Audio Dynamic Range Compression: Limiting and Expansion


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Audio Dynamic Range Compression: Limiting and Expansion

Audio Dynamic Range Compression
Audio Dynamic Range Compression
Audio Dynamic Range Compression
Audio Dynamic Range Compression

Audio Compression: What It Is and How It Works

As an audio engineer, I’ve spent countless hours working with dynamic range compression. At its core, compression is a tool used to control the dynamic range of an audio signal. This means that it can be used to make quiet sounds louder and loud sounds quieter, resulting in a more consistent overall volume. Compression is an essential tool in the world of audio production, and it’s used in everything from music to film and television.
One of my favorite quotes about compression comes from the legendary producer Quincy Jones. He once said, “Compression is like a good pair of eyeglasses. You don’t notice them, but they make things look better.” And it’s true. When used correctly, compression can make an audio signal sound more polished and professional.

Dynamic Range Compression vs. Limiting

While compression and limiting are often used interchangeably, they are actually two different processes. Compression is used to control the dynamic range of an audio signal, while limiting is used to prevent the signal from exceeding a certain level. In other words, limiting is a more extreme form of compression.
One of the most common uses of limiting is in mastering, which is the final step in the audio production process. During mastering, the goal is to make sure that the audio sounds consistent across different playback systems. Limiting is used to prevent the audio from distorting or clipping when played back on a variety of systems.

Audio Expansion: The Other Side of the Coin

While compression and limiting are used to control the dynamic range of an audio signal, expansion is used to increase it. Expansion is the opposite of compression, and it’s used to make quiet sounds even quieter. This can be useful in situations where you want to bring out the details in a recording.
One of my favorite examples of the use of expansion comes from the film “No Country for Old Men.” In the film, there’s a scene where the main character is walking through a hotel room. As he walks, you can hear the sound of his footsteps echoing off the walls. The sound of the footsteps is very quiet, but it’s still audible. This is a great example of the use of expansion to bring out the details in a recording.
Final Words:
In conclusion, dynamic range compression, limiting, and expansion are all essential tools in the world of audio production. Whether you’re working on music, film, or television, understanding how to use these tools can make a huge difference in the final product. And while there are many different techniques and approaches to using compression, limiting, and expansion, the most important thing is to use your ears and trust your instincts.
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The compression algorithm of an Mp3.

The compression algorithm of an Mp3.

Mp3 compression algorithm

In addition to the physiological structural properties of the human ear, the function of the brain also plays a very important role.

Mp3 compression algorithm

The pitch in the sound is determined by the fundamental tone, while the timbre is determined by the harmonics, and the human brain will automatically complete the fundamental tone, even if the fundamental tone does not exist. For example, the bandwidth of a telephone is only 300~3200 Hz, but when we listen to a man with a base tone of 120 Hz talking on the telephone, we can still hear his correct tone and will not confuse a boy with a girl. . .

We still don’t know how the brain uses complex calculations to reconstruct this non-existent tone.

PS Add a little visual easter egg, can you see what’s weird about this image?

 

(Please read the answer to the end)

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_ Your vision~ amazing! The human body still has too many unknown magic eggs waiting to be excavated~~

The compression algorithm of an Mp3.

The compression algorithm of an Mp3.

Mp3 compression algorithm
Mp3 compression algorithm

The birth of the MP3 compression algorithm is nonsense of human organs in the digital age. The whole algorithm is not improved around the math, but rather optimized around how to fool the human hearing organ.

Mp3 compression algorithm
Mp3 compression algorithm

 

So this algorithm is very curious, Baidu finally found information after a long time, and has a little understanding of the principle of it, so please record it.

basic principle
There is a special effect of shading effect on the human hearing model.
The role of the cochlea is as a spectrum analyzer, converting sound waves into signals of different frequencies. The villous cells at each specific location will be stimulated by a specific frequency, but when the basilar membrane leads to fluctuations, the villous cells around it will also be stimulated. That is, if there is a frequency with a high volume, and at the same time there is a relatively weak frequency near it, the sound of the relatively weak frequency will be covered by the relatively loud sound, and our human ears have no way to distinguish the sound There is another sound of a weaker frequency.

To the human ear, the perception characteristics of sound do not change on a linear frequency scale (human hearing is not that good), but can be expressed in a series of limited frequency bands called critical frequency bands. Simply put, the entire frequency band is divided into several segments, and in each frequency band the auditory perception of the human ear is the same, that is, the psychoacoustic characteristics are the same.
Then, according to this principle, the mp3 compression work can be simply divided into two parts:

The first step: dividing the original audio data into several subcritical frequency bands according to certain principles;

Step 2: Analyze the frequency spectrum according to the psychoacoustic model to find the masking effect curve. Then, according to this curve, each sub-frequency band is quantized separately, and finally the compression of the audio is below the masking effect curve.

In this way, mp3 compression is done. And it is surprising that mp3 is really compressed in the digital world, but it belongs to compression without distortion for human perception.