Sound Suppression

[Sindri]

I find the way High-Tech handles sound suppression to be a little confusing.

Why is silent ammunition easier to hear than a light pistol with a maximum quality suppressor?

The way human produced sounds and weaponry compares on the table seems odd as well. An airgun is easier to hear than shouting while a crossbow is comparable to it and a bow is comparable to loud conversation. Unless I'm missing something that seems wrong, I can certainly hear loud conversation easier and farther than someone firing a bow.

Wiper suppressors seem rather poor in comparison to baffle suppressors. They don't last as long and reduce damage and range significantly. In exchange the pistol or SMG version is cheaper and weighs slightly less. The rifle version has an upside that PCs will actually care about by allowing higher max quality (though that lets it be as quiet as a max quality suppressor for a very light pistol or quieter than heavier pistols) at the cost of even worse damage and range reduction and no reduction in weight. I don't know if that's reasonable or if it's worth looking for an upside to make them better though.

While on the subject of suppression Mysteries pegs the limit of human hearing as -6 which is a pretty important addition to the hearing rules. Any opinions on that? Also Ultra-Tech of course has alternatives to conventional firearms and privacy field technology at TL 10 but how might it improve suppressors?

[vicky_molokh]

Mysteries seems to have a mind of its own that is staying somewhat away from the rest of GURPS, not very compatible.

Anyway, the human hearing limit seems to mean that a Per 10 Hearing +0 human is barely able to have a chance to hear this sound (makes sense - it's a roll against 4, or about 2%).

[Anthony]

The hearing rules are pretty broken in Basic; I'm not sure what the rules in Mysteries are, but they're probably broken too just in different ways.

On the topic of sound suppressors, it's entirely possible that a proper silencer, on subsonic ammunition, will perform better than silenced ammunition.

[Flyndaran]

One issue Gurps never deal with is how perceptive understanding is only a small subset of sensory detection .

[Anaraxes]

Originally Posted by Flyndaran

One issue Gurps never deal with is how perceptive understanding is only a small subset of sensory detection .

That's why Per is based on IQ, and not HT or a standalone stat.

[Varyon]

Originally Posted by Sindri

Why is silent ammunition easier to hear than a light pistol with a maximum quality suppressor?

Silent ammunition isn't subsonic, so there's still a sonic boom to contend with, but a light pistol is subsonic, and the suppressor basically does the same thing as silent ammunition would. You could argue silent ammunition should use the 16 yard line or function as a -4 suppressor, whichever is better.

Originally Posted by Sindri

The way human produced sounds and weaponry compares on the table seems odd as well. An airgun is easier to hear than shouting while a crossbow is comparable to it and a bow is comparable to loud conversation. Unless I'm missing something that seems wrong, I can certainly hear loud conversation easier and farther than someone firing a bow.

First off, a lot of hunting bows are actually silenced (Hearing -2), and these may be what you're used to hearing. That said, I strongly suspect the authors did their research when it comes to decibel levels of the various sounds listed, so they're probably in the right places. There are reasons why shouting and conversation are easier for most people to "hear" than other sounds at the same level. First, the noises people make tend to last longer - it's easier to notice a shouted sentence than a crossbow being fired. Secondly, I think our brains are geared to try to pick out and process speech, so we notice it much more readily. That is, the issue isn't so much hearing something (that is, the sound reaching our ears and being loud enough to register) as it is perceiving it (that is, actually realizing we just heard something other than background noise).

For the first, it might not be outlandish to use Time Spent. Any sound that lasts a second or less uses a normal Hearing roll, but beyond this every doubling of the time gives +1 to Hearing, probably to a maximum of +4 or so (at 16 seconds). For the second, a blanket +1 to Hearing for noticing people talking - provided they are the only ones talking - might work (although it's probably overstating things). Alternatively - and perhaps more realistically - this +1 (maybe even up to +2) can negate penalties for not paying attention (the Listener Distracted listing).

Originally Posted by Sindri

Wiper suppressors seem rather poor in comparison to baffle suppressors.

Baffle suppressors are good for general use. Wiper suppressors are a lot better in terms of silencing a shot, but do have the damage and range tradeoff. Wiper suppressors of all types should probably be allowed to go to -6, provided they don't drop things below 90 decibels.

Originally Posted by Sindri

While on the subject of suppression Mysteries pegs the limit of human hearing as -6 which is a pretty important addition to the hearing rules.

That puts an average human being able to hear someone sneaking around at a maximum of 16 yards, or hearing light traffic at 128 yards. That doesn't seem too bad. Note that only some penalties should apply hear, and having Acute Hearing should probably extend the needed penalty. For the former, background noise, distraction, lack of familiarity, and so forth shouldn't count, but range and sound reducers (terrain, ear coverings, suppressors, etc) should. That is, only penalties related to the sound actually reaching you (as opposed to you being able to notice it) should be counted here. For the latter, you need to have a -6 penalty after Acute Hearing has come into play - that is, with Acute Hearing 2, you'd need a total of -8 from range and sound reducing bits. Note that terrain that actually amplifies sound (like bare concrete) should probably function as Acute Hearing here. Unless you're going for harsh realism, I'd probably ignore the "-6 is silent" bit.

[Sindri]

Originally Posted by Anthony

On the topic of sound suppressors, it's entirely possible that a proper silencer, on subsonic ammunition, will perform better than silenced ammunition.

To me it seems like the best silent ammunition should beat the best silencer though. Silent ammunition is a much more radical design for eliminating noise so unless High-Tech is trying to say that it ended up being mostly pointless even within it's specific niche it seems like it should give a benefit aside from reducing bulk.

Originally Posted by Flyndaran

One issue Gurps never deal with is how perceptive understanding is only a small subset of sensory detection .

It does do a number of things to try to represent the difference between not perceived, perceived but disregarded and perceived and noticed. "Listener unfamiliar with firearms" for example gives a -4 to detect gunshots.

Originally Posted by Varyon

Silent ammunition isn't subsonic, so there's still a sonic boom to contend with, but a light pistol is subsonic, and the suppressor basically does the same thing as silent ammunition would. You could argue silent ammunition should use the 16 yard line or function as a -4 suppressor, whichever is better.

Originally Posted by HANS

No. Silent and Subsonic don't stack. The Silent rounds include the Subsonic feature.

Originally Posted by Varyon

First off, a lot of hunting bows are actually silenced (Hearing -2), and these may be what you're used to hearing. That said, I strongly suspect the authors did their research when it comes to decibel levels of the various sounds listed, so they're probably in the right places. There are reasons why shouting and conversation are easier for most people to "hear" than other sounds at the same level. First, the noises people make tend to last longer - it's easier to notice a shouted sentence than a crossbow being fired. Secondly, I think our brains are geared to try to pick out and process speech, so we notice it much more readily. That is, the issue isn't so much hearing something (that is, the sound reaching our ears and being loud enough to register) as it is perceiving it (that is, actually realizing we just heard something other than background noise).

No, I'm used to unsilenced bows. I'm sure the authors research is up to the usual high standard for GURPS books. I just don't really understand the final product. It makes sense to do something to help detection of continuous noise, though it shouldn't bring something past the human hearing limit of course. High-Tech says dB(A) is Decibel range at muzzle, weighted for human hearing which I assume handles some of the optimization of human hearing for human speech.

Originally Posted by Varyon

Baffle suppressors are good for general use. Wiper suppressors are a lot better in terms of silencing a shot, but do have the damage and range tradeoff. Wiper suppressors of all types should probably be allowed to go to -6, provided they don't drop things below 90 decibels.

That would do a lot to help wiper suppressors and remove some weirdness with the rile suppressor.

That puts an average human being able to hear someone sneaking around at a maximum of 16 yards, or hearing light traffic at 128 yards. That doesn't seem too bad. Note that only some penalties should apply hear, and having Acute Hearing should probably extend the needed penalty. For the former, background noise, distraction, lack of familiarity, and so forth shouldn't count, but range and sound reducers (terrain, ear coverings, suppressors, etc) should. That is, only penalties related to the sound actually reaching you (as opposed to you being able to notice it) should be counted here. For the latter, you need to have a -6 penalty after Acute Hearing has come into play - that is, with Acute Hearing 2, you'd need a total of -8 from range and sound reducing bits. Note that terrain that actually amplifies sound (like bare concrete) should probably function as Acute Hearing here. Unless you're going for harsh realism, I'd probably ignore the "-6 is silent" bit.

It makes sense to have Acute Hearing extend the penalty. On the other hand I'm not as sure about discounting background noise. One of the factors that produces "this is no longer meaningfully perceivable by human hearing" is interference by background noise.

[Varyon]

Originally Posted by HANS

No. Silent and Subsonic don't stack. The Silent rounds include the Subsonic feature.

I had thought this was the case initially, but looking at High Tech to answer the question I discovered Silent ammo doesn't include the drawbacks of Subsonic (namely, decreased damage and range), which implies it isn't subsonic. If it's meant to be, the drawbacks should also apply. Maybe something like -50 dB, to a minimum 90 dB (crossbow), might work?

Originally Posted by Sindri

High-Tech says dB(A) is Decibel range at muzzle, weighted for human hearing which I assume handles some of the optimization of human hearing for human speech.

As the table is intended for firearms, I strongly suspect any weighting is simply for how humans perceive gunshots, not necessarily how optimized we are for recognizing human speech.
EDIT: In fact, it might just be that they set the dB level based on how much noise they make in the frequencies we can hear.

Originally Posted by Sindri

It makes sense to have Acute Hearing extend the penalty. On the other hand I'm not as sure about discounting background noise. One of the factors that produces "this is no longer meaningfully perceivable by human hearing" is interference by background noise.

Not being able to perceive something solely due to background noise (assuming no actual destructive interference is going on) is a processing issue, not an issue in terms of raw human hearing. A character with high Per has high processing, and as you need a rather above-average Per to reliably hear things that are imposing a -6 or greater penalty anyway, this is pretty much a non-issue. As I said, the "-6 is silent to humans" bit should only apply to things that actually reduce your ability to hear them, rather than just reducing your ability to notice them.

[Sindri]

Originally Posted by Varyon

I had thought this was the case initially, but looking at High Tech to answer the question I discovered Silent ammo doesn't include the drawbacks of Subsonic (namely, decreased damage and range), which implies it isn't subsonic. If it's meant to be, the drawbacks should also apply. Maybe something like -50 dB, to a minimum 90 dB (crossbow), might work?

The actual numbers for silent ammunition that I've seen puts them at subsonic. Which is rather obviously what you would do if designing a firearm to be incredibly silent.

I don't know why High-Tech doesn't include all the features of subsonic if silent ammunition includes it or for that matter why it doesn't actually state that silent ammunition and subsonic ammunition or silencers can't be combined and sets silent ammunition at a particular line rather than using penalties like everything else.

If I were to guess I'd say that it's because silent ammunition is so ridiculously rare and such a significant design alternation that it was approached more as a detailing of the effects of the silent ammunition that actually exists than as a lens to turn ammunition into silent ammunition.

Originally Posted by Varyon

As the table is intended for firearms, I strongly suspect any weighting is simply for how humans perceive gunshots, not necessarily how optimized we are for recognizing human speech.
EDIT: In fact, it might just be that they set the dB level based on how much noise they make in the frequencies we can hear.

That would make sense. It makes the table a little awkward though since overwhelmingly what I want to know is how easily a human can perceive a sound.

Originally Posted by Varyon

Not being able to perceive something solely due to background noise (assuming no actual destructive interference is going on) is a processing issue, not an issue in terms of raw human hearing. A character with high Per has high processing, and as you need a rather above-average Per to reliably hear things that are imposing a -6 or greater penalty anyway, this is pretty much a non-issue. As I said, the "-6 is silent to humans" bit should only apply to things that actually reduce your ability to hear them, rather than just reducing your ability to notice them.

Destructive interference was what I had in mind. When something is incredibly difficult to make out background noise can not only make it hard to notice but actually destroy the information from the perspective of human hearing.

[Anthony]

Originally Posted by Varyon

I had thought this was the case initially, but looking at High Tech to answer the question I discovered Silent ammo doesn't include the drawbacks of Subsonic (namely, decreased damage and range), which implies it isn't subsonic.

Silent can only be realistically applied to ammunition that is already subsonic. There's no damage penalty for, say, subsonic .45 ammo, for the simple reason that it's subsonic as delivered from the factory.

Originally Posted by Varyon

Not being able to perceive something solely due to background noise (assuming no actual destructive interference is going on) is a processing issue, not an issue in terms of raw human hearing.

No, it's an issue of the raw sensor as well -- to put it in sensor terms, loud background means you have to turn down the gain on your microphone to avoid being deafened, which means you can't pick up as dim sounds. Even if you had sensors that were immune to that, S/N ratios place hard limits on what is theoretically possible to detect.