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Old 05-15-2019, 12:57 PM   #1
Join Date: Aug 2018
Default Hearing/Vision interaction and distance?

At what range does two parties see and hear one another and how do the two senses interact with one another and special actions (sneaking/etc)?

Consider the following cases:
  1. Two parties are walking through the woods normally, heading straight for each other; at what range does the winner of the Per/Observation/Hearing contest spot/hear the other party?
  2. One party is walking through the woods normally, someone else is sneaking up on them; should they even get a roll or should it be assumed they fail or should I do two separate tests (one normal skill and one vs contest)?
  3. What happens if the two parties both fail their rolls; how can I find a good compromise that they both end up closer?
  4. With Per/Observation for both sides, Stealth/Camouflage/Shadowing/etc being optional, as well as Hearing, how should they interact to produce intriguing situations of tension? For instance I wanna create situations like: "you hear someone walking about 10 yards away, but you can't see anything until a black shadow steps out and stabs you in the ribs".

I'd be inclined to use the range table (B550) for vision and the hearing table (B358) for hearing "inversely", but I'm not exactly sure how.

I'm thinking for vision, it might be better to roll separately for both (so just a normal roll if the other party doesn't sneak or anything and a vs contest if they do). The MoS can be converted to range from the Size column in the range table, but it'd probably need like a +5 mod to be realistic (so base would be 15 yards, for MoS 5). Also, apart from applying the vision modifier for terrain (that might be, say, 0 to -10) to the actual roll, it should probably limit the maximum to, for example, 10 minus the terrain modifier. So, in a forest with vision -5, a successful roll (including that same modifier) would mean spotting at 15 yards. and that is also the maximum (since 10 -5 = 5), but a failed roll of 1-5 means spotting at a shorter distance, while 6+ means basically walking into one another physically.

It'd be pretty nasty walking in a twisting cavern or dense jungle with -10, since then the max distance to actually spot stuff would be 2 yards... This would also make possible the rather comical happenstance where two stealthy party fail to spot one another (especially at night) to literally bump into one another! Well, barring successful Hearing rolls.

Also, I'm not sure if this makes vision too powerful, since you'd need to win by 6+ to get all the way up for a sneak attack or similar.

For hearing, I'm less certain, since sound can really vary a lot between environment, so for complete accuracy you'd need a "sound modifier" or separate table per terrain (which I think should be avoided). But as a start, I'm thinking of reading the MoS as the penalty to hear stuff. So if I roll a MoS of 5, while my opponent rolls Stealth at MoS 3, I'll hear his sneaking at 1. I guess you'd need to have some sort of "reflex" kicking in, so that tying or winning with 1-2 means avoiding that nasty backstab or whatever (at least a def at -2 for turning sideways, I'm thinking).

Anyone have any suggestions for this?
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Old 05-15-2019, 07:27 PM   #2
Join Date: Aug 2004
Location: Buffalo, New York
Default Re: Hearing/Vision interaction and distance?

It will take me some time to track it down, but I do believe there are specific rules regarding sounds and the distances they'd be heard. Might be in GURPS MYSTERIES or it might be some GURPS 3rd edition publication...

I'll see what I can dig up.
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Old 05-15-2019, 07:32 PM   #3
Join Date: Aug 2004
Location: Buffalo, New York
Default Re: Hearing/Vision interaction and distance?

Didn't take too long after all...

Page 48 of GURPS MYSTERIES has background information on sounds and the like. The rules generally utilize the speed/distance table, and modify rolls based on how much background noise there is (or isn't), along with any intervening obstacles and the like.
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Old 05-16-2019, 01:36 AM   #4
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Location: Kyïv, Ukraine
Default Re: Hearing/Vision interaction and distance?

I'd argue that Mysteries is disconnected from the way rest of GURPS handles things.

There are more modern takes that stick to the canon. High-Tech has the volume table that is Basic Set-compatible (doubling range per -1), and so does Enhanced Senses (page 21, while the next page handles hearing in tunnels).
Vicky 'Molokh', GURPS FAQ and uFAQ Keeper
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Old 05-16-2019, 10:07 AM   #5
Join Date: Aug 2018
Default Re: Hearing/Vision interaction and distance?

Thank you for the input. I never played any Mysteries, and my focus is mostly on fantasy, but I might take the chance to look it up more in detail at a later point.

Either way, I made some rules adjustments to RAW and my own thoughts, as below, along with some examples to explain my ideas:

Do a quick contest, with some modifiers to the spotter:
  • Standing still: spot +2
  • Combat/running: -5
  • Foe SM
  • Darkness penalties
  • Light in darkness: invert darkness penalty
  • Terrain visibility: -10 to 0
  • Alerted: +2
  • Looking in the right direction: +2 (but -2 elsewhere)

...and to observed (Stealth/Camouflage/etc):
  • Moving: Stealth -Move, walking -2xMove and no roll (just take -2xMove as the margin)
  • Standing: -5 if not actively hiding and no roll (just take -5 as the margin)
  • Time spent: if Camouflage
  • Actions while standing: ±0 to -5 (draw a bow ±0, casting spell with a dancing casting component -5)

If there is no active attempt to not be spotted, just apply the modifiers to the quick contest. The final margin of difference is capped at 10 +terrain, so for a forest which gives visibility -3, the highest result is 7. This margin is then looked up as range on the speed/range table.

This could also create moments of tension when the players are lying in ambush, and they have to decide how close on the range table they dare to go while the GM describes the situation (“the horsemen are about 15 yards away, continuing forward seemingly unknowing about the presence, when suddenly one of them reaches down into a saddle bag, 10 yards… and produces a wineskin”). The players can interrupt with an “I loose an arrow before the guard brings out his shield”, or even try a Body Language to judge if detected (vs Acting or similar if they really have been made).

It could also create moments of distracting guards and dashing from cover to cover, snatching the +5 relative bonus for going from Stealth to Camouflage, and work one’s way into a guarded area. However, anyone who is alerted gets +2, and looking in the right direction gives another +2 (but other directions suffer -2). I’d probably not re-roll this, but just use as it stands and go up/down levels from the initial rolls.

Also a quick contest, but with different modifiers for the listener:
  • Standing still: +2
  • Movement: -Move
  • Terrain acoustics: -10 to +10 (lush jungle with background noise to echoing cavern)
  • Sound: 0 to +10 (sometimes much more, for artillery/etc)
  • Alerted: +2

...and to the "listened" party (observe is to observed (n) as listen is to what (n)?):
  • Walking: -Move (not if sneaking actively; then it's covered by the roll)

If there's no attempt to avoid being heard, just apply relevant modifiers to the quick contest. The result is capped at 10 +terrain +sound. The final number is looked up in the speed/range table.

Hearing might also be subject to similar “gambling” of range as Vision.

Example 1 – Little John and his men ambush the Sheriff
In the Woods of Sher, a group of outlaws have hidden in the trees and plan to ambush the tax wagon and the guards of the local sheriff. The location is chosen opportunely at a lush place, where Vision is at -5, which also applies to the outlaws but they know where and when to look for a +2 to mitigate. It’s daytime (the tax collectors have refused overtime after normal office hours since a recent prison break incident), so no darkness. The forest has a -3 penalty to any sounds.

The outlaws have Camouflage 15 in the woods, and have taken some extra time to cut out footholds and such in the trees to sit in the most effective places, for an extra +2 (time spent). Their Vision and Hearing are both at 13, which both get +2 for being still in the trees, and another +2 for knowing where to look. The Sheriff’s men have Vision 12, but are at -2 to spot an ambush from above. Their horses and talking add +2 to the outlaws’ Hearing roll for the noise.

The horses are trudging through the forest, and the outlaws roll for their Hearing. They have 13 +2 +2 -3 for a total of 14. If they roll a 10, they get a positive score of 4. The horsemen have an automatic -5, for a total difference of 9, which translates into 70 yards (conveniently the maximum for -3 +2 = -1 in modifier). That doesn’t mean they understand what’s being said, but alerts them to their presence.

The Vision for the horsemen is 12 -2 -5 for a total of 5. Assuming a roll of 10, that a margin of -5. For the outlaws, their Camouflage is at 15 +2, and with a roll of 10 that’s a margin of 7, so a total of -12 for the horsemen, meaning they wont know what hit them.

The outlaws, on their side, roll to spot against 13 +2 +2 -5, and assuming 10 again, that’s a margin of 2, for a combined margin of 7. But, since the woods is at -5, the maximum is 5, and they will be spotted at 15 yards.

So, the result is that the outlaws can hear the horsemen approaching from 70 yards, see them from 15 yards, whereas the horsemen are completely oblivious until they get ambushed (as per normal ambush rules).
Example 2 – Camp ambushed by panther
During a dark evening in the jungle, a panther is streaking about looking for prey. It has caught the scent of peculiar yet delicious “two-leggers”, which it plans to look further into. The night has some stars and a moon, for a darkness of -5. The jungle itself has quite lush undergrowth as well, and also checks in at -5 for Vision, but -7 for Hearing because the jungle is teeming with life (mostly insects) even at night.

The panther has a Vision of 16. The panther is of course stalking, at Stealth 18, and doesn’t care about darkness. The prey has even lit a fire that makes their detection even easier! (Let’s ignore cat psychology about approaching fire for now.)

The campers have posted a single guard, who is vigilantly watching into the night every once in a while, and has Vision of 12, but hears slightly better – at 14. Their camp has no use of camouflage now that they lit a fire, but at least they are standing still for +2.

So, for Hearing, the campers roll against 14 -7 +2, and a roll of 10 means -1. The panther rolls vs Stealth 18, and with 10 that means a margin of 8, for a total comparison of -7 for the campers (ie virtually no distance).

But the campers might hear the danger, at 12 +2 -5 -5 for 4, so a roll of 10 means -6. The panther rolled a margin of 8, -5 for sneaking vs Vision, so the campers are even worse off for Vision, at -9!

The panther, for its part, doesn’t roll Hearing since the campers aren’t talking, but has Vision 16 -5 (basic undergrowth) +2 (alerted) +2 (knowing where to look), and ends up with a margin of 5 with a roll of 10. The campers don’t do anything, and simply have the basic penalty of -5, for a total of 10 in favor of the panther, which is capped at 5 for 15 yards.

Example 3 – Orc ambush in the cave
(I was going to try a last example here, of orcs rushing an ambush in an echoing cavern and not being disciplined to see how exactly conversation would affect things, and the party being alerted when rolling, but I didn’t have time for now so I thought I’d just post what I had)

This does kinda what I want, but I’m concerned about balance and exploits. It all does become a bit convoluted, almost, especially Hearing, but it might work, if a bit abstractly.

It’s seems rather easy to reach the cap of spotting, which is logical, in a way (no matter how good you are, those darn leaves are still in the way, but after that it’s relatively easy to see). I’d probably also let players choose a good location that would give them advantageous modifiers or their adversaries penalties, if they manage a Search roll or something.

Footnote: I find it much less difficult to explain high/low dice rolls, compared to the mid-range ones. If I put something at a roll of 10, I want to feel that “yeah, that is a plausible outcome IRL, too”, whereas when I assume 5 or 15, or even more extreme, it’s just “well, it’s a rand case, so something improbable must’ve happened”.

Any thoughts or tips are very welcome.

Last edited by FeiLin; 05-16-2019 at 11:18 PM.
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Old 05-16-2019, 12:57 PM   #6
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Hearing/Vision interaction and distance?

To be honest, the hearing rules are ridiculous; you won't lose any accuracy by switching it to use the range/speed chart.
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Old 05-16-2019, 01:06 PM   #7
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Default Re: Hearing/Vision interaction and distance?

Originally Posted by FeiLin View Post
…I made some rules adjustments to RAW and my own thoughts, as below, along with some examples to explain my ideas…
When one person is sneaking, I use a Quick Contest between Stealth and Perception and apply the results to the Size and Speed/Range Table [B550] to determine at what distance the stealthy person is seen and/or heard.

There is a full write up on my website. (You’ll need to click the “Stealth” switch towards the bottom of the page.)
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distance, hearing, perception, range, vision

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