利用者:NeXyon/GSoC2011/3D Audio/3D Deviceのソースを表示

= Software 3D Device Design =

Here's the signal-flow graph of the audio data:

[[File:NeXyon_GSoC_2011_3d_audio_signal_flow_graph.png|640px]]

The calculations how they are done in the specific steps follow, dopper and distance calculation formulars are from the OpenAL 1.1 Specification, the others are derived by me, so might contain errors atm.

== Doppler ==

Input Variables:

* SP = Source Position
* SV = Source Velocity
* LP = Listener Position
* LV = Listener Velocity
* SS = Speed of Sound
* DF = Doppler Factor

Calculations:

<math> \vec{SL} = \vec{LP} - \vec{SP} </math>

<math> vls = \frac{\vec{SL} \cdot \vec{LV}}{|\vec{SL}|} </math>

<math> vss = \frac{\vec{SL} \cdot \vec{SV}}{|\vec{SL}|} </math>

Clamp vls and vss to a maximum of <math> \frac{SS}{DF} </math>

<math> pitch = \frac{SS - DF \cdot vls}{SS - DF \cdot vss} </math>

== Pitch ==

Input Variables:

* SP = Source Pitch

Calculations:

<math> pitch = SP </math>

== Distance ==

Input Variables:

* ref = Reference Distance
* rof = Rolloff Factor
* max = Maximum Distance
* SP = Source Position
* LP = Listener Position

Calculations:

<math> dist = |LP - SP| </math>

Here are three distance models possible with or without clamping.

In case of clamping:

<math> dist = max(min(max, dist), reference) </math>

Inverse Model:

<math> gain = \frac{ref}{ref + rof \cdot (dist - ref)} </math>

Linear Model:

<math> gain = 1- rof \cdot \frac{dist - ref}{max - ref} </math>

Exponential:

<math> gain = \left( \frac{dist}{ref} \right)^{-rof} </math>

== Cone ==

Input Variables:

* SZ = Lookat of the Source
* LP = Listener Position
* SP = Source Position
* in = Inner Cone Angle
* out = Outer Cone Angle
* og = Outer Cone Gain

Calculations:

<math> \vec{LS} = \vec{SP} - \vec{LP} </math>

<math> phi = arccos \left( \frac{\vec{SZ} \cdot \vec{LS}}{|\vec{SZ}| |\vec{LS}|} \right) </math>

<math> t = \frac{phi - in}{out - in} </math>

t is clamped between 0 and 1

<math> gain = 1 + t \cdot (out - 1) </math>

== Volume ==

Input Variables:

* SV = Source Volume

Calculations:

<math> gain = SV </math>

== 3D-Cue ==

Input Variables:

* S = Source Position
* N = Listener Up Vector
* C = Listener Position
* Z = Listener Look at Vector

Calculations:

<math> \vec{A} = \vec{S} + \frac{(\vec{C} - \vec{S}) \cdot \vec{N}}{\vec{N}^2} \cdot \vec{N} - \vec{C} </math>

<math> phi = arccos \left( \frac{\vec{Z}\vec{A}}{|\vec{Z}| |\vec{A}|} \right) \cdot sgn( (\vec{N} \times \vec{Z} ) \vec{A} ) </math>

phi is then used to decide which speakers the audio signal is played to.