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Wwise SDK 2023.1.8
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以下のセクションで、Spatial Audioがボイスグラフやバスグラフの信号フローにどう影響するのか、そして音の伝播モデルとどう関係するのかを説明します。
パスとコネクション
ランタイムにボイスやバスがほかのバスに接続する様子を、Wwise ProfilerのVoice GraphビューやVoice Inspectorビューで確認できます。Wwise Object同士をつなぐ電線のようなものを「コネクション」と呼んでいます。An Emitter-Listener pair is created whenever a voice or bus associated to a game object (an Emitter or a Room) is connected to a different game object (another Room, or the top-level Listener). Emitter-Listener pairs, which we will refer to as paths for the rest of this discussion, are used to compute attenuation curves, amongst other things. 1つのコネクションの中にあるパスの数は、0の場合もあれば、1つまたは複数の場合もあります。例えば、ゲーム側が AK::SoundEngine::SetMultiplePositions を使って1つのゲームオブジェクトに複数のポジションを設定すると、複数のパスが作成されます。Spatial Audioでは多数のパスが使われます。In the following discussion, we will examine the paths within each connection in the simple scenario where an Emitter is located in a Room, adjacent to that of the Listener, as illustrated by the signal graph below.
エミッタとリスナーの（直接）コネクション
The connection between the Emitter and Listener carries the dry (unreverberated) signal between the Emitter and the Listener. Spatial Audio creates a first path between the position of the Emitter and the position of the Listener to represent the sound wave that travels directly from the Emitter to the Listener. Its length is thus the distance between the two, and the Emitter's attenuation curves are evaluated based on that distance. Also, unless the Emitter and Listener have a direct line of sight, an additional Transmission Loss factor is added to this path: it is the maximum Transmission Loss found on the geometry in a straight line between the Emitter and Listener (or the maximum of both Rooms' Transmission Loss if there is no geometry). We call this path the direct path, or the transmission path, depending on whether it has a zero or non-zero Transmission Loss.
It's often possible for another sound wave to reach the Listener by means of diffraction, either through a Portal, or around the edges of geometry. This is a diffraction path. It bends around an edge, and its total length is thus longer than that of the transmission path. It does not have Transmission Loss, but instead it has diffraction, proportional to the angles by which it bends.
The following image of the Voice Inspector shows two paths on the Direct Connection: one for transmission and one for diffraction through a Portal.
下表は、この直接コネクションのパスの内容です。
| Path Type (Number) | Characteristics |
|---|---|
| Transmission/Line-of-sight (1) |
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| Diffraction (N) |
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 | 注釈: No delay is applied to the diffraction paths, even though the wavefronts taking those paths travel a longer distance and should thus arrive at the Listener later than those taking the transmission path. |
全てのパスが、1つの同じコネクションの中に納まっています。そこで、並行する音の伝播パスとして、とらえることができます。実際に、Master Audio BusにミキシングされるMarkers_Testの信号は、パスごとに別々にパンニングされて減衰します。ただしフィルタは1つのフィルタユニットで、そのカットオフ周波数は各パスの透過や回折で変動するフィルタ値と、その影響力に基づいています。
| 注釈: 本来、複数のパスが平行に存在することで、エネルギー節約の原則に反してはいけません。Spatial Audioは、この原則を重視し、パスのボリュームをノーマライズすることを避けます。ただし、サウンドエンジンのMulti-Directionパンニング方式を活用して、ボリュームのノーマライズと似た結果を達成しています。 |
エミッタとルームのコネクション
| エミッタ・ルーム間のコネクション |
| ルーム・リスナー間のコネクション |
The auxiliary connection of the Emitter towards a Room bus represents the energy injected by the source that reverberates inside the Room and produces a diffuse field. There is a connection to the Room that the Emitter occupies, and additional connections to each of the Rooms adjacent to the Emitter. The adjacent Room connections, and their send levels, represent the proportion of acoustic energy that propagates through those Portals into the adjacent Rooms. The remaining proportion is sent to the Emitter's Room.
The connection to the Emitter's own Room contains paths that are comparable to the Direct Connection. The first path is a straight line to the Listener with distance attenuation, as well as Transmission Loss if there is no line of sight between the Emitter and Listener. There are also diffraction paths, which are longer than direct / transmission paths, and have diffraction instead of transmission.
The additional connections to adjacent Rooms work the same way, except that the Portal that connects the Emitter's Room to the adjacent Room can introduce diffraction on the direct/transmission path: If an adjacent Room is not part of the shortest path from the Emitter's Room back to the listener, then diffuse energy exits the Room and "loops back" on trajectories perpendicular to the Portals' opening. Diffraction angles are computed from Portals' normal vectors if they have to bend to reach the Listener. (See Wet Path Diffraction)
ルームとリスナーのコネクション
The connection between a Room's bus and the Listener represents the Room's diffuse energy, simulated by the reverb Effect, propagating to the Listener. Unlike the previously discussed connections, filtering is applied "upstream", per sound, on the Emitter-Room connection, therefore although this connection does embed paths, they are only used for spatialization and Spread.
| 注釈: Auxiliary busses used in Spatial Audio to represent Rooms normalize their outputs across the number of outgoing connections from each bus. A Room bus with two outgoing connections, for example, often reports -6 dB in the Voice Graph when you select either of those outgoing connections. This normalization is not otherwise reported in the Contribution List. |
| 注釈: The model does not take into account further obstruction due to geometry outside the Room. そのようなジオメトリの影響は無視できる範囲とみなしています。 |
ウェット信号の距離に基づく減衰
The length of the paths introduced in the previous sections, which represent the propagation of a Room's diffuse energy to the Listener, cannot be defined exactly. このモデルでは、音が壁に向かって、その壁から別の壁に進む過程の、距離減衰は、完全にリバーブEffectで表現されているとみなします。Thus, a reasonable approximation of a path's origin would be the middle of the Room. However, a more satisfying result is obtained if the distance attenuation of the Room's diffuse energy depends on whether the source that excited it is located closer or farther from the Listener, especially if the Room is large.
さらに、現実世界の物理現象に反してWwiseでは音の距離減衰にカスタムカーブを使っています。In order to accurately compute the distance attenuation of the Room to the Listener, the Room should use the sound Emitter's attenuation curves. This poses a problem, because there can be multiple Emitters in a Room, each with its own position, and each with its own attenuation curve. Once all sounds within a Room have been downmixed and passed through a reverb Effect, it is impossible to selectively scale their volume based on their respective distance attenuation.
A brute-force solution to this problem would be to have a distinct bus and reverb effect for each sound within this Room. Since this would be prohibitively costly, Spatial Audio implements the following instead: The distance evaluation and attenuation, for the entirety of the distance between the Emitter and Listener, is applied on the connection between the Emitter and its immediate Room bus. 具体的には、ダウンミックスやリバーブの処理前に行います。これだと、バスに設定されている複数のEffectが直線的な位置関係にあれば、ソース1つに対してバスが1つ、リバーブが1つあるのと、同等の計算量です。一般的に、リバーブEffectはこれに該当します。
A similar principle applies to transmission and diffraction. In order for all parameters of a sound through Rooms to be customizable per-sound, those parameters are applied at the first connection between the Emitter and a Room. Every subsequent connection from Room to Room, or from a Room to the Listener are not filtered using these parameters. Assigning attenuation curves to a Room bus has no effect because they cannot be selectively applied to each sound in that Room.
エミッタ・ルームのコネクションとルーム・リスナーのコネクションを、もう一度考える
Attenuation, as well as Occlusion, Obstruction, Transmission Loss and Diffraction of the wet path is applied on the Emitter-Room connection, using the attenuation specified on the Emitter. Setting an attenuation on a Room bus will have no effect.
下表は、エミッタ・ルーム間コネクションのパスの内容です。
| Path Type (Number) | Characteristics |
|---|---|
| Transmission/Line-of-sight (1) |
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| Diffraction (N) |
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下表は、ルーム・リスナーコネクションのパスの内容です。
| Path Type (Number) | Characteristics |
|---|---|
| Transmission/Line-of-sight (1) |
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| Diffraction (N) |
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The following image shows both connections in the Voice Inspector. The highlighted section shows the paths in the Emitter-Room connection, where distance attenuation, Transmission Loss, and diffraction are applied. Paths embedded in the Room-Listener connection are not displayed here.
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| ルーム・リスナーコネクション |
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| エミッタ・ルーム間コネクション |
ルームをカップリングする
The connection between the Emitter's Room and the Listener's Room represents the diffuse energy of the Emitter's Room transferred into the Listener's Room and contributing to its diffuse energy. This transfer occurs through walls and open Portals.
Like the Room-Listener connection, paths are embedded here only for spatialization. Transmission, diffraction, and distance attenuation have already been applied at the Emitter-Room connection (see the discussion in ウェット信号の距離に基づく減衰).
| 注釈: If an open Portal exists, its propagation path will likely dominate the transmission path and enable coupling of both Rooms at full volume. The model does not try to modulate the transfer of energy based on the surface ratio of open Portals versus walls. 将来のリリースで改善される予定です。 |
| 注釈: The model assumes that geometry in the receiving Room does not interfere with the transfer of energy from the emitting Room. |
下表は、エミッタのルームから、リスナーのルームへのコネクションの、パスの内容です。
 | Tip: カップリングコネクションのボリュームをオフセットするには、オーサリングツールにあるGame-defined aux sendのVolumeを使います。This volume applies to a given Room bus towards all connected Rooms. |
リスナーとリスナーのルームの間のコネクション
This connection represents the diffuse energy of the Listener's Room that envelops the Listener. 距離による減衰はこのコネクションのインプット時にすでに考慮されているので、追加の減衰は適用されません。また、オブストラクションはなく、Spread値がほぼ100であると想定されています。