Featured image of post The killer feature of modern HIFI playback system, "digital audio filter" takes you to swim in the ocean of sound

The killer feature of modern HIFI playback system, "digital audio filter" takes you to swim in the ocean of sound

Want to have a strong and perceivable change in playback system effects? "Digital audio filter" makes your HIFI system have the ability of "seventy-two changes"!

Getting to know digital audio filters

Owning a perfect audio playback system is the ultimate dream of all HIFI enthusiasts. In the era when the “analog audio system” was in power, humans did not have many easy-to-operate technical means to further improve the quality of audio works that have been recorded. The sound quality of a playback system is also limited by the sheer “capacity” of the hardware device. If you want to improve the sensory experience when listening to music, there is only one way to improve the hardware indicators.

However, with the continuous development of digital technology, when most audio works are digitally sampled and encoded into a specific digital audio format file, the idea of secondary quality improvement for the “produced” audio works become possible. This technology of “gene” editing for digital audio is called “digital audio filter”. If it is edited fast enough that the audio can be played back with little or no perceptible delay, then such technology is called “real-time digital audio filter” technology.

Well, the above introduction may not be very friendly to most people, and it is a bit obscure. So, what kind of technology is “digital audio filter”? What are the application scenarios in practice? All HIFI enthusiasts are invited to sit still again, and the big ship of HIFI knowledge will set sail again!

Wide application scenarios of digital audio filters

To introduce the technology of “digital audio filter” in a layman’s terms, we can use an analogy with a technology that is already known to most people and is very similar to it. That is a technology “video image filter” that has been used by many beauty lovers in recent years. I believe everyone knows very well that a portrait photo can make the person in it “beautiful” through digital means, which we call “image filter”. Its working principle is to use a special algorithm to automatically change the color of specific pixels in the image. The actual effect is similar to asking a “famous painter” to redraw your portrait to make it more beautiful. The effect of “video filter” is the same, but “video filter” has higher requirements on the processing speed of the hardware, requiring the hardware to calculate and redraw the image of each frame within a short delay, so that the images in the video People become beautiful.

Digitized audio streams have similar characteristics to photo-video and can also be edited. As long as there is corresponding algorithm support, theoretically any audio stream can be “beautified”. And it is worth mentioning that the origin of the technology of “digital audio filter” is much earlier than that of “image filter”. It’s just that in the early days of its birth, there was no very developed Internet, so not everyone had a deep understanding of it.

The application of “digital audio filter” is very extensive. According to its use, it can be roughly divided into several categories: “synthesis and splitting of audio channels”, “compensation for lossy digital audio”, “EQ regulator based on digital technology”, “spatialization of hearing sense” processing", “sharpening of hearing sense” and so on. The current mainstream digital audio filters can achieve the effect of real-time processing. In other words, most digital audio filters can be used by us to “listen to music”. Next, let’s introduce the details of each filter.

Synthesis and splitting of audio channels

This type of digital audio filter is mostly used in audio-visual power amplifier products. Audio-visual power amplifiers usually support the connection of multiple-channel speakers, but most audio-visual products on the market, such as CDs, DVDs, and Blu-ray discs, still use two-channel audio streams. In this case, a digital audio filter that supports channel splitting comes into play. It can further split the original two-channel audio stream into multiple audio streams with the same number of connected speakers, making Audio sources that do not originally support multi-channel are reborn in a multi-channel playback system. This technology is very practical in home theaters. For example, separate the applause of the audience at a concert and place it in the line output of two surround boxes, separate the voice of the singer and place it in the front and center output in the line. In this way, the advantages of the multi-channel speakers of the home theater are fully utilized, allowing users to obtain a more realistic sense of presence.

The processing behavior of this type of digital audio filter is also called “upmixing/UpMix”. The corresponding processing method is called “Downmix/DownMix”. The downmix audio processing filter is mainly used to resynthesize the multi-channel audio track in the original Blu-ray disc into a two-channel stereo sound track, so that HIFI enthusiasts who do not have a multi-channel playback system can normally play in a two-channel stereo playback system. Play back these audio-visual products and audio-visual programs.

At present, Dolby Laboratories in the United Kingdom and DTS Inc in the United States are well-known for developing audio track upmixing and downmixing digital audio filters. These commercial organizations usually license the technology to the manufacturers of major power amplifiers in the form of fee authorization.

Compensation for lossy digital audio

We all know that most audio files circulating on the Internet today are encoded with lossy digital audio coding standards. The digital audio filter can properly “restore” the audio files in these lossy formats, so that the audio quality of these lossy formats can be restored to a state closer to lossless. This type of digital audio filter analyzes the spectrum of a lossy audio file, and then predicts and compensates for the reduced audio portion. JetAudio, an old paid music player software that was once all the rage, is famous for this digital audio filter technology.

EQ regulator based on digital technology

HIFI enthusiasts should be most familiar with EQ regulators. Digital audio filters can digitally adjust the EQ of the audio stream. These digital audio filters are used in a wide variety of applications and can be found everywhere. As small as the music player hardware device or mobile phone operating system, as large as the PC desktop operating system or large audio debugging platform are the main battlefields of this type of digital audio filter technology.

Spatial processing of sense of hearing

This type of digital audio filter can achieve a corresponding transformation of the distance of a specific sound in the original audio stream from the listener through “genetic modification” of the audio stream. To put it simply, it is to let the listener feel that the source of each sound is separated from himself by a certain distance. The effect of these digital audio filters is especially noticeable when the listener is using headphones as the playback device. It can reduce the oppressive feeling caused by the earphones close to the ear, and at the same time, it can make the listener have the illusion of “distance” between multiple sound sources and himself, thereby increasing the layering of the sound and realizing the effect of “virtual surround sound”.

Hearing sharpening

This digital audio filter technology is primarily used to “sharp” the “human voice” in the audio data stream. Make the “vocal” easier to hear throughout the sound. If it is used in music playback, it will make the singer’s singing more prominent and easy to identify. It is usually very enjoyable to listen to songs dominated by female voices, and it is easier to hear the scale of the singer’s control over the emotion of the song. This technology is also used in some TVs. TVs with similar digital audio filter technology will have corresponding function on and off buttons in the audio adjustment option of the menu.

I want to use digital audio filters in my audio playback system, what should I do?

Having said so much, how do we use these digital audio filters in our own HIFI playback system? Don’t worry, the technology of digital audio filter does not exist only in theory, it is a technology that can be touched and experienced by every HIFI enthusiast.

All types of digital audio filters mentioned above have been made into real products. For example, some mobile phone manufacturers will build some digital audio filter sets in their mobile phones to increase the music playback experience of the mobile phone. Dolby Laboratories’ digital audio filter collection can be said to be the most used product by mobile phone manufacturers, and it is also a product with a high degree of commercialization. But many friends only know its existence, but they don’t know how powerful it is. Of course, the algorithm of digital audio filter is constantly improving, and the actual effect of the algorithm in different periods will be different. But it is undeniable that for mobile playback devices such as mobile phones, which are usually only equipped with small speaker “earbuds”, it is still necessary to be equipped with a decent collection of digital audio filters. Because the low-frequency output of earplugs is weaker than other large speakers, the most direct way to improve this situation is to “genetically modify” the audio stream through digital audio filters to increase the volume of low-frequency sounds. Once the amount of low frequency is pulled up, the overall sense of hearing will be closer to the effect of large speakers. One thing we need to pay special attention to is that digital audio filters can indeed increase the expressiveness of low frequencies or high frequencies, but the magnitude of the effect it produces is different in different playback devices. Devices with better raw expressiveness will also be more sensitive to digital audio filters, making it easier to hear the difference before and after using the filter.

Some friends may ask, why are these digital audio filter collections on mobile phones not sold separately? But they all appear in front of consumers in the way that the mobile phone comes with the factory. If sold separately, wouldn’t more people buy it? This is indeed the case, but it is a pity that these digital audio filters usually need to intercept the audio stream at the bottom of the operating system in order to “genetically modify” the sound. The action of intercepting audio stream data requires the support of the underlying interface of the mobile phone operating system. When designing the mobile phone operating system, for security reasons, it will not expose these important audio data interfaces to the application layer. To put it simply, the developer of the APP cannot make these digital audio filters work without the support of the operating system, but can only be pre-integrated in the operating system by the mobile phone manufacturer before the mobile phone leaves the factory. This is why some mobile phone players can add support for some audio filters by flashing their phones, but cannot add corresponding functions by installing some regular apps.

The above situation is only for mobile phones. For PCs, especially the Windows operating system, because the Windows operating system can increase the global audio filter support by installing drivers, major manufacturers on the Windows operating system have launched many digital audio products that consumers can purchase by themselves. filter products. For example, if you buy a sound card product of an innovative brand, you will get the THX or SBX sound effect function integrated in the innovative audio driver. These sound effect functions are actually a collection of digital audio filters. Let’s put it bluntly, if the sound card itself can’t let you hear the difference between the independent sound card and the integrated sound card, then THX and SBX can. In fact, many users who buy innovative sound cards go for THX and SBX. Compared with hardware sound cards, they are more interested in these digital audio filters, because these technologies are the key to making the sound change drastically. On the Windows operating system, there is also a category of digital audio filter products that are not bundled with hardware, and one of them has to be mentioned, that is FxSound. FxSound was officially announced as a free digital audio filter product at the beginning of this year, and it has always been a paid product before. If you want to try out the effects of digital audio filters for free, FxSound is worth a try.

Controversial issues of digital audio filter technology

At the end of this article, let’s answer a controversial question among HIFI enthusiasts. That is, will the digital audio filter make the sound dye or distort? To answer this question, let’s think about such a scenario. Suppose we each buy the same CD, but we all play it on different playback devices that we each own. So, will the actual effect of each of us play the same? Obviously not, because each of us has a different audio playback system hardware device. So in the end who plays out the effect is real?

During the production of music works or audio programs, the producers in the recording studio usually use the high-quality monitor headphones they wear as a benchmark to tune and synthesize various parts of the music or audio. In other words, only the sound from the headphone on the producer’s head is the most authentic feeling that the producer originally wanted to express to each listener. Any difference in the output capabilities of the high, mid, and low audio between the playback device we actually use and the headphones will cause distortion. Therefore, using digital audio filters to “gene edit” the audio that has been produced is not necessarily amplification and distortion. “Digital audio filters” are more about compensating for the lack of ambience of most playback devices, making these playbacks The equipment can better interpret the original artistic conception that the producer of the audio work wants to express.

Almost all digital audio filter products on sale will have preset gear options, such as “music gear”, “movie gear”, “game gear” and so on. These pre-adjusted gears are optimized configurations obtained through repeated tests on a large number of playback devices. In most playback devices, the advantages brought by digital audio filters can be better utilized to complement some of the playback devices. Not enough. Users only need to select the corresponding preset gear according to the type of audio they actually listen to, and then they can enjoy the sound effect improvement brought by the digital audio filter. These immediate sound effects are likely to be the “music exhilaration” you have been looking for for a long time.

Licensed under CC BY-NC-SA 4.0
Last updated on 2023-03-22 21:01 CCT
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