[MUD-Dev] Skotos Proximity System - a Technical Summary (LONG)

[Erik Jarvi]

Over all this is a cool idea. My comments are nitpicky, so take with a grain
of salt. I only took a quick look at my reference books, but you'll get the 
basic idea. (I hope!)  

On Mon, Apr 17, 2000 at 09:24:56PM -0700, Christopher Allen wrote:
<BIG snip>

> Proxes & Psycho-Acoustics
> =========================
> Psycho-acoustics is the study of how sounds are processed by the ear and 
> brain to give the listener useful information about the world outside. 
> The study of how sounds are localized by the brain, how pitch is 
> determined, and how we separate simultaneous similar sounds or pick 
> useful sounds out of a 'noisy' background are all part of psycho-
> acoustics.
> 
> In a sense this is the study of the 'subjective' perception of sound 
> properties. Important measures used in psycho-acoustics include 
> loudness, sharpness, fluctuation strength, pleasantness, and roughness.
> 
> Skotos uses some of the principles of psycho-acoustics to determine how 
> sounds work; it focuses on those factors associated with whether a sound 
> (usually speech) has been perceived, and whether it has been understood.
> 
> Psycho-acoustics are used by the SkotOS system, in conjunction with 
> proxes, to determine what can be heard and what can't. In particular:
>    * The subjective measure called 'son' is used to determine how likely 

In my reference books it's called sone.

>      it is that a sound will be noticed.
>    * Sounds from more distant proxes are subjectively more quiet.
>    * Ambient noise can decrease the intelligibility of sounds.
>    * Particular rooms or locales can increase or decrease ambient noise 
>      values.
> 
> 
> The Decibel & the Son
> ---------------------
> Various measures of sound and loudness are needed to determine the 
> audibility and intelligibility of speech.
> 
> The basic decibel (dB) is a logarithmic scale objectively measuring 
> sound intensity; a difference of 10 dB is a ratio of 10:1, and 3 dB is 
> about 2:1. The decibel scale is used because the ear responds to sound 
> in an approximately logarithmic fashion. Depending on the actual 
> frequency, most people will perceive a doubling in loudness for a dB 
> increase of 8 to 10.

Yes, for dB(watts) = 10 Log(P1/P2), but dB(SPL) = 20 Log(P1/P2).
SPL is Sound Pressure Level. 

> Subjective perceived loudness (as opposed to actual sound power) is 
> measured in sons; a 40 dB sound with a frequency of 1 kHz is 1 son, and 
> an increase of 10 dB doubles the son value. 

Why use sones?  Sones are frequency dependent. I'm sure you are aware
of the Fletcher-Munson curves.  Fletcher and Munson's theory is that 
human hearing does *not* have a flat frequency response. Are you going
calculate sones?  And how are you going to determine frequency?
Wouldn't it be much easier, but not 100% correct in the real world,
to just use dB's?  Jeez, I'd never thought I would say something like
that. :)  If you still want to use frequencies... why not use phons
instead of sones.  It maybe just a personal choice, but I'd rather
use round numbers than decimals.  I'd like to hear your reasoning, tho.

<snip about absorbsion>
> *Sample Loudness Levels, in sons:*
>    * 512     = jackhammer, air raid siren, percussion section of 
>                symphony, stock car race
>    * 1000    = prop engine plane at takeoff, un-muffled 50 HP engine 
>                fifty feet away
>    * 2000    = jet plane at takeoff, cannon (physical pain)
>    * 3000    = pistols and rifles
>    * 4000    = shotguns
>    * 5000    = rocket launch

<snip about speech sones>
      
Did you get these numbers out of a book or did you calculate them?
They seem AWFULLY high. I'm not an expert with phons and sones, but 
these numbers say that physical pain starts at 150 dB!  It's more like 
130dB or 512 sones, but no distance is given.

Heh I just thought of a funny weapon.  A ~140dB 14Hz sound. (It's umm
about the resonate frequency of a person's bladder. :)

> Proxes, Speech & Sons
> ---------------------
> Proximity affects how clearly things can be heard. In an average room 
> (ambient sound of 1 son) things are intelligible down to the level of a 
> soft whisper (1 x 1/4 son) for adjacent proxes.
> 
> Each additional category of proximity (nearby, vicinity, chamber, 
> bordering) increases the level of infallibility by approximately x4. 
> Thus the minimum intelligible level for nearby objects in a normal room 
> (1 son) is 1 son (1/4 x 4^1 x 1 son). Normal human conversation (4 sons) 
> can be heard in the vicinity (1/4 x 4^2 x 1 son). Quiet shouts (16 sons) 
> can be heard in the chamber (1/4 x 4^3 x 1 son). Screams can be heard in 
> bordering areas (1/4 x 4^4 x 1 son).

Indoors and Outdoors makes a big difference here. I'm assuming these are
indoors numbers.?
 
> Below these levels, words are increasingly garbled, down to the level of 
> inaudibility (a multiplier of x1/4). Thus the minimum level at which 
> something garbled can be heard in a near prox is 1/4 son. This 
> multiplier could be carried through all the categories: nearby 1 son; 
> vicinity 4 son; chamber 16 son; bordering 32 son.
> 
> Other activities can increase these levels, such as paying attention, 
> which is a x4 multiplier. Thus the absolute minimum level at which 
> something garbled can be heard by an attentive listener in a near prox 
> is 1/16 son. This multiplier could be carried through all the 
> categories: nearby 1/4 son; vicinity 1 son; chamber 8 son; bordering 16 
> son.

Cool!  I don't think many people would of thought of this.
 
> Ambient Noise
> -------------
> If there is too much ambient noise, whispers will fail or be garbled due 
> to the "din" of noise. With large amounts of ambient noise, even normal 
> speech may become garbled.
> 
> The default value for ambient sound is 1 son, as given in the example 
> above. However, objects, room details, and rooms themselves can have 
> intrinsic ambient noise levels. For instance, the area behind a 
> waterfall could have an ambient noise value of 8 sons.
> 
> Ambient noise is also a function of speech and the number of volitional 
> objects in a room, so being in the middle of a crowded bar or amidst a 
> herd of bison will be quite noisy.

Also transients.  So Bubba and Boffo are in a crowded bar, drinking a few
Dandelion wine spritzers, having a conversion at the bar, and someone nearby
<insert short annoying sound here>.  Will Bubba hear every word Boffo just said?
 
> Attenuation & Amplification of Sons in Proxes
> ---------------------------------------------
> Some objects, room details, and rooms may either attenuate (decrease all 
> sounds), absorb (decrease specific sounds), or even amplify (increase 
> all sounds) coming from a vicinity or chamber, or in some cases even 
> change how sounds that are adjacent are heard. 
> 
> For instance, while in a booth in the corner you will hear less of the 
> crowd outside, and they will hear less of you. If you are on a stage, 
> they will hear more of you, but you will hear less of them. 
> 
> Exits of a room may also attenuate or absorb sounds. They may do so in 
> different ways depending on if the exit is open or closed. This allows 
> for huge open city gates that stop few sounds, or a closed magical 
> portal that stops all sound. 
 
Again absorbsion is frequency dependant too.
 
> Open Issues with Proxes
> 
>    * Will people abuse the near proxes, thus requiring consent for all 
>      prox operations rather then just intimate ones? Is a "strongly
>      avoid" list required?

I'm guessing probably.
 
>    * Ambient noise may be not clear enough to players to be worth the 
>      trouble. Perhaps we should use a "din" marker rather than adjust 
>      the intelligibility of sound? If we do support intelligibility, 
>      what method do we wish to use to garble the speech?

Hmm that's a tough one to do well.  I always liked smaug's drunk
speech.  RoD is the only diku that I played extensively, so it could of
been in one of the predecers. 
 
>    * Should we have a paranoia flag that automatically puts everyone on 
>      your "avoid" list? 

Yes, newbies might be exploitable.
 
--
All music aspires to the condition of muzak.



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