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Cardboard使用空间音频(三)原文翻译

2016年09月17日 16:43:1210910

Spatial Audio

Introduction

The Google Virtual Reality (VR) SDK features a best-in-class audio rendering engine that is highly optimized for mobile VR. The goal of the engine is to give listeners a truly realistic spatial audio experience by replicating how sound waves interact with the environment and the listener's head and ears.

 

空间音频
介绍
谷歌的虚拟现实(VR)SDK特性最佳音频渲染引擎高度优化的移动虚拟现实。引擎的目的是给听众一个真正现实空间音频体验通过复制声波与环境交互和侦听器的头和耳朵。

How Spatial Audio works

Spatial Audio is a powerful tool that you can use to control user attention. You can present sounds from any direction to draw a listener's attention and give them cues on where to look next. But most importantly, Spatial Audio is essential for providing a believable VR experience. When VR users detect a mismatch between their senses, the illusion of being in another world breaks down.

The Google VR SDK simulates the main audio cues humans use to localize sounds:

Interaural time differences.

Interaural level differences.

Spectral filtering done by our outer ears.

空间音频是如何工作的
空间音频是一种强大的工具,您可以使用它们来控制用户的关注。你可以从任何方向呈现声音吸引听众的注意力,给他们暗示在接下来去哪里看。但最重要的是,空间音频提供可信的虚拟现实的体验至关重要。当虚拟现实用户检测他们的感官之间的不匹配,在另一个世界分解的假象。
谷歌VR SDK模拟主音频提示人类使用本地化的声音:
两耳的时间差异。
两耳的水平差异。
光谱过滤由外耳。

Interaural time differences: When a sound wave hits a person's head, it takes a different amount of time to reach the listener's left and right ears. This time difference varies depending on where the sound source is in relationship to the listener's head. The farther to the left or right side of the head the object is located, the larger this time difference is.

两耳时间差异:当一个声波撞击一个人的头,需要不同的时间到达听者的左和右耳朵。这时差变化取决于声源在关系到侦听器的头。越远的左边或者右边的头对象所在地,更大的区别。

Interaural level differences: For higher frequencies, humans are unable to discern the time of arrival of sound waves. When a sound source lies to one side of the head, the ear on the opposite side lies within the head's acoustic shadow. Above about 1.5 kHz, we mainly use level (volume) differences between our ears to tell which direction sounds are coming from.

Spectral filtering: Sounds coming from different directions bounce off the inside of the outer ears in different ways. The outer ears modify the sound's frequencies in unique ways depending on the direction of the sound. These changes in frequency are what humans use to determine the elevation of a sound source.

耳间水平差异:频率越高,人类都无法辨别声波的到达时间。当声源位于头部的一侧,另一侧的耳朵在头部的声影。约1.5 kHz以上,我们主要使用水平(体积)之间的差异我们的耳朵告诉声音是来自哪个方向。


光谱过滤:来自不同方向的声音反弹外耳的内部以不同的方式。外耳修改声音的频率以独特的方式取决于声音的方向。这些变化的频率是人类用来确定声源的高程。

Spatial Audio in Google VR

To simulate sound waves coming from virtual objects, we use a technology known as ambisonics to envelop the listener's head in a sphere of sound. The Google VR audio system surrounds the listener with a high number of virtual loudspeakers to reproduce sound waves coming from any direction in the listener's environment. The denser the array of virtual loudspeakers, the higher the accuracy of the synthesized sound waves.

在谷歌虚拟现实空间音频


模拟声波来自虚拟对象,我们使用一种技术称为ambisonics信封侦听器的声音在一个球体。谷歌VR音频系统围绕着侦听器与大量的虚拟扬声器繁殖声波来自任何方向的侦听器的环境。数组的密度虚拟扬声器,合成声波的准确性就越高。

Virtual loudspeakers are made possible through the use of head-related transfer functions (HRTFs). The cues discussed in the previous section are captured within these HRTFs. When audio is played through HRTFs over headphones, the listener is fooled into thinking the sound is located at a particular point in 3D space.

In the real world, as sound waves travel through the air, they bounce off of every surface in our environment, resulting in a complex mix of reflections. The Google VR SDK breaks this complex set of sound waves down into three components:

 

Direct sound

Early reflection

Late reverb

虚拟扬声器成为可能通过使用head-related转移函数(头)。在前一节中讨论的线索在这些头捕获。打了头在耳机音频时,听众是傻到以为声音位于某一特定点在3 d空间。

在现实世界中,当声波穿过空气,每一个在我们的环境中表面被弹开,导致一个复杂的混合反射。谷歌VR SDK将这组复杂的声波分为三部分:

直接的声音
早期反射
晚混响

The first wave that hits our ears is the direct sound which has travelled directly from the source to the listener. The farther a sound source is from the listener, the less energy it has resulting in a lower volume than closer sounds.

第一波袭击我们的耳朵是直接的声音直接从源到侦听器。越远的声源是倾听者,导致较低的更少的能量体积比听起来。

The first few reflected waves that arrive at your ears are known as the early reflections. These give the listener an impression of the size and shape of the room they are in. The Google VR SDK spatializes the early reflections in real time and then creates new, artificial sources for each of them.

最初几个反射波到达你的耳朵被称为早期的倒影。这些给听者的印象房间的大小和形状。谷歌VR SDK spatializes早期实时反射,然后创建新的人工来源。

Over time, the density of reflections arriving at your ears builds more and more until the individual waves are indistinguishable. This is what we refer to as the late reverb. The Google VR SDK has a powerful built-in reverb engine that can be used to very closely match the sound of real rooms. If you change the size of the room or the surface materials of the walls around you, the reverb engine reacts in real time and adjusts the sound waves to match the new conditions.

 

The Google VR audio system can also simulate the ways in which sound waves traveling between the source and listener are blocked by objects in between. The Google VR audio system simulates these occlusion effects by treating high and low frequency components differently, with high-frequencies being blocked more than low frequencies. This mimics what is happening in the real-world.

随着时间的推移,反射的密度到达耳朵构建越来越多,直到个体是没有区别的。这就是我们称为混响。谷歌VR SDK具有强大的内置混响引擎,可用于紧密匹配的声音真正的房间。如果你改变房间的大小或你周围的墙壁的表面材料,混响引擎实时反应和调整声波以匹配新的情况。

谷歌VR音频系统还可以模拟声波的源和侦听器被对象之间的旅行。谷歌的VR音频系统模拟这些闭塞效应治疗高和低频率成分不同,高频区被屏蔽比低频率。这模仿真实世界发生的事情。

Directivity

Closely related to the effect of occlusion is a sound object’s directivity pattern. A directivity pattern is a shape or pattern that describes the way in which sound emanates from a source in different directions. For example, if you walk in a circle around someone playing a guitar, it sounds much louder from the front (where the strings and sound hole are) than from behind. When you are behind, the body of the guitar and the person holding it occlude the sound coming from the strings.

随着时间的推移,反射的密度到达耳朵构建越来越多,直到个体是没有区别的。这就是我们称为混响。谷歌VR SDK具有强大的内置混响引擎,可用于紧密匹配的声音真正的房间。如果你改变房间的大小或表面
方向性

与阻塞的影响密切相关的是声音对象的指向性图案。一个方向性的模式是一种形状或模式,描述了声音的方式散发从源在不同的方向。举个例子,如果你走在一个圆圈周围有人弹吉他,听起来声音从前面和音孔(字符串)从后面。当你背后,吉他,拿着它的人的身体挡住来自琴弦的声音。

With the GVR audio system, a user can change the shape of a directivity pattern for an object and mimic the non-uniform ways in which real-world objects emit sound. There are two available parameters:

随着时间的推移,反射的密度到达耳朵构建越来越多,直到个体是没有区别的。这就是我们称为混响。谷歌VR SDK具有强大的内置混响引擎,可用于紧密匹配的声音真正的房间。如果你改变房间的大小或表面
GVR音频系统,用户可以改变对象的指向性图案的形状,模拟非均匀的方式真实世界的物体发出的声音。有两个可用的参数:

Alpha: Changes the shape of the sound emission pattern.

Sharpness: Controls how wide or narrow the emission pattern is.

Head movements and sound

By moving our heads, we can perceive the relative changes in all of the time level and frequency cues. This helps us to localize sounds more accurately.

α:声发射模式的形状变化。
清晰度:控制宽或窄的发射模式。
头部动作和声音
通过移动我们的头,我们可以把所有的时间和频率的相对变化的暗示。这有助于我们更准确地定位声音。

When a user moves his head in VR, his head-mounted display tracks the movements. The Google VR SDK uses rotation information to rotate sounds around inside the virtual loudspeaker array in the opposite direction of head movement. In this way, virtual sounds stay locked in position.

当用户移动他的头在虚拟现实,他头戴显示设备跟踪运动。谷歌VR SDK使用旋转信息在虚拟扬声器阵列内部旋转声音头运动的方向相反。通过这种方式,虚拟声音保持锁定的位置。

Design Tips

GVR Audio Room

For each part of your GVR experience, you should first determine if you need a GVR Audio Room. Audio Rooms provide early reflections and reverb, which help make the sound more realistic when there are nearby walls or structures. They are—not surprisingly—most useful when your scene takes place in an actual room. For outdoor scenes, an Audio Room can feel less natural, because you may have only one reflective surface (the ground).

You have full control over the amount of reverb and the material of the surfaces, so take care to match the room sound to the environment.

对于每个GVR经验的一部分,你应该首先确定你需要一个GVR音频的房间。音频房间提供早期反射和混响,使声音更现实当附近的墙壁或结构。他们不是时,多数有用你的场景发生在一个实际的房间。对于户外场景,一个音频的房间可以感觉不那么自然,因为你可能只有一个反射面(地面)。
你有完全控制混响的数量和材料的表面,所以照顾比赛房间的声音环境。

Atmospheric sounds

For producing the general ambience of a scene, like the wind in the trees, ocean waves, and birds, there are two choices for sound playback.

GVR Audio Sources.

GVR Audio Sources are the most flexible and work best for objects that move dynamically or that users might interact with. For example, if you attach an Audio Source to a bird, the listener hears the sound of the bird change naturally as it flies near, and then farther away. You can sprinkle Audio Sources throughout the environment to create the general ambience.

大气的声音


生产一个场景的氛围,就像风在树上,海浪,和鸟类,有两个选择声音回放。


GVR音频源。

GVR音频来源是最灵活和最适合动态移动的对象,或者,用户可能会相互作用。例如,如果您将一个音频源到一只鸟,听众听到鸟的声音改变自然,因为它附近的苍蝇,然后更远。您可以在音频资源在整个环境来创建氛围。

GVR SoundField Sources.

GVR SoundField Sources play back ambisonic files that let you hear audio from every direction. This is similar to how skybox or 360 photos work. Since ambisonic files only respond to head rotation, they work best as sounds in the distance.

GVR SoundField来源。


GVR SoundField回放ambisonic来源文件,让你听到声音从各个方向。这类似于天空体或360张照片是如何工作的。因为ambisonic文件只响应头旋转,他们在远处工作最好的声音。

Animate the sound source

If you want to command the listener's attention, but a sound source is out of view, you can animate the position of the sound. This enables the listener to pinpoint sounds much more quickly.

动画声音的来源
如果你想命令听众的注意力,但是一个声源的视图,您可以动画声音的位置。这使听者能够查明听起来更快。

Repeat the sound

To help the listener pinpoint a sound, play it more than once. This is why, for example, your phone's ringtone is not a single beep. If it was, you would have a hard time finding it, and you might not even be sure it was your phone. You can achieve the same effect by using sounds that comprise many distinct elements.

重复的声音

帮助听众查明一个声音,不止一次。这就是为什么,例如,你手机的铃声不是一个单一的哔哔声。如果是的话,你会很难找到它,你甚至可能不确定这是你的电话。你可以使用声音来达到同样的效果,包括许多不同的元素。

Use more complex sounds

 

You should avoid using overly quiet sounds, sounds lacking in high frequencies, or simple tones like a sine wave beep. Instead, craft sounds that have sufficient volume levels, are complex, and contain a full spectrum of frequencies.

使用更复杂的声音


您应该避免使用过于安静的声音,听起来缺乏高频率,或者简单的音调像一个正弦波哔哔声。相反,工艺的声音,有足够的音量水平,很复杂,包含一个全谱的频率。

Tips for crafting sounds

Audio Source sounds

For Audio Sources, make sure the sound files you use are monophonic and don't include reverb.

SoundField Source sounds (ambisonic sounds)

For SoundField Source sounds, we currently support first-order ambisonic files. These files are more complex than Audio Source files, and the tools and libraries that support them are still in the early stages.

With digital audio workstation (DAW) software and a plugin such as Ambix, you can create ambisonic files two ways:

Using monophonic files, place sounds on a virtual sphere around the user. You can move the sounds around and add effects to them.

小贴士制定的声音

音频源的声音

音频源,确保您使用的声音文件是单声部的,不包括混响。
SoundField来源的声音(ambisonic声音)
SoundField声音来源,我们目前支持一阶ambisonic文件。更复杂的音频源文件,这些文件和支持他们的工具和库还在早期阶段。
数字音频工作站(寒鸦)Ambix等软件和插件,您可以创建ambisonic文件两种方式:
使用单声部的文件,听起来在一个虚拟的领域用户的地方。你可以移动的声音和添加效果。

Use an ambisonic microphone like the SoundField ST450, TetraMic, or Zoom H2n to capture the sound of an environment in 3D. You can load the captured sound into the Ambix plugin and run effects on it, rotate it if needed, and then mix.

Check your work

After you get your VR experiences up and running, make sure to check your work. You want to ensure that what you see matches what you hear. For example, if you can hear the sound of ocean waves crashing, but the ocean looks frozen, it takes away from the sense of realism.

 

Be sure to visit all the places your users will go in your VR experience to confirm that everything sounds natural. In experiences where users can roam freely, they love putting their ear right up to sound sources.

使用一个ambisonic麦克风像SoundField ST450,TetraMic或变焦H2n捕捉3 d环境的声音。你可以捕获的声音加载到Ambix插件和运行效果,如果需要旋转,然后混合。
检查你的工作

VR启动和运行经验,后你一定要检查你的工作。你想确保你所看到的与你所听到的。例如,如果你可以听到海浪的声音崩溃,但海洋看起来冻结,远离现实的感觉。


一定要参观所有的地方你的用户将会在你的虚拟现实经验证实这一切听起来自然。在体验,用户可以自由行走,他们喜欢把他们的耳朵,声音来源。

Tom Merton/Getty Images

Take extra care to ensure that the sounds you're using are of high quality, are at a clear but comfortable volume, and adjust realistically with any movement. Because most of your users will be listening through headphones, make sure to test your sound on a variety of headphones, not laptops or desktop speakers.

汤姆·默顿/盖蒂图片社
听起来格外小心,确保你使用的是高质量的,在一个清晰但舒适的体积,并调整实际上与任何运动。因为大多数用户将通过耳机听,一定要测试你的声音在各种耳机,不是笔记本或桌面扬声器。

 

 

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