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VBR

VBR (variable bit rate) dynamic bit rate. That is, a bit rate is not fixed.

VBR

The audio encoding software immediately determines which bitrate to use based on the complexity of the audio data during encoding. This is an encoding method that is premised on quality and takes file size into account.
Table of Contents
1 Definition
dynamic bit rate
other meanings
2 differences
3 principles
4 Other acronyms
definition
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dynamic bit rate
VBR is also called dynamic bit rate encoding. Using this method, you can choose various transition levels from worst sound quality/maximum compression ratio to best sound quality/minimum compression ratio. When encoding the MP3 file, the program will try to preserve the quality of the entire selected file, the encoding will choose different bit rates suitable for different parts of the music file. The main advantage is that the sound quality of the entire song can approximately meet our quality requirements, but the disadvantage is that the compressed file size cannot be estimated during encoding.
Bitrate is the bitrate (speed) of the waveform [be careful not to confuse with sample rate, MP3 sample rate is generally 44.1 KHz and some higher ones are 48.0 KHz ], sound is naturally a waveform, that is, vibration. The vibration is drawn as an oscillating curve and the computer is on this curve when saved.
The best (highest) mp3 bitrate is 320 kbps (i.e. 320 kilobits per second), the waveform below 320 kbps will be corrupted and a lot of non-sharp detail will be lost (wave clipping) , while 320 kbps MP3 encoding mainly compresses treble details. Above 320 kbps, only a few programs support encoding, and the sound quality improvement is not obvious, so it is better to use lossless compression.
The higher the bitrate, the more accurate the waveform reproduction and the less distorted the sound. VBR is a technology that does not allow all music to take the same bit rate. The encoder determines the bit rate according to the complexity of the audio. Through dynamic adjustment, the music bitrate is high at complex places and the bitrate at simple places is low, so files of the same size will sound higher quality.
other meanings
VBR variable diameter gate (variable bore ram). Oil vocabulary in English (V1)
the difference
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For video, VBR is different from fixed bitrate mode, and its bitrate can vary with image complexity, so its encoding efficiency is relatively high, and there are few mosaics of fast-moving images. When compressing, the encoding software immediately determines which bitrate to use based on the video data, not only ensuring quality but also taking file size into account. In this way, the encoding program can choose from the worst video and audio quality (usually the highest compression ratio) to the best video and audio quality (usually the lowest compression ratio) among various video qualities. When encoding a video file, the encoding program tries to maintain the selected quality of the entire file by choosing different bit rates to encode different parts of the video file.

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Audio Coding Part5

VBR

About VBR

VBR Encoding

VBR: An interesting feature of MP3 files is that they can be read and played, which is also in line with the most basic features of streaming media. That is, the player can play without first reading the entire content of the file and play where it reads, even if the file is partially damaged. Although mp3 can have a file header, it is not very important for mp3 format files. Because of this feature, each frame of an MP3 file can have a separate average data rate without a special decoding scheme. That is why there is a technology called VBR (Variable bitrate, dynamic data rate), which allows each segment or even each frame of an MP3 file to have a separate bitrate, the advantage of this is that the sound quality is guaranteed to the maximum. . File size is limited. The advantages of this technology are obvious, but it is really difficult to use, because it requires the encoder to know how to assign the bitrate to each segment, which is like a dummy for encoders without waveform analysis. As such, VBR technology didn’t seem glamorous as soon as it appeared.
Experts have found that the human ear has a protective effect through long-term acoustic research. The sound signal is actually a type of energy wave, which propagates in air or other media. The most direct response of the human ear to the amount of sound energy, that is, the volume or pressure of the sound, is to hear the size of the sound. We call it the volume, which means the volume. The unit of energy is the decibel (dB). Even sounds of the same volume can be perceived by people as different in size due to their different frequencies. The 500 Hz frequency is most easily heard by the human ear. No matter whether the frequency is increased or decreased, even if the volume is the same, everyone will feel the sound become smaller. But when the volume drops to a certain level, the human ear cannot hear it, and each frequency has a different value.
You can see that this curve basically forms a V. When the frequency exceeds 15000 Hz, the human ear will feel that the sound is very small. Many people who are not very good at hearing cannot hear the frequency of 20000 Hz at all, no matter how loud it is… When the human ear hears two sounds with different frequencies and different volume at the same time, the one with the lower volume will also be ignored. For example, it is hard to hear the sound of the computer cooling fan during the day, but it becomes a noise source at night. According to this principle, the encoder can filter out many inaudible sounds to simplify information complexity and increase the compression ratio without significantly reducing sound quality. This shading is called the simultaneous shading effect. However, sound A is protected by sound B. If A is within the protection range centered on B, the protection will be more obvious. This range is called the critical bandwidth. The critical bandwidth of each frequency is different and the higher the frequency, the larger the critical bandwidth.
Frequency (Hz) Critical Bandwidth (Hz) Frequency (Hz) Critical Bandwidth (Hz)
Based on this effect, the experts designed a mental model of human hearing. After this model was imported into mp3 encoding, it led to a momentous revolution in sound quality. gradually eluted. At this point, the VBR technology, which has been buried for a long time, shines brightly, and with the use of the psychological model, it can perform powerful temptation and lethality.
For a long time, many people have a bad impression of MP3. More and more people think that the best sound quality of WMA is better than MP3. This statement is not correct. At medium and high bit rates, properly encoded MP3 is much better than WMA. It’s close to CD quality, with not-so-great hardware support, not many people can tell the difference between the two, it’s not a fairy tale, though you used to be able to easily tell the difference between MP3 and CD blindly. listening, but now cannot guarantee that it can distinguish correctly. Because MP3 is an excellent codec that was buried before.