What does spatial audio mean? 'Attachment: A comprehensive explanation of spatial audio technology'

php editor Xiaoxin will introduce to you today what spatial audio is. Spatial audio is an audio technology that can simulate real three-dimensional spatial effects in audio by using special encoding and decoding algorithms. This technology allows listeners to feel the distance, direction and environment of the sound source when listening to audio, enhancing the immersion and fidelity of the audio. In this comprehensive explanation of spatial audio technology, we will introduce the principles, applications and development trends of spatial audio in detail, so that everyone can have a deeper understanding of this field.

This week, Apple held its WWDC Global Developers Conference. After the conference, all media basically expressed disappointment. Firstly, no new hardware was released, and secondly, system updates were lackluster. The currently open beta versions of iOS 15 are basically software-level improvements, and Android users generally say they have used them many years ago.

Currently, the experience of cross-screen interaction between mobile phones, tablets and computers has not yet been realized, so its effect is not yet clear. However, recently, the Hongmeng system has brought this unprecedented effect in advance, which does not bring much shock to people.

If we want to find a bright spot in this developer conference, it is the widespread application of "spatial audio" technology. There are more music software or video software, as well as headphones and other hardware that support "spatial audio" technology, and this technology is constantly breaking through the circle and expanding towards the Android camp.

Today we will talk about “spatial audio”.

The term “Spatial Audio” was actually coined by Apple, and its essence is “computational audio.” Don't be intimidated by these noun concepts, it's very easy to understand.

Take the example of posting photos in the most common circle of friends in our lives. Nowadays, people who dare to post the original pictures directly without editing them are all Be a true warrior. Especially in group photos, if you don’t modify the other person a little bit, or just make yourself look beautiful, then the boat of friendship will capsize easily.

Some friends here may say that I don’t retouch the pictures. I just post them directly after taking them. But even so, the photos you posted are still edited. This is because computational vision is already an essential part of our mobile devices. When we take photos, the image processing system has already helped us sharpen the photos, improve the contrast, and make the sky bluer, the grass greener, and the people thinner.

Even if the photos we take are really authentic, on the display side, that is, on our screen, the picture will still be It has been beautified. Computational vision is so pervasive in order to create a feeling for us that is derived from reality but is more in line with human aesthetics than reality, even if the scene in front of us is not like this at all.

Compared with the rapid advancement of image technology, the sound seems too traditional. Except for so-called voice-changing software for entertainment and entertainment, computational audio technology has not found a suitable window for a long time.

Until noise-canceling headphones began to gain popularity rapidly, its principle was to capture environmental noise through the microphone on the headphones, and then emit an inverted sound wave inside the headphones to offset the environment. noise. This allows us to hear the sound in the headphones more clearly.

Now our mobile phones have widely applied this technology. With the development of computational audio technology, devices can also more accurately Recognize human voices and enhance only the human voice part to make our voice clearer during calls.

Some music software can now eliminate all the vocal part of a song and only keep the accompaniment, or on the contrary, keep only the vocal and remove the accompaniment. These are typical applications of computational audio technology.

Speaking of headphones, they have a fatal flaw, that is, they cannot create a sense of presence. In principle, our headphones can only achieve two-channel stereo sound, and will never be able to compete with the 5.1 or 7.1-channel sound surround effect in a theater.

The current panoramic sound theater allows the audience to clearly feel the sound effect of a plane flying overhead. How is this done?

Here I need to popularize another piece of knowledge, how our ears distinguish the direction of sound.

The reason why we can clearly judge which direction the sound is coming from is because we have two ears, and the sounds heard by the two ears are different, resulting in two differences. . One is called the time difference and the other is called the sound level difference.

To put it bluntly, the sound waves transmitted from a sound source will arrive at our two ears at slightly different times. In addition, because our heads block the sound, the sound waves coming from the left The sound volume on the side and right side will be different, and these two differences will be used by us to determine the direction of the sound.

If it is still difficult to judge, we will subconsciously tilt our heads. This action will artificially expand the time difference and sound level difference, which will help us make judgments.

The diameter of our head is about 20 centimeters, which translates into sound waves with a wavelength of about 1500Hz. Sound waves below 1500Hz have wavelengths larger than the diameter of our heads, so they can bypass our heads and the sounds that reach our two ears will feel the same. This is why low-frequency equipment such as subwoofers have no directivity and can theoretically be placed anywhere, because we cannot determine the direction of low-frequency sounds.

The question arises at this time, how do we judge the sounds above and below? Imagine that the time difference and sound level difference between sounds coming from 45 degrees above and 45 degrees below are exactly the same, but we can still judge it.

This is because we have auricles. There's a reason why our auricles grow into this weird shape instead of a smooth funnel shape. Sounds from above and below will produce different reflection effects in our auricles, and this difference will be keenly captured by us to judge the sounds from above and below.

Friends who are interested can do an experiment. Close your eyes and ask a friend to shake a bunch of keys vertically in front of you. , you will pinpoint the direction of the sound very accurately. But if you pinch the pinna, change their shape, or fill it in with plasticine, for example. Although the ears are not blocked, it is difficult for us to distinguish whether the sound comes from above or below.

The first thing that computational audio technology represented by spatial audio must achieve is to restore the ability of our ears to hear and distinguish sounds. Now when we put on headphones, no matter which direction the picture on the phone is, we always feel that the sound is coming from the front. This is actually counter-intuitive.

If there is a gyroscope in the headset, we can feel the shaking of our head, and computational audio technology can determine the relative position of our ears and the screen, and then adjust the position of our ears It can play sounds with different time differences and sound levels, and even simulate the effect of auricle reflection. This calculation will match the position of the mobile phone screen, making us mistakenly believe that the sound is always coming from the direction of the screen. Even if we hold the phone behind us, we will feel that the sound in the earphones is coming from behind. .

What are the benefits of doing this? This is the same feeling as when we watch a movie in a theater. The direction of the screen in the theater is always the main source of sound, and it will not change as our heads shake. This is also more in line with natural intuition. Each sound source is in its original position, and we are just in it.

Being able to achieve the x.1 channel effect with a pair of headphones was definitely an exaggeration in the past, but now, with the popularization of computational audio technology, this effect has really come to our ears.

Aren’t multi-channel traditional audio equipment going to be replaced?

No.

Being able to determine the direction of sound and being able to provide high-quality sound effects are two different things. Many people just want to enjoy music quietly and do not want to be disturbed by spatial audio technology. Compared with the current headphones that support spatial audio technology, the sound quality is still far behind the classic wired headphones at the same price. For film and television content, the sense of presence is often more important than sound quality, and spatial audio will play a greater role in this regard.

Of course, it also provides a more realistic VR experience.

Although based on algorithms, currently spatial audio still requires the cooperation of specific software and hardware. Headphones, video software and video content must support spatial audio at the same time in order to achieve the best results.

The wave of computational audio has arrived, and the world we hear will become both real and illusory.

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