Re: Dark Sense

From: simonh_at_msi-uk.com
Date: Fri, 07 Sep 2001 09:36:59 -0000


<dag.staalhandske_at_vastervik.mail.telia.com> says:

>Therefore you can think of each shout as a snapshot. If looking
>at something at a distance, the ultrasound must have time to travel
>to the object and back. 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.

That's not how dolphin sonar works. They encode a unique 'signature' into each pulse. They can transmit a continuous series of pulses and still recognise which pulse is which if they reflect back out of sequence. Artificial maritime sonar works the same way, and I think bats must as well, otherwise they wouldn't be able to operate in swarms.

>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.

They can use the doppler shift of a pulse from a moving object to determine it's approximate relative speed.

>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.

Dolphins can encode incredibly complex music-like sequences into each pulse of their sonar. They also listen to each other's 'ping', and reply with variations on each other's patterns. This is in addition to their 'song' which is at least partialy audible to us. We don't know why they do this, but there is definitely some sort of communication going on, with a potentialy very high ammount of data involved. That doesn't necesserily mean trolls can do the same thing, of course.

>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.

According to Trollpack, I thought the transmitter was in their snout.

>Can a troll move while using darksense?

Dolphins and bats move and manoeuvre extremely rapidly while using sonar. Admittedly water has different sound conducting properties than air, and bats may only use relatively short ranges, but then melee combat is fought at close range too.

Simon Hibbs


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