Re: Darksense

From: Blatt Barry <bazblatt_at_cwcom.net>
Date: Fri, 7 Sep 2001 13:59:08 +0100


Interesting, but I would be inclined to look at what RW sonar using creatures like bats and dolphins do and how they use this sense.

>The basics

>From this description, it can be concluded that the troll gives out an
>ultrasonic signal that travels at speed of sound, normally around 340 >m/s
and hit objects. Some of the sound bounce back, some is >absorbed and some is transmitted and keep travelling inside the >object. The troll detects the echo, i.e. the sound that has bounced >back to it, and can draw conclusion from where the sound is coming >and how much time has elapsed. The sound the troll emits must be of >short duration or it will not be able to hear the echo.

Not necessarily so: Yes the sound on your own voice can give trouble in detecting incoming sound, but in the case of a beastie using sonar the brain will be able to adjust to block out the signal being emitted as another comes in. There is reason why they tend to use short pulses to do with the physics of wave propagation, but I can't remember what it is.

>For instance to look at an object a kilometre away you would need to >wait
6 seconds (2 times 1km divided by 340 meters per second >equals about 6 seconds). So in that case you see snapshots with 6 >seconds interval. Normally a troll emits ultrasound about once each >second. If rapid information is important, for instance in a melee, a >troll will shout ultrasound ten times per second, making himself >effectively blind to anything more than 17 metres away. Since the >image you get is a snapshot, the situation is equivalent to a human >watching something in stroboscopic light. In the strictest sense, a troll >can not "see" movement with his darksense. However he is very >good at detecting small difference between one picture and the next >and perceives that as a movement.

Yes, there is a delay for anything at a distance, but the movement sensing is very very good for bats at least - some species can pick a flying insect out of the air on the wing, something most vision using beasties would find a challenge. they do use the sounds emitted by their prey as a bit of help - buzzing in the insects thorax, the croaking of small nocturnal frogs etc.

As for what happens in a crowd - bats can find their way to a roost amid a flock of squeaking fellows without hitting any. They do have depth perception, can simultaneously focus on the cave wall, the bodies of their fellow bats, and pick out their own signal among the chaos of echoes being emitted and reflected by the rest of the flock. I would say a troll in combat is still well aware of what is happening behind his attackers and in the distance up to a good distance, or at least is as aware of such as any sighted creature.

>If a troll can hear a faint echo of the ultrasonic sound it emits, can he
>hear the ultrasound that other trolls emit?
>Yes and he can do so several kilometers away if conditions are >good. A
troll who is using his darksense signals his presence and >location to all trolls in a large area.

I would go further: Dolphins and other clever cetaceans emit a signal with a defnite coding that uniquely identifies that individual to its fellow school members. Not only will a troll know who is about over quite a distance, he will know their name as well, and by analysing the fequency and intensity of the signal will have an idea of what they are doing. (Hunting, close work, jsut wnadering about etc.)

>Therefore, in troll versus troll warfare, it is hard to achieve surprise by
>sneaking up on someone. What you do is to hide in a place, turn your
>darksense off and wait for the enemy to come. In tunnel warfare, the >enemy
usually does not have a great many ways of approaching you. >When the enemy comes, you will hear his darksense. If he chooses >to refrain completely from using the darksense he will have to move >slowly and clumsily and probably make enough normal, non->ultrasonic, noise for the ambushers to detect him. Scout trollkin are >fairly good at moving stealthily without using darksense. They are >therefore often used as point men.

I would give trolls a bit more ability to modify darksense than this. I would say they have the ability to tone down the sense to be able to see over a few meters, enough to walk, but without broadcasting over a wide area, a kind of sonic version of sneaking. They would still be very visible to other trolls darksense, but wouldn't give the game away immediately. You might even give especially canny trolls the ability to use the 'name signal' of another troll, deceiving the opposition into thinking they were a friend until they got close enough to recognise.

>Can this ultrasound be used for communication? A troll's ultrasound
>generator is not designed to be a speech organ. It cannot manipulate >the
ultrasound like a tongue and lips can manipulate normal sound. >Still, you could make a morse-like signal system with it, but no one >has bothered to do so yet.

Again, I would give them a bit more ability. Dolphins do 'talk' after a fashion using ultrasound. The bits we have managed to interpret seem to involve alarm signals vbased on the sonar reflection of well known objects. For example they will wanr eachother of sharks, by emitting a noise based on the sonar reflection of a shark. They also do a lot of other stuff we don't understand. I would give trolls the ability to send such basic alarms ultrasonically.

>How much information does a troll get from hearing another troll's
>ultrasound? He would know that another troll is present and where he >is.
If several trolls were present, he could count them as easily as a >human can count objects within sight. Trolls do not have distinct >ultrasound voices, so he cannot recognise individuals. He can >however, tell the race of the emitter and whether the emitter is >physically mature for his race. He can also tell how the emitter is >using his darksense. Few, extra loud shots with great intervals of >silence in between means that he is looking at something at a >distance, for instance.

As said above, I would give them their own voices, if only because it will be inevitable from the differences in structure of the meitting organ, in the same way as no two human voices will ever be exactly the same due to variations in the voicebox. In addition the variation in modulation that gives the distinctive voice is part of being able to differentaite your own signal from fellow beasties.

>Can a troll use another troll's ultrasound emissions to "see" the
>environment?
>In theory, yes. However, it is so difficult to decipher the information
>that the emitting troll must be standing very close to the listening troll
>and have the same physical orientation if this should work. This >method is
used if a troll has his ultrasound emitter damaged.

Probably right enough.

>If several troll's are using their darksense simultaneously, do they
>disturb one another?
>Yes. You cannot automatically tell if an echo is yours or another troll's.
>Therefore, they normally take turns emitting ultrasound and listening >to
the echo. This ultrasound etiquette is so natural for them that they >do so without thinking. In melee combat it is necessary to emit sound >several times per second. This becomes a problem if there are many >trolls in the same melee in the dark. An ultrasonic shouting match is >going on during the combat and everyone is having a hard time to >"see" very well. If a group of trolls were fighting someone who could >see well in darkness with another method than ultrasound, the trolls >would be at a great disadvantage. This could happen if Humakti, >whose swords give out light visible only to Humakti, were fighting >many trolls in the darkness. Still, trolls with darksense are at a great >disadvantage to most other beings who are blind in the darkness.

I would say not. As mentioned above crowds of bats manage very well not hitting ach other, I would say trolls do this as well.

>Can a troll deliberately "jam" another troll's darksense? Yes, by using
>his own ultrasound emitter he can make it very hard for another troll >to
see things close to the jamming troll. By doing so, he makes his >presence and location very clear to the troll being jammed, but the >jamming troll makes anything close to him or behind him so blurry it >is impossible to detect anything.

Anything this subtle would need magic IMO. The blocking troll would have to listen to all the incoming signals and emit a noise that exactly matched all of them peak for trough.

>Can a troll let the ultrasound bounce to see around corners the way a
>human could use a mirror for a similar purpose?
>In theory, yes. In reality it would require an extremely smooth surface,
>certainly not something you find in Uz caves, and some training to >use it
properly.

Agree. The Troll would have the same idea someone was coming as a human would, using ordinary level hearing. He would be able to tell if it was a troll coming by the randomish ultra sound squeakings , but little more.

>If a troll can see "inside" a living or dead body, would this be useful in
>medical diagnostics?
>In our world, it would be quite useful in the emergency room to be >able to
see broken bones, internal bleeding and sharpnel inside a >human body. In Glorantha, healing is done by magic and precise >diagnostics are not as useful as in our world. It would be very useful >to sort wounded people to make sure that those who needed quick >help fast where the ones who got it. It would also be useful in security. >With darksense you can do a complete body search, including a >cavity search of a person without touching a person.

Nice idea. You could have specially trained Xiola Umbar midwives with the ability to scan a pregnant troll, and special bodyguard trolls hired by human rulers to make sure no one sneaks a weapon into the throne room.

>Is darksense a 360 sense?
>Well hearing is a 360 sense, and darksense is a form of sending >out sound
and hearing the echo. However, assuming that the >ultrasound emits from the trolls mouth, it will send a stronger sound in >the forward direction than backwards. It is easier to hear someone if >he is facing you when he is talking. Therefore, the darksense is >significantly better in the direction the troll is facing, but it is fairly >good in all directions. You cannot sneak up on a troll from behind if >the troll is using his darksense. If you need to surprise a troll, you >need to hide nearby and wait for him to pass by close by.

I would make it far more tightly focussed. A bat has a hugely convoluted set of ears to get the direction right, and dolphins have an odd fatty structure on their foreheads to make the signal emission as focussed as possible (the ultimate in this is the head of the sperm whale, a huge sack of membranes, different density oils etc. that give them ultra sensitive long distance deep sea sonar).

>Can a troll move while using darksense?
>Ideally, the head should not move from the time ultrasound is emitted
>until the sound has bounced back. However, for normal troll >purposes, i.e.
walking or running in tunnels, this is not a problem. The >troll should just avoid moving turning the head rapidly. However, when >looking at something at a distance, standing still is required.

I would out no such limitation on it, bats and dolphins never stop. Treat it the same as normal human sight as far as distance goes.

>Do trolls turn off their darksense when they go to sleep?
>Yes.

>Will headgear "blindfold" darksense?
>I believe that ultrasound is easier to block out than normal sound.
>Therefore, a troll is less willing to wear headgear than a human. A
>troll's head protection is designed to leave the ears free and the troll
>only puts it on when he is walking into combat. A troll guard, for
>instance might have a helmet nearby, but until combat is imminent, >he will
not put it on.

A troll would design headgear that accomodates his darksense. He would certainly have his big ears hanging out of his helmet, and the rest depends on where you think the sound is emitted from. I would suggest the snout - bats can only ultrasound, and their voicebox is highly modfied to do so with only the lower register being at all audible to humans as a high pitched squeak. Dolphins make noises in their air holes along the same lines as a human burp, but are otherwise silent to humans.

So trolls would not use full helms, but only open helms with maybe a bar down the nose, and a canny opponenet will know that if he manages to bop one on the nose he will be blinded at least for a while.

>Can a troll's darksense see through mist or smoke?
>Yes.

But density of medium would affect the sight. Underwater I would guess they have as much trouble as people, not being adapted to it (though sea trolls who are would be pretty fearsome hunters, and might even be able to use sonar to stun prey in the same way a killer whales can), in the mountains they may have porblems as there are just too many faint reflections coming from all sides, the equivalent of mist.

>How do you hide from a troll's darksense?
>Try to make your silhouette contrast as little as possible from the
>environment. In a tunnel, lie on the floor, in the ceiling or stand against
>a wall. Very complex terrain with a great many complex surfaces like >a
forest is the best hiding place. Movement makes you easy to >detect against an unmoving background. However, movement in the >background will conceal your movement very well. So a forest with on >a windy day is the right place and time to sneak up on trolls. >Camouflage by choosing the right colours is not an issue, since trolls >are colour-blind with normal sight and darksense does not reveal >colours. Just avoid wearing white or very light colours in the darkness >since the trolls can see you with normal sight. As has been stated a >troll can "see" what is behind him and smoke or fog will not conceal >you.

Plain immobility won't help in my view. Trolls know the shape opf their own walls, and even in places they are unfamilar with a squidgy hollow thing like a living organism will stand out a mile. You still need something solid between you and the troll.

>Can a troll use darksense for prospecting? Yes, but I do not think
>ultrasound can travel very deep in the mountain, so the usefulness is
>limited.

They could tell a lot about how hard and friable a rock type is, and whether is is porous or not. This would be of some help with surface rocks, but nor more than the knowledge a human would use relating to colour, crystalinity and shape, fracture planes etc.

Barry Blatt (biology wonk)


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