15 What those kind of things do is they send the sound waves in a bunch of different directions, but they're only sending the weakest of the sound waves away.

5:25 So to the naked ear, it might sound better but when you put a microphone in a room like that,it's going to sound bad because the microphone is going to reveal a bunch of other things,these bigger, more powerful low frequencies. Low frequencies oscillate at a slower rate versushigh frequencies would oscillate in a higher rate.

5:44 The higher rate frequencies are easier to absorb, easier to diffuse, easier to push around the room, easier to fix the problems. The big stuff,

5:54 that's the reason why if you, you know, live next to a train station, you can have as doublepain windows, you can do all the things, but the big booming low frequencies that train is going tocut through, pretty much no matter what you do. To combat that, that's where studios get really,really expensive because it's not really just about putting stuff on the walls.

6:16 It's about building a room inside of another room. It's about creating the space that those big, all low frequenciescan't reach through. So that's the difference between soundproofing and what we're talking abouttoday. What we're talking about today is the stuff that's on the walls. Why do you have the stuffon the walls? It is not to keep every sound in the world out. That is impossible.

6:42 It is instead to make the best of what you got. Most people are recording the bedroom. That's what I'm doing. I'vegot a bedroom that I've converted into a recording studio. I'm very, very glad that it is no longerthe room in which I also sleep, but that was how I was for a long time. But now, because it isn't,I am able to hang all these things on the walls.

7:01 The key for what I'm trying to do is a little bit of diffusion, a little bit of absorption, but mostly absorption. So what is absorption? Absorptionis soaking up the sound. Absorption is deadening the room. Diffusion is sending the sound wavesin a bunch of different directions.

7:18 So I want a little bit of the diffusion to keep the room feeling live, give a little bit of character, get rid of that flutter echo, that awful, awful sound.But I mostly want the absorption so that my room doesn't end up being this big boomy boxy mess.

7:36 And the perfect example are those H shell cartons. Those have almost zero absorption because they'reso tiny, even low mid frequencies, those frequencies require a pretty dense amount of materialto absorb, to deaden, to stop. And that's why most of my panels around my room are betweensix to ten inches because it takes away square footage from your space.

8:12 So that's part of the reason why recording studios are expensive. You have to have a pretty bigspace. You're going to give up a bunch of square footage just on stuff that you're hanging on thewalls and those are thick. They're not picture frames. And you might see this out, just acousticpanels of a restaurant or something like that. They're usually too small, especially for music.

8:33 They are just dimming a little bit of the high frequencies, a little bit of that flutter echo.They're making it a slightly nicer space. But what I'm trying to do, like recording an acousticguitar or the human voice, there's a bunch of stuff that gets picked up by that microphone,and you need to get rid of it. You need to absorb it. And so that's why we hang this stuff up.

8:53 But one of the cool things that you can do in these spaces is to think about the principleof parallel walls. So instead of covering every square inch with absorption materials, you caninstead stagger the panels. So you have one panel and then a blank wall directly opposite of it,and then a panel and then a blank wall on the opposite side of that.

9:15 So it's kind of like a zigzag between the two walls talking to each other. So you never have one mirror facing another mirror,so to speak. You never have one blank wall facing another blank wall. You instead have a oscillating

9:29 of panels that basically eliminate the need to maybe you can buy half as much. And these panelsare not cheap because the materials that are inside of them are just any old thing. They're patentedacoustic materials. They're dense materials. One of the names is Rockwool or Roxul.

9:50 And this stuff is like think heavy insulation kind of junk that you put inside of these boxes of plywood.And then you cover it with a fabric. But if you just put boxes and you put feathers or somethingon it, it's not going to do the job. It'll do something, but it's not going to do enough.

10:14 And you need some powerful stuff in order to do anything. It's kind of amazing just stepping into this bedroomthat I'm in versus the one right next to me. It's like a totally different vibe. You can hear yourheart beat differently just by having, you know, how many panels do I have? 13, 14 panels.

10:33 And thenI also have this crazy looking column thing that nobody's ever going to see unless I guess I'd do like a 360 video in here. But I stuck it into the worst corner. So one of the other principlesof sound is that corners are the enemy. So in a really pro recording studio, you'll notice thecorners are not sharp.

10:53 They design it on purpose because think about it in terms of like that mirror effect. The corners are the ultimate worst possible case because it's boom, boom, boom, boom,things get stuck in that corner. And to combat that, we use things called bass traps. And thisand this sucker is like two feet by two feet.

11:16 It's like this huge column that fix the worst problem area of my room and then allowed me to start recording drums in here because drums,

11:25 you know, everybody's heard drums, live drums, they're loud, they're bold. They have every frequencyand they are the hardest thing to record probably out of everything. And part of that is becausethe rooms can be very unforgiving with that much volume and with that much frequency spectrumall going on at the same time.

11:47 So by putting my big old bass trap column, it's absorbing so much of what's going on in this studio. It is giving me the effect of, you know, probably four of thesepanels, but in my most problem area. And it's a really funny thing too when you are putting up thesepanels is that every time you put one up, you find a new problem area.

12:07 It's so frustrating where you're like, oh, it's these parallel walls. I'll fix those parallel walls. I'm like, okay, that's fixed.

12:13 But now I hear weird things over in that corner to my right. So let's put something in the corner.It's like, oh, wait, now the ceiling, I'm hearing something weird. Let's put down some carpet.And it's like, oh, it's not enough. All that corner over in the top left hand. I got to put somethingup there.

12:28 It is this game of whack-a-mole that each problem is revealed by fixing the problem previous, which maybe isn't metaphor for life. But that continuous improvement, it adds up and itisn't like linear. It is quite a progression in terms of just every panel that you put up in.The space becomes exponentially more recordable.

12:51 I'm sure that there is a point of diminishing returns like a point at which you put up too many panels and like I was saying it becomes toodead or it becomes almost hostile or sterile like a place that you don't want to be in all the time.But again, these panels are expensive.

13:07 I had to do my PayPal credit card in order to afford these things. And so that problem doesn't exist for me. But I'm sure that other people have that.And it's a blessing of course, because yeah, it's more flexible. But by having a more

13:24 live space, you impart at least a little bit of the character of the room in the recording.And I think that that's actually really cool. Maybe there's certainly too muchwhere then it becomes inflexible. But having something sound like the place that you're recording inis just something that attaches you to music history.

13:47 It's like people will want to record there or people want to visit there. It'll become like a museum or it'll be even just in your ownpersonal life. That's like part of your diary. It's like I remember what that room sounded like.

14:01 Even if that building gets torn down, it's like that is impressed upon the record. It's part ofthe sonic fingerprint. And so to do that, we turn from absorption to diffusion.

14:13 So diffusion is the process of scattering the sound reflections versus absorption of convertingthat sound energy into like heat. Basically taking the sound and making go away.

14:26 And so by doing both, you're able to maintain that sense of space. You're able to keep thatairiness in the sound and you are able to avoid the harsh reflections. And diffusion happensin a bunch of different ways. Like literally just have you noticed when you move into a newapartment or whatever, and it's unfurnished, and then you put your furniture in there.

14:47 And it's wow, that's super different. There's absorption going on. Like you put in a big couch in a room.

14:53 That's a whole bunch of fabric and stuff inside those cushions and whatever. That is soaking up sound.That is converting sound. But then you also maybe put up a bookshelf.

15:05 Hey, and that bookshelf, all of those books are slightly different. And now the sound hitsthose books, all the different spines of the books. And it goes off and scatters in a milliondifferent directions because it's not all encyclopedia said. It's a bunch of differentrandom books that you've collected.

15:20 Or like in my example, I've got a bunch of records behind me, that's kind of like it's own little mini-viewed version of diffusion, where it's sending the soundsoff into different areas. Diffusers also can be purpose-built. And these are the coolest ones.I don't actually really have something that is too much like this.

15:40 They're usually used for bigger, more live spaces. But they have these quadratic diffusers that are basicallythey use math to be able to laser etch. Like it's basically either wood or plastic to createthese irregular surfaces.

15:59 And then the sound hits that and it is mathematically proven to scatter the most. And so you put a few of those around the room and you're able to maintain that sense ofspace, but it's smoother. It also makes it a room sound a little bit bigger.

16:20 It's like kind of like picture disco ball, right? Like the light is hitting the disco ball. It'sgoing in a million different directions versus the light pointing light into something superdense. And the light just kind of goes off for pointing the light into a cloud and it just kind ofdiffuses in.

16:42 So it's the difference between redistributing energy as in diffusion and removing energy as an absorption. And I really feel like they're both kind oflevers. You need to pull and keep aligned with your goals. You don't want things to be too dead.

17:03 And also maybe you don't want things to be too reflective. So I think understanding thedifference, understanding which tool to bring. And then also understanding that actually soundproofing as in removing your all of the external sounds from getting in and all of your soundsfrom getting out, that is so cost prohibitive.

17:26 It is you essentially have to build a room inside of a room. You have to decouple things. You have to take away resonances. Because like pictureI don't know, like my place, there are a bunch of beams that go across the second story.

17:42 And sowhenever I do something in this room, it's going to hit some of those beams and that sound wave is going to connect. It's like a support beam. In order to not have that happen, I literally haveto somehow decouple these vibrations from that beam because crazy amounts of money. That's whatthe really really big studios are all about. And I mean there are things that you can do, right?

18:08 Like you can put on heavier curtains around your window. You can do double-paint windows. I havea little insert that I put below my door that cuts off the airflow underneath the door. Andthat was a big deal because now my wife can like watch Netflix downstairs and I can keep working

18:28 before there was just so much spill. So it's like a problem that you manage but you also recognizesoundproofing. It's just like waterproofing. It's like good luck. But sound sweetening with absorptionand diffusion. That's the move. So hopefully this helps a little bit. In terms of you know,cheap ways to do that, the bookshelf thing is a tried and true method of diffusion.

18:54 It's not perfect but it helps. And the absorption thing like shag carpet, big couch, you know, those thingshelp too. But the thing that really helps with the absorption because you're trying to target thosebig frequencies, big old sound panels professionally made sound panels or at least professionally sourced.

19:15 You can make them yourself. I've made them. It takes a while but you can do it. And it's cheaper butnot that much cheaper. There's a reason. There's a reason why studios look the way they do.Ideally, you have a space that doesn't have too many parallel walls or any.And daily, you have a space that has rounded corners instead of sharp corners.

19:39 And the space that is completely decoupled from the outside. But what's one of us is actually living in an ideal setup.And you don't really need it, you know, like the stuff that I'm making, I'm making in this room andI think it sounds good. Does it sound perfect? No. But that's kind of cool too. Because it sounds likehere. Hope you enjoyed the podcast.

20:00 Definitely want to invite you to subscribe to it and tell your friends. This is Love Music More. We're here every Tuesday.

20:23 If you're interested in pursuing, pursuing music or even just putting a cover song out there ora karaoke track or whatever, it's fun times. It's like a really cool thing to be able to putyourself up on Apple Music or Spotify or whatever. So anyway, thanks for listening and I'll see younext week.