Relative silence can do wonders.

To me, tension would be over-stimulated awareness of one's own presence and being. Maybe crescendo the cacophony of the BGz and effects and then suck it all out rapidly, resulting on only hearing breathing and maybe only 1 hyper-real sound of whatever action is being done (the bigger-than-life sound of tapping a pencil or tapping a foot on the ground, etc). Just choose one on-screen action and feature that in silence with an over-dramatic, hyper-real interpretation It can put the audience in a place of remembering our own feeling of tension where we have exited the ego of our mind and are left with observing our 'being' self almost as a 3rd person - aware of our breath and our every move as though we're being watched. Maybe leave it with a deep rumble under the near-silence because it's a non-direction frequency range and non-direction can be interpreted as tension (aka Interrogation room BGz).

I could be way off, but the way I understand it is when adrenaline is released, hearing sensitivity decreases a bit to protect itself. Our ears also compensate for the loss by focusing more attention on "peak" sounds, resulting in a sort of hyper-sensitive effect.

http://www.sciencedaily.com/releases/2010/05/100503111525.htm

My first thought was the literal tension of a taut rope on the edge of snapping. That slow, sporadic twitching of the rope being stretched by a weight, and maybe the occasional strands breaking.

For example, a rock climber, stuck on the side of a mountain, starts to hear the rope breaking. All other sounds drop out, even the ambiance, and we're left with silence, as others mentioned above. Layer that with the occasional, sudden stretches and snaps of the rope, and you've got a pretty tense moment!

Might be a little literal, but it's what I first thought of to "What does tension sound like"! :)

haven't read the other responses yet, but my thought is that when we become tense we tend to focus.

soncially, this would equate to total silence broken only by either one's own breath or some combination of ones own breath and the completely dry foley of the one thing that the person is manipulating.

Dropping everything to a dull background and then adding a tinnitus whine, which can be experienced naturally under stress.

http://www.tinnitustreatmentssite.com/tinnitusstress/

something that cuts through everything else? maybe a ticking clock or something else in a higher frequency realm that if you heard constantly for a lil will just stresses you out? if its rhythmic it could possibly simulate a clock and that time is running out.

i thought of the strings in psycho straight away, but they are more music

not a very creative answer though ahah

Hi Jay

  As previously mentioned I think manipulating BGs could be a great way to accent tension.

  Just as an example right now over here in the UK we’re experiencing quite a lot of trouble in the streets of certain places! I can imagine those places being very tense atmospheres right now.

Picturing myself in the middle of it all I can imagine hearing things like distant sirens, people (groups shouting), alarms going off, fire’s burning, water, dogs barking, crying, police helicopters, megaphones, metal groaning, car bys, wind.

  One scene that immediately springs to mind is in The Godfather. The restaurant scene with the train in the background. Helps develop the tension fantastically.

From a more physiological standpoint maybe accenting things like breaths and mouth noises/swallows could work? I know when I feel tense or nervous I dry up and it makes it harder to swallow lol Also sometimes when I’m feeling really under pressure people who are talking to me I might not really hear, as if they were being filtered out. Perhaps adding a similar effect to a bit of dialogue by filtering and pushing back with reverb/delay might achieve something similar.  

Hope that’s helpful   Andy

Another idea is an insistent and unrelenting sound. This doesn't necessarily mean that that sound has to be a foreground element. A sound that will not go away, and has some slight/slow movement to it (pitch change, volume change [crescendo's work more frequently than decrescendos], pan position, or even movement from background to foreground) can create tension in the viewer/listener.

It's a Gestalt thing, we want either good continuation or resolution. Good continuation would equate to a "natural" movement, while resolution obviously implies some sort of end or transition. Good continuation often leads into resolution, but "breaking" the Gestalt of either one in a sound causes unease in the listener. The two ends of the intensity spectrum for broken Gestalt results in tension (increasing/focusing attention) for slow and subtle (preparing for "fight or flight" response), and immediate attention (triggered "fight or flight" response) for fast and instantaneous.

There's been so many good answers, I don't know if I've come up with an original thought here. But I took a walk to the grocery store and came up with this short list.

• Incessant Repetition - "dad, dad, dad, dad, dad, Dad, DAd, DAD" I'd say this falls under the ticking clock, passing-time category

• Hyper Focus of the Mundane - With no context this seems awkward, but my thought was towards something like the squeak in the hinge of the wire cutters as our character picks the right wire to snip.

• Plywood Stress / Creak / Groan / Tear - Tension, under great stress, ready to snap

• Too Many Voices - Again with no context this one could just seem like a crowd, but thinking supporting character's voices sensibly overlapped to underscore the character's personal stake in failure.

• Squeaky Hinge / Break Drum - Pitched to that same brain-piercing octave of early tinnitus

• Balloon - Release the air through a pinched neck, reverse it. This goes under the rising pitch answer.

• Tea Kettle - Same rising pitch idea, but with that undertone of pressure

• Baby's / Child's Scream - Because we're wired for it

• Screw Gun - I'm thinking of that ratcheting sound a drill motor makes when you tighten a screw too far.

• Power Saw - Again rising pitch as it cuts through a long board, but with an edge of danger

• Bag Full of Groceries - The combination of cans, cardboard and plastic in my grocery bag made this great sound with all the contents under strain as I walked along. Made me think of being crunched under pressure, although that could've just been my mindset.

That was a good walk. Thanks Jay!

I think it would have to be a violin playing tremolo, maybe also rising in pitch.

I'm thinking may be something like a telephone ringing, its sounds stupid but I find it hard to resist while I'm doing something I can't just stay calm and just pick it up in my own time, I just feel the need to hurry and pick the damn thing, unless I'm in a bad mood and don't want to talk to who it is obviously. I don't know if its just me, I could be completely wrong though haha.

I like Mr. Spitz's idea. Frenetic motion into a hard cut hang. If you're about to be chased you could cut everything but the sound of a single piece of gravel under the chaser's shoe as he stares menacingly.

Basically pick one sound out of the everything that's going on and let it hang out over the otherwise silent void.

For me, complete silence with an ever ramping up "white noise" or subtle ambiance. If you've ever been in a place where it's so quiet, the white noise is deafening, that's the feeling I'd force artificially - not really that even "roar", but a few key frequencies accentuated.

Add to that some stilted breathing recorded in a VO booth, and you've got a nice claustrophobic, tense-sounding moment.

The classic dripping tap [though I'm not quite sure that'd find it's way into a studio/client context?]

But really, the most tense moments would be that suspense hung in the air moment of silence!

I'm late and many good answers have said what I couldn't so:

I would experiment with an electric guitar and a piece of metal or something to create some good scratching sounds which to me communicate tension and something about to be pushed past the breaking point.

Maybe some extremely loud screaming vocals or screams turned down to be barely audible under the foley or real-world sounds can create a nice subliminal bed for what you want to communicate.

Pulsating low-end. Sort of like when the dreams start collapsing in Inception.

High pitched frequencies 12.5K and above ramped up to an exaggerated volume after dropping out all other sound (sort of like silence, but with a tone - think opening scene of Children of Men).

What about something totally out there, like a rattle-snake rattle or cicada?

Don't forget this advice:

“Sometimes in the creativity area like sound, my instincts tell me to do one thing, but I do exactly the opposite and see what happens. For example, if you’re designing a scary weird creature, try putting in a high-pitched, low-level sound. Who knows, maybe that will be scarier.” Gary Rydstrom

Hope I could help.. Good luck!

Are we talking "experimental sound design" or "realistic" sound design?

If experimental as I understand it, check out ANY thriller, horror action trailer, it's full of this stuff. Very effective is anything that SLIDES up, or anything that accelerates.

Also add some high frequency stuff, jiggling around 10-12 Khz, almost inaudible, but it adds that extra stress. :)

Angelo Badalamenti's use of pure, stark silence during a tightening shot, or even during a seemingly mundane shot, is extremely powerful. It's a silence that you can hear, as if it creates a tangible vacuum of sound.

increase gain on room noise to crazy level?

Tension has no sound and is not a sound