Sound Occlusion Analysed
Sound Occlusion Analysed

It’s no secret that a few years ago, Counter Strike’s audio was terrible. The HRTF update
last year improved things massively by helping you to pinpoint which direction sounds were
coming from. This occlusion update further builds upon the sound model by muffling and
quietening sounds that come from behind walls. Firstly I’d like to talk about a bug that
was discovered last month, which I believe could have been responsible for this update.
In a popular reddit post, Jambo revealed that footsteps from behind walls wouldn’t be
heard if the player model wasn’t being rendered. I wonder if this was a trade-off that Valve
were aware of. You see, there was an EVEN OLDER update that
was introduced to stop cheaters. Wallhacks can be used to see people through walls. The
update made it so that information about other players would only be sent to a player’s
PC if they had a direct line of sight to them. These visibility calculations are all done
server-side, meaning that the cheater’s computer would be getting literally no information
about players behind walls, rendering the cheats ineffective.
You may have encountered this anti-cheat method if you’ve ever played a match with a high
ping. Sometimes you’ll run around a corner and enemies take a while to ‘pop’ into
view because it takes a while for the server to realise you need the other players’ information.
It doesn’t seem fair, but in a way it’s more so. And it shows that the anti-cheat
is doing its job. However, with this information block in place, it does mean that footstep
sounds are also out of the question, unless the server decides to send you them separately.
This link between this anti-cheat and the footstep bugs is just speculation on my part.
But what I do know is that footsteps can now be heard even when a player’s model isn’t
being drawn. This fix was rolled out just days after the bug was discovered and is separate
from the occlusion update. This isn’t necessarily the case, but I wonder if the footstep fix
was just a temporary solution and if the new occlusion method is a more robust, cheat-resistant
method of tackling the problem. But I’d like to make it super clear, this is all just
speculation. It could just be that Valve are nice and want to treat us to better audio
and that its timing with the other bug is just a coincidence.
Any way. Even without enabling occlusion I can show that this bug has been fixed and
that the footsteps play regardless of whether the character model is being drawn or not.
Just to make sure, I made my own worst-case-scenario level comprising of 2 separate rooms. When
I say these are separate, I mean it! There’s empty space between them. Pure NOTHINGNESS-
a complete vacuum! Technically, sound shouldn’t be able to pass through this in the first
place but, for the sake of maps, it should be able to since there is often an empty space
like this between areas on a map. And indeed, it does. Even without occlusion,
so it shows that the footstep update is doing its job. I also noticed an awful lot of headshot
sounds that shouldn’t have been there- turns out that if you fire a gun in a vacuum on
CS:GO then not only does it violate the laws of thermodynamics but you also get quantum
bullets that are seemingly in 2 positions at once or something. Either that or 2kliksphilip
is cheating. It’s been 3 minutes 24 seconds and I haven’t
even started with the occlusion yet. But I will now. If this same sequence I just showed
is played again but with occlusion enabled, you can hear the difference that it makes.
The sounds are muffled and bassier. According to Valve’s blog, this isn’t
just a cheap trick- it distorts the sounds based on the materials it’s travelling through!
And it’s impressive stuff- the material type does make a difference, as does its thickness.
Strangely, wood doesn’t muffle as much as stone when both are 16 units thick, yet does
a much better job when they’re both 128! The sound even takes into account indirect
paths, it seems. I’ve kept the closest wall transparent just so you know what’s going
on behind. Adding a roof didn’t make much difference in this case, though if he were
higher up towards the top of them then it would have.
All in all from the testing I did I was impressed with the system. It’s just that everything
I tested raised more questions and I didn’t have time to delve too deeply into everything.
Just know that what Valve have done is pretty cool.
Next up I made ANOTHER map to test the direction the sound comes from. Will it come directly
from the shooter, or can we hear echoes in this game? Because in reality, if you’re
stood here, looking directly through the wall towards the shooter, then the sound should
appear to come from the left as it’s bouncing off the walls to reach you. The ingame sound
debugger shows this isn’t the case, and here’s a clip for you to hear it yourself.
In other words, this is a limitation with the occlusion model. It always comes from
the direction of the shooter, when in reality the sound would appear to come from somewhere
else. I’m not complaining though- do we really want it to be harder to tell where
sounds are coming from?! We’ve spent years moaning about that very issue!
Honestly I’m very impressed with this new sound system. It nicely calculates the distance
and type of sound it is, and muffles it according to the number, thickness, material type and
position of the walls around it. It’s not quite as flashy as the Aureal A3D demo but
it suits CS:GO’s sound requirements nicely. It’s better than I first gave it credit
for, too: I repeatedly think that I’ve tricked it, only to find with further testing that
I haven’t and it’s more advanced than I expected. It doesn’t just take into account
the direct line between you and the sound-source, but also the surroundings and it muffles and
distorts the said sounds accordingly. I don’t know how else to put it, it sounds RIGHT.
Though I suspect that at first, some people may not like it. Just like with HRTF. You’ll
just have to get used to the new sound system and to master the maps you wish to play on.
Do this and I believe this new occlusion system will make the sound design more intuitive
and precise than it has ever been before in Counter Strike’s history.
This change is still in beta for now, but once it’s rolled out for real I’d expect
it to be forced on for all players to keep it fair and balanced. Occlusion does make
distant sounds quieter, especially if heard through surfaces, which will reduce what we
can expect to hear from where we are within the level. Not that this is a bad thing. I
think this update is a step in the right direction! It makes the audio more realistic, but only
in the good ways. Much like HRTF, I think we’ll soon take it for granted, but it will
have a small but positive effect on every round of CS:GO that’s played from now on,
especially on Nuke, which I’ll end this video with examples of. It’s a welcome improvement.

100 thoughts on “Sound Occlusion Analysed”

  1. Devil Zark says:

    occlusion should be off. i cant even hear where the shots come from

  2. DarkGharren says:

    HRTF just makes everything sound like it's underwater. They should've added proper surround sound instead.

  3. MrLeva115 says:

    Nice asmr video Philip

  4. Fjel says:

    Somewhere at Valve.
    Some pothead lead developer: ''Alright guys how can we fuck the game even more. We already fucked up gloves, sounds, pistols, we didn't even bother to do some theory crafting for the new de_dust2, we just slapped a new texture and made some minor differences, we didn't even thought about adding 128 tick matchmaking servers or unranked matchmaking option, and please don't get me started on that anti-cheat that is clearly not important for the game. So, any ideas?''
    Jeff: ''How about we don't fuck the game even further, and we listen to the demands of the community. Isn't the community the main body that sustains our game?''
    Pothead Dev: ''How About No!''
    Jack: ''How about fucking up the sound even more and then make everyone like it, even though they don't''
    Pothead Dev: ''Excellent, we`ll do just that''

  5. pixel says:

    After seeing this video (or should I say Hearing) I now know exactly when the CT's are having an SMG save round because I now know the exact MP9 sounds.

  6. Pijus Bartkevicius says:

    Anyone else who really freaking want it to change asap? or atleast be changable back to normal. Not only does it sound like shit (like every valves updates) but it makes it hard to play and it makes you lose fps. I don't understand how people like it, have they never tried the real audio settings? no hate but valve pls change… or half of ur players will quit <3

  7. Mr. Miss says:

    Finally an update that made me uninstall cs <3

  8. mundzuhaelter says:

    welcome to cs 1.6

  9. bitchslappedme says:

    your videos are always impressive

  10. TheBone2070 says:

    Where are the bulletcracks?

  11. NastEvo says:

    Valve needs to hire and pay you well my dude

  12. Nincadalop says:

    This sound technology is old news, but it still blows me away.

  13. Erelyes says:

    7,608 bullets were harmed in the making of this video

  14. Carloz Mizrachi says:

    So now you can perfectly understand from where the cheater is shooting you. Gj Valve, don't think about anti-cheat.

  15. Carl Rennie says:

    big lolz for the person who accidentally spectates your test server 😀

  16. ixRAZORxi says:

    It hurts my ears…

  17. wolakseak15 says:

    its shit….. i have cheap earphones for 5 eur. and playing on global elite vs other good gamers/hackers now i cant listen steps. need buy headset for 100eur. when i cant buy it .. i cant try to kill hackers etc cuz they know where im . and i dont know where they are. r.i.p cs go .

  18. outside7 says:

    Especially handy on nuke.

  19. MrCandystealer says:

    If you noclip out of bounds into the nothingless and spray you will kill every enemy on the map with a headshot.

  20. Wandi uk says:

    can you test 5.1 with new sounds please

  21. Max T says:

    i dont want the occlusion, and the command wont work unless sv_cheats is 1 -_-

  22. Darkpwnu says:

    Hey love your vids, curious about condemning in csgo, would like it if you made a general video about it. ty 😀

  23. Richard says:

    I can't play like this: I want the 5.1 back. I can't even use that anymore. I need help. It doesn't show up in the audio menu..

  24. MixLex says:

    so what do you recommend playing right now ?
    turning everything on ? Hrtf and Occlusion ?

  25. Smashen says:

    Does this give my teammates a headset to actually benefit from it?
    GoldNova4 speaking Hi 😀

  26. Dzyn says:

    anybody elses sound get fucked up and sounds underwater after the update? I can't even hear footsteps over the muffled gun sounds and everything is way quieter.

  27. Reese _ says:

    This needs to be in the main game for sure

  28. Wess says:

    Philip you have to apply for a job for Valve!

  29. Losi says:

    Your 3KLIKS discount code doesn't seem to work. Would definitely be nice to get that 20% off.

  30. Edgy Kid #42 says:

    includes paid promotion

  31. SDT says:

    The is a new Glicht on the new D2 called the Portal Glicht… How does that work? New Vid please

  32. Liam says:

    3Kliks could you please do a video on this video New 'Portal' Glitch on the New Dust 2! by fakejake

  33. OmegaPat says:

    JO 3kliksphilip, you need to look up the 'Portal' glitch, it has been found by fakejake on the new dust 2 map

  34. Alfredo Román Jordán says:

    I hate CsGo but I love your videos, they are so good

  35. Yalın Tümer says:

    +3kliksphilip Can you look at the new portal glitch found in dust 2?

  36. SOGINI12 says:

    csgo has uninstalled itself and now i have to wait 2 days with 90kbs 🙁

  37. aimcs1337 says:

    Hey Philip, can you investigate on the "Portal Glitch" on the new Dust2, that has been posted yesterday on Reddit?^^

  38. Henryzz says:

    On the New dust 2 you can move the bomb using the football. Like so he can see!!!!!!

  39. DannyXarn says:

    kliks, its possible to move the bomb with the soccer ball in dust2

  40. Smurfy McGee says:

    Great, now Valve force everyone to play in a fish tank after the new update.

    The HRTF update or whatever was fine, because it didn’t distort the sound, it just refined it. Occlusion makes my ears hurt, can’t play one game comfortably…

  41. The Unlucky Frog says:

    Philip check out the gamebreaking portal glitch by FakeJake. It's worth watching

  42. Jeremy Fox says:

    Dust 2 portal glitch

  43. matthew chang says:

    The new hole in new dust 2 near cat and top mid that u can basicly throw anything into the oblivion and not get it back, please so a video about it

  44. Robert Palm says:

    Investigate "portal glitch" please.

  45. Anthony Herbert says:

    Imagine if you could drop a Negev off cat walk (dust 2) and get a kill…

  46. Mr Soup says:

    do a video on the portal bug

  47. WrongLabel says:

    For some reason, I was randomly unsubscribed from you 🙁
    Resubbed though 🙂

  48. _GT_ says:

    I can hear footsteps at Inferno arch now? Bless.

  49. OneShot says:

    Teammates are always rendered… Only enemies are affected by the "Anti-cheat" …

  50. Yifang Wang says:

    How open "X O"?

  51. hobrev says:

    my problem with this update isnt that valve are trying new things or that the changes they made arent interesting and maybe better in future, once people get to terms with them, its the fact that its enabled by default and is kinda hard to disable. And in this update they didnt even have the massive 2 day open beta period they had with a few things in the past, where pros and content creators could have gotten used to the stuff at least for a bit. Valve seems extremely random at their development philosophy with csgo and it shows.

  52. Arif says:

    and meanwhile im hearing there was an update

  53. - Luiz says:

    I don't know how translated video titles work but the Brazilian Portuguese one is wrong.

  54. Maximum OverStat says:

    i think i know why the headshot sound plays, (just guessing) but it's probably because the bullets fly out of your head but are instantly ate by the void, so it plays the sound based on where they are on deletion (your head). (though as far as i know this could be completely wrong i haven't done any testing or anything).

  55. relativityIlldescried says:

    this is awesome, it makes it easier to tell if a gunshot happened in your LOS or not, effectively determining whether or not you're in danger from that particular shooter.

  56. Kharnix says:

    Please… do at elast 1 hour relaxing videos on diffetent maps of this. 4kliksphilip or something. cmon Q_Q

  57. Skye Smit says:

    Guess valve have to nerf the m4a1-s again..

  58. Lokader says:


  59. Talha Zahid says:

    144 dislikes ??? 1 must be from Guardian

  60. Renan Lira says:

    How can you hear sounds that are so far away from you? It doesn't work like this for me…

  61. valy0f says:

    The weapon sounds are still trash. Why cant be have the old ones back

  62. Chris Weeks says:

    Watched this on my monospeaker phone and pretended to understand

  63. 《 queueman 》 says:

    How to on it?

  64. Val D Mar says:

    Only God can reside in the void.

  65. haruga says:

    it was perfect before the updates on my actually decent headset. now it sounds like i have a headcold

  66. Alt+Doom says:

    Wall hacks for blind people.

  67. Geekenox says:

    Still waiting for 128 tick….

  68. PigsOnTheWings says:

    To be frank this is something that never needed a fix. Sounds were good and if you learned the quirks of the system you could locate whatever sound source you wanted. This occlusion shit sounds bad and whatever gear I plug into it (and I have a lot of it) it still sounds shit.

  69. TheBugError says:

    Only thing I hate about this is that sounds now sound so strange like not real when they are shot from behind a wall. If you dont know what I am talking about, well then try play office in competetive 😀 and you be like wtf I feel like I have something in my ears and I should clean them to hear better.

  70. Favoxhille says:

    i 100% agree with you, it makes the sounds much more intuitive and precise to spot the exact direction where they are coming from, the complaint from some pros like friberg is just stupid because you can still raise the volume to hear those muffled sounds louder but finally have a clear picture of where they coming from without having to rely on pure instinct/game sense

  71. Pedro Fleck says:

    Am I just drink or anyone else found funny an idiot running and shooting endless bullets everywhere?

  72. Da_Guy_With_Crocs says:

    firing a gun in a vacuum does not violate the laws of thermodynamics because in the bullet some air is still stored, allowing the gun to fire. Don't believe me? MythBusters did a episode where they actually tested it.

  73. 44kizza44 says:

    How do i disable this crap?

  74. Porta House says:

    Tori Black, Asa Akira, Remy Lacroix AND Rachel Starr. I'm sure I enter youTUBE.

  75. Olika120 says:

    quantum bullets.

  76. GameSquid says:


  77. Sarge says:

    how many more YT channels are you going to make for yourself? How many will be enuf?

  78. Panneer Gugan says:

    sorry for stupid question, but is it really true??? i mean dropping rare stuff on I was given a code @Babic probably it is still appropriate, hope so at least 🙂

  79. Invasion.- says:

    Tom Clancy's Counter Strike: Siege

  80. AshFung M says:

    Valve pls stop making this game realistic. It is supposed to be competitive only.

  81. T AH says:


  82. Caffine Molecule says:

    Too many videos with 2klicksphillip. He just doesn't have your quality of videos!

  83. matty boy says:

    I really love your videos phillip cos I'm a huge nerd and love learning about obscure game mechanics. I was wondering if you could do a video similar to this with Arma 3, exploring and testing out how sound works? That would be awesome. Anyway keep up the great work on your videos!

  84. Liam Duval says:

    What sound setting should I use for surround sound headphones? I heard you should use the “stereo headphones” option instead of “5.1 surround”

  85. FATAL_ERROR says:

    Even func_physbox's mass depends on applyed material (texture) and its volume

  86. sarah says:

    is it weird i could actually sleep to this csgo asmr

  87. over00lord Unknown says:

    1:49 So, anticheat doesn't send play location to prevent cheats (duh), but the server still sends the footsteps, and tells the client where the sound should be played at, meaning the cheats can just use THE FOOTSTEP SOUND POSITION… (duh)

  88. Venere says:

    3:37 that isn't a default texture is it?

    Philip are you hiding something?

  89. No0b says:

    the thingy with headshot is headshot aimbot it fixed in 2018 it works when you shoot somewhere near but not in the map it has to be the blak inky void thing

  90. Kapin says:

    This is the only video that has gave me actual ASMR…
    And I've seen actual videos about it, they don't do it lol

  91. Atomic Speed FT says:

    Forgot about this video…..

  92. Spooky says:

    youtube has surround sound encoders apparently

  93. Higgarn says:

    The sound in rainbowsix seige is sometimes extreamly hard to pinpoint the location the shots or steps are coming from. its so diffrent from what csgo is

  94. movax20h says:

    I really like attention to sound. This occlusion based attenuation and muffling, is really nice. It is obviously very far away from physical sound propagation modeling, but it does the job done very well in a lot of cases. And uses much less processing power and memory than full sound propagation modeling. My guess the way it works in this approximate model is in the name. It computes occlusions, in similar way we compute (ambient) occlusion in graphics. We shoot short distance rays from a source into all directions (30 directions would do the job) in space and limited distance (10 meters for example), if non of the rays hits anything, the source is not occluded. Similarly we do for destination of the sound (position of us), and separately take into account a distance, and what is directly between source and destination (aka weighted thickness of all barriers). With this 3 numbers, you can probably get enough accuracy and effects, to do volume adjustements and effects, to get reasonably good effects. And it is really cheap. You do not need to take into account echos, bounces, full level geometry, sound delays, etc., which would take probably 1000 more processing time. It can still be done on modern CPU or GPU, especially if you precalculate tables of all possible source-destination pairs (because in CSGO maps and environment are static, and there is essentially no things that move, like doors, vehicles, boxes, etc), but at the cost of memory.

  95. Lest Hodson says:

    Firing a gun in a vacuum doesn't "violate the laws of thermodynamics".

  96. Alex N says:

    Would be nice to have this in the best Source game ever – Left 4 Dead 2

  97. sarah says:

    i think the quantum headshots thing is actually you shooting yourself in the head because the bullets can't travel anywhere so they just end inside your head

  98. Occam'sGreatSword says:

    3kliks pointing out that sound ray tracing isnt a thing

  99. Alex Visan says:

    3kliksphilip shooting walls for 8 minutes

  100. Shallex says:

    i hate the sound of the nuke examples with occlusion off, it's just so unsettling to sound like it's right next to you when it's not. the occlusion makes it sound very realistic

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