噪音(Noise)。它就在我们身边。无论是哭闹的婴儿、空调的嗡嗡声还是办公室同事的活泼喋喋不休。一个安静的工作或放松的地方正在成为一种真正的优质商品。降噪(Noise)技术可以帮助将禅宗带回您的生活。
问题是，降噪是如何工作的？让我们回顾一下该技术的原理，以便您在购买自己的降噪设备时做出明智的选择。
一个（非常）基本的声音概述
声音是通过某种形式的物质以波的形式传播的能量。我们通常听到通过空气传播的声音。
例如，吉他弦在空气中振动，敲打空气分子。这些分子会撞到它们的邻居，等等。当在空气中移动的波击中您的耳鼓时，它会以与吉他(guitar)弦相同的频率移动它们。
您的大脑将这种运动转换为电信号，然后您将其视为声音。这是对什么是声音的非常简单的解释，但这是您了解降噪所需的最少知识。
A（非常）(Very)反声(Anti-sound)基本概述(Basic Overview)
波具有不同的属性。它有一个频率，即波经过一个完整周期的频率。
再次以我们的吉他弦为例。频率是琴弦在一次完整振动中移动的速度。我们将高频声音视为高音。低频声音更低音。除了频率，波也有振幅。那是波峰的高度。其次，波也有相位。这是波峰和波谷的位置。
如果您生成的声波振幅相同，但相位相反（波峰位于另一波的波谷处），则会导致相消干涉。这两个波基本上相互抵消。这可以大规模完成，您的抗噪声发生器中的能量需要与原始声音本身一样多。但是，如果你只想为一个人降噪，那根本不需要太多的电量，这就是降噪耳机的用武之地。
降噪耳机
降噪耳机是技术奇迹。在耳机的外部，有麦克风可以对耳机外部的环境噪音进行采样。这种声音由车载电子设备使用数学算法进行分析。每个耳机制造商都有自己的秘诀算法，所有这些算法的有效性都不同。
该算法用于计算破坏性干扰您所在的环境噪声所需的抗噪声波。然后，一种称为换能器的设备（本质上是一种扬声器）产生抗噪声波。
最终效果是，当您打开降噪功能时，您会突然陷入（近乎）寂静之中。这使您可以以更高的保真度欣赏音频，或者只是享受一些宁静。
主动和被动降噪(Noise)
我们刚刚描述的过程通常在产品规格表中被称为“主动降噪”或类似的东西。令人困惑(Confusingly)的是，一些耳机声称具有所谓的“被动”降噪功能。
不要混淆这两个功能是非常重要的。确实没有被动降噪之类的东西。这个术语的实际意思是，一副耳机的设计目的是使用普通的老式隔音装置来阻挡声音。
这意味着耳机的材料和设计在一定程度上将您与外界噪音隔离开来。从这个角度来看，把手指放在耳朵里也是“被动降噪”。
对于一副提供出色隔音效果的耳机来说，有很多话要说，但将其与降噪联系起来是一种营销手法。
主动(Active Noise Cancellation)降噪的局限性(Limitations)
目前(Current)的主动降噪技术无法完美阻隔噪音。当涉及到持续的、可预测的噪声源时，它们的效果非常好。想想(Think)喷气发动机、空调的嗡嗡声或冰箱压缩机的声音。现代(Modern)主动降噪非常擅长完全消除这种类型的声音。
相反，突然的不可预测的声音带来了更大的挑战。这通常包括大声的人类对话、有人打碎玻璃杯或算法没有时间分析的任何其他噪音。话虽如此，具有更快处理器和更复杂算法的新尖端系统也开始处理这些类型的噪声。
这种专门的主动降噪技术的一个有趣例子是在射击步枪、手枪和其他枪支时使用的电子耳罩。
这些耳罩使用被动隔音来阻挡所有声音，就像普通射击耳罩一样。但是，它们有外部麦克风，可以通过您周围的声音，以保持态势感知。因此，您可以轻松地与另一个人进行对话。但是，您周围所有声音的最大音量都保持在舒适的最大值以下。
这些系统通常可以提供定向声音并放大安静的声音，同时消除枪声。它与主流降噪耳机的技术并不完全相同，但密切相关。
人工智能驱动的降噪
一个相当新的发展是应用人工智能技术从音频信号中去除不需要的噪声。不幸的是，这还不能完全实时发生，因此它在消除噪音方面无效。它非常擅长的是从麦克风信号中去除噪音。
例如，如果您尝试在嘈杂的环境中与某人进行Skype通话或进行录音，那么另一端的人可能很难理解您在说什么。使用人工智能，可以分析该音频流，并且可以删除除您自己的声音之外的所有内容。
例如，Nvidia 的RTX Voice应用程序使用其RTX显卡中的特殊深度学习硬件来处理麦克风音频。因此，无论有人在键盘上打字、吸尘还是在做建筑工作，您的听众都听不到这些。您可以在这里看到这项令人难以置信的技术的演示。
由于在你对着麦克风说话和其他人听到音频之间有足够的时间让 AI 完成它的工作，因此在实时限制方面没有问题。也许随着技术的进步，这些超级有效的 AI 降噪方法也可以作为耳机降噪的一种形式。
降噪麦克风
从耳机开始，另一个类似技术对大多数人非常有用的地方，尤其是现在我们很多人都依赖远程工作，是降噪麦克风。
再一次，即使营销语言使用“降噪”一词，这些麦克风也不会产生干扰噪声源的抗噪声。相反，他们将声音作为一个整体，然后对其应用相同类型的噪声识别算法。在传递之前将其从输入音频流中删除。
您甚至可以获得内置AI 供电的(AI-powered)麦克风降噪解决方案，例如这款ASUS 适配器(ASUS adapter)。将其插入USB端口，将您的耳机连接到它，内部的小电子大脑将消除不需要的噪音，只留下您晶莹剔透的声音。
寂静的声音
你不会真正注意到现代生活中持续不断的噪音让你感到多么沮丧，直到你设法将它屏蔽掉。戴上一副好的降噪耳机，感觉就像一阵清风吹走了你的低级焦虑。
既然您知道降噪的工作原理，您就可以就您选择的降噪套件做出更明智的决定。如果你买对了东西，你会发现寂静的声音真的是你能得到的最好的音乐。
How Does Noise Cancellation Work?
Noise. It’s all aroυnd υs. Whether it’s a сrying babу, the hum of an air conditioner or thе аnіmated babble оf your office co-workers. A quiet place to wоrk or enjoy some relaxation is becoming a truly premium commodity. Noіse cаncellation technology cаn help bring the zen bаck іnto yoυr life.
The question is, how does noise cancellation work? Let’s go over the principles of the technology, so you can make an informed choice when buying your own noise-cancelling equipment.
A (Very) Basic Overview of Sound
Sound is energy travelling as a wave through some form of matter. We generally hear sound transmitted through the air.
For example, a guitar string vibrates in air, knocking air molecules about. Those molecules knock into their neighbors, and so on. When the wave moving through the air hits your ear drums, it moves them at the same frequency as the guitar string.
Your brain converts that movement into electrical signals that you then perceive as sound. That’s a very simplistic explanation of what sound is, but it’s the least you need to know to understand noise cancellation.
A (Very) Basic Overview of Anti-sound
A wave has different properties. It has a frequency, which is how often the wave goes through a full cycle.
Using our guitar string as an example again. The frequency is how quickly the string moves through one full vibration. We perceive higher frequency sound as high-pitched. Lower frequency sound is more bassy. Apart from frequency, waves also have amplitude. That’s the height of the wave’s peak. Next, the wave also has a phase. This is the position of the peaks and troughs of the wave.
If you generate a sound wave that has the same amplitude, but the opposite phase (the peaks are where the troughs of the other wave are), it causes destructive interference. The two waves essentially cancel each other out. This can be done at large scale, where you need to have just as much energy in your anti-noise generator as the original sound itself. However, if you only want to cancel noise for one person, you don’t need much power at all, which is where noise cancelling headphones come in.
Noise Cancelling Headphones
Noise cancelling headphones are technological marvels. On the outside of the headphones, there are microphones that sample the ambient noise outside the headphones. This sound is analyzed by onboard electronics, using a mathematical algorithm. Each headphone maker has its own secret-sauce algorithm, which all work to differing levels of effectiveness.
The algorithm is used to calculate the anti-noise wave needed to destructively interfere with the ambient noise where you are. Then a device known as a transducer, which is essentially a type of speaker, generates the anti-noise wave.
The end effect is that when you switch on the noise cancellation function, you’re suddenly enveloped in (near) silence. Which allows you to enjoy your audio at much better fidelity or just enjoy some peace and quiet.
Active and Passive Noise Cancellation
The process we just described is usually referred to on product specification sheets as “active noise cancellation” or something similar. Confusingly, some headphones claim to have something called “passive” noise cancellation.
It’s very important not to confuse these two features. There really isn’t such a thing as passive noise cancellation. What this term actually means is that a given pair of headphones were designed to block out sound using plain old soundproofing.
This means that the materials and design of the headphones isolate you from outside noise to some extent. From that point of view, sticking your fingers in your ears is also “passive noise cancellation”.
There’s much to be said for a pair of headphones that offer great sound isolation, but linking that to noise cancellation is a bit of marketing sleight of hand.
The Limitations of Active Noise Cancellation
Current active noise cancellation technology can’t block out noise perfectly. They work incredibly well when it comes to constant, predictable sources of noise. Think of a jet engine, the hum of an air conditioner or your fridge compressor. Modern active noise cancellation is incredibly good at erasing that type of sound completely.
Conversely, sudden unpredictable sounds pose much more of a challenge. This usually includes loud human conversations, someone breaking a glass cup or any other noise that the algorithm doesn’t have time to analyze. That being said, new cutting edge systems with faster processors and more sophisticated algorithms are beginning to deal with these types of noise as well.
One interesting example of such specialized active noise cancellation technology comes in the form of electronic earmuffs used when firing rifles, pistols and other firearms.
These earmuffs use passive sound isolation to block out all sound, just as regular shooting earmuffs do. However, they have external microphones that pass through sound around you, to maintain situational awareness. So you can have a conversation with another person with ease. However, the maximum volume of all sound around you is kept under a comfortable maximum.
These systems can often provide directional sound and amplify quiet sounds as well, while cancelling out gunshots. It’s not exactly the same technology as mainstream noise cancellation headphones, but it’s closely related.
AI-Powered Noise Removal
A fairly new development is the application of artificial intelligence technology to remove unwanted noise from an audio signal. Unfortunately this can’t quite happen in real time just yet, so it isn’t effective at noise cancellation. What it is very good at is removing noise from a microphone signal.
For example, if you’re trying to Skype someone or make a voice recording in a noisy environment, it can be hard for the person on the other end to understand what you’re saying. Using artificial intelligence, that audio stream can be analyzed and everything but your own voice can be removed.
For example, Nvidia’s RTX Voice application uses the special deep learning hardware in their RTX graphics cards to process microphone audio. So whether someone is typing on a keyboard, vacuuming the floor, or doing construction work, none of that will be audible to your audience. You can see a demonstration of this incredible technology here.
Since there’s enough time between where you speak into the microphone and the other person hears the audio for the AI to do it’s work, there’s no issue in terms of real time limitations. Perhaps with technological advancement these super-effective AI noise removal methods will work as a form of headphone noise cancellation as well.
Noise Cancelling Microphones
Moving on from headphones, another place where a similar technology can be very useful for most people, especially now that so many of us rely on remote work, are noise-cancelling microphones.
Once again, even though the marketing language uses the term “noise-cancelling”, these microphones don’t generate anti-noise to interfere with the source of the noise. Instead, they take the sound as a whole and then apply the same sort of noise-identifying algorithm to it. Removing it from the input audio stream before passing it on.
You even get in-line AI-powered microphone noise removal solutions, such as this ASUS adapter. Plug it into a USB port, connect your headset to it and the little electronic brain inside will remove unwanted noises, leaving only your crystal clear voice behind.
The Sound of Silence
You don’t really notice how much the constant noise of modern life grinds you down until you manage to block it out. Slipping on a pair of good noise-cancelling headphones can feel like a refreshing wind blowing away your low-level anxiety.
Now that you know how noise cancellation works, you can make more informed decisions about your anti-noise kit of choice. If you buy the right stuff, you’ll find that the sound of silence really is the best music you can get.
