Tag: mp3 player comparison

MP3 file format analysis


Free Download Mp4Gain
picture

MP3 file format analysis

MP3 file format analysis

MP3 encoding

MP3 file format analysis

Signal Description:

(1) MP3 encoding input signal: PCM (Pulse Code Modulation) sound signal, some audio files in .wav format are PCM signals.

( 2 ) MP3 encoded output signal: transmission in MP3 format

WAV format file capacity = (sampling frequency X quantization number of bits X channel) X time / 8 (byte = 8 bits). When the 2 bytes of 14H~15H have a value of 1 , it indicates the PCM encoding format of the data bit , which can be used as the input of the MP3 encoder .

3. Analysis of the SHINE program
SHINE is a MP coding program written in C language, consisting of 11 source files in total. Add the source file to the newly created VC purchase mode console application to run, but it must use command line mode when running.

 

1. File data structure
A config_t structure type is defined in types.h , and a global variable configuration is initialized with it, which is equivalent to an ” object ” in an object-oriented language, and is used to encode data and parameters throughout the process. coding Save and manage

Define a wave_t structure type to store PCM pulse format file information, and use wave_t to define the wave variable in config_t , which stores the MP3 encoded source information as the input to the MP3 encoder.

A type of structure mpeg_t is defined which is used to store MP3 encoded information, and the mpeg variable is defined in config_t with mpeg_t , and the information stored in this variable is output as MP3 encoded parameter information.

typedestruct {

time_tstart_time;

char*infile;

round_wave;

char* output file;

mpeg_tmpeg;

} config_t;

The above structure is mainly used to store the ” header ” information , and the byte stream entity information after encoding the output is stored in the bs structure ( defined in the bitstream.h file ), and the bs structure is defined as

static structure


Free Download Mp4Gain
picture


Mp4Gain Main Window
picture


Mp4Gain Features
picture


Free Download Mp4Gain
picture

MP3 file format analysis

MP3 file format analysis

MP3 file format analysis
MP3 file format analysis

1. Summary of MP3 and MPEG files

MP3 file format analysis
MP3 file format analysis

An MP3 file is made up of frames, and a frame is the smallest unit of an MP3 file. The full name of MP3 must be MPEG1 Layer-3 audio file.

MPEG (MovingPictureExperts Group), MPGE audio layer refers to the sound part of the MPGE file, which is divided into three layers based on the quality and complexity of the encoding, namely Layer-1, Layer2 and Layer3, corresponding to MP1, MP2 and MP3 format files.

2. Structure of MP3 files
MP3 files are divided into 3 parts : TAG_V2(ID3V2 ) , Frame, TAG_V1(ID3V1) .

( 1 ) Frame format

The frame header is 4 bytes and its structure is as follows

typedef FrameHeader

{

unsigned intsync: 11; // synchronization information

unsigned intversion: 2; // version

unsigned intlayer: 2; // layer

unsigned intprotection: 1; // CRC check

unsigned intbitrate: 4; // Bit rate

unsigned intfrequency: 2; // sample rate

unsigned intpadding: 1; // adjust frame length

unsigned intprivate: 1; // reserved word

unsigned intmode: 2; // channel mode

unsigned int mode extension: 2; // extended mode

unsigned intcopyright: 1; // Copyright

unsigned original: 1; // original logo

unsigned inemphasis: 2; // emphasis mode

}

HEADER, *LPHEADER;

Each frame takes 26 ms to play, regardless of the length of the frame. The length of MAIN_DATA is

Length(MAIN_DATA) = ((version == MPEG1)?144:72) * bitrate/frequency + padding;

( 2 ) ID3V1 format

ID3V1 is stored at the end of the MP3 file, a total of 128 Bytes, all information is stored sequentially and the insufficient part is filled with ‘\0’, which can be opened and viewed with UltraEdit.

typedef tagID3V1 structure

{

char header[3];

char Title[30];

artist char[30];

album char[30];

char Year[4];

char Comment[28];

coal reserve;

character track;;

charGenus;

}

ID3V1,*pID3V1;

( 3 ) ID3V2 format

ID3V2 is stored in the header of the MP3 file and consists of a tag header and several tag frames.

The tag header is 10 bytes,

char header[3];

char see;

character review;

char Flag;

character size [4];

Each tag frame consists of a 10-byte frame header and at least one byte of variable-length content. The frame header is defined as follows:

char frame ID[4];

character size [4];

char Flags[2];

How does an mp3 file work?

How does an mp3 file work?

How does an mp3 file work

What is the structure of an mp3?

How does an mp3 file work

An MP3 song has three
versions: 96 Kbps (96 kilobits per second), 128 Kbps and 192 Kbps. Kbps (bit rate), which indicates the amount of music data per second,
the higher the Kbps value, the better the sound quality, and the larger the file, the MP3 standard stipulates that an MP3 file with a constant bit rate is called CBR, and most of the
MP3 files are CBR, and MP3 file with changing bit rate is called VBR, and the length of each FRAME can be changed. The following are
the differences between CBR and VBR:
1) CBR: The size of the FRAME with a fixed bitrate is fixed (the formula is as above), as long as the total length of the file and the length of the frame are known, mp3 can be calculated from the 26ms needed to play each frame. The total playback time can also be monitored by counting the number of frames to control operations such as fast forward, fast rewind, and slow playback. Note: Sometimes not all frames are the same length and some frames may be one or more bytes longer.
2) VBR: VBR is an algorithm released by XING company, so there will be “XING” keyword in the MP3 FRAME (many popular
Small software can also perform VBR compression (it is not known if they comply with this agreement), it is stored in the first valid FRAME in the MP3 file and identifies that the MP3 file is VBR. At the same time, the first FRAME stores the total number of FRAMES of the MP3 file, which makes it easy to get the total playing time, and at the same time, there are 100 bytes to store the FRAME INDEX of 100 times segments of the total playing time. . Suppose a 4 minute MP3 song 240S is divided into 100 segments, and the time difference between two adjacent INDEXes is 2.4S, so through this INDEX as long as some FRAMES are processed before and then we can quickly find the FRAME header we need to fast forward. Table 2 Explanation of the byte of
structure of the first frame of the VBR 1-4 file The same standard sound frame header as CBR 5-40 Save the VBR file logo “Xing” (58 69 6E 67), the specific location of this logo depends on the adopted standard MPEG and the sound depends on the channel mode. The leading and trailing bytes of the flag are not used. 36-39 MPEG-1 and non-mono (common) 21-24 MPEG-1 and mono 21-24 MPEG-2 and non-mono 13-16 MPEG-2 and mono 41-44 Flags, indicates whether the frame number, Se stores information about file length, directory table, and VBR scale, and if so, 01 02 04 08. 45-48 frame number (including first frame) 49-52 file length 53-152 file table directory, used for byte positioning according to time. 153-156 VBR scale for bit rate changes

How does an mp3 file work?

How does an mp3 file work?

How does an mp3 file work
How does an mp3 file work

What is the structure of an mp3?

How does an mp3 file work
How does an mp3 file work

MP3 file is composed of frame (frame), frame is the smallest composition unit of MP3 file. MP3 full name should be MPEG1 Layer 3 audio files. MPEG
(Motion Picture Experts Group) translates into Chinese as Moving Picture Experts Group, and refers specifically to moving video and audio compression standards.
MPEG1 standard, also known as MPEG audio layer, which is divided into three layers based on compression quality and encoding complexity, namely,
Layer-1, Layer2 and Layer3, which correspond to the three sound files of MP1, MP2 and MP3 respectively, and use different
levels of audio files according to different purposes. The higher the MPEG audio encoding level, the more complex the encoder and the higher the compression ratio. The compression ratios of MP1 and MP2 are 4:1 and
6:1-8:1 respectively, while the compression ratio of MP3 is as high as 10:1-8:1. 12:1, meaning one minute of CD-quality music requires 10MB
of storage space without compression, but only about 1 MB after MP3 compression encoding. However, MP3 uses a lossy compression method for audio signals.

Low sound distortion, MP3 adopts “sensory coding technology”, that is, when encoding, the audio file is first analyzed for frequency spectrum, and then the noise level is filtered by a filter, and then each bit remaining is sparse and arranged by quantization, and finally form an MP3 file with a higher compression ratio, and make the file
compressed achieve a sound effect closer to the original sound source when played back.

2. The complete structure of the file
MP3 The MP3 file is roughly divided into three parts: TAG_V2 (ID3V2), Frame, TAG_V1 (ID3V1) ID3V2
contains
information like author, composer, album, etc. The length is not fixed, which expands the information volume of ID3V1.
frame
… Frame A series
of frames, the number is determined by the file size and the length of the frame
. The length of each FRAME may not be fixed, or it may be fixed. It is determined by the bit rate. Each FRAME is divided into two parts: frame header and data entity. The frame header records information such as bit rate, sample rate, and mp3 version, and each frame is independent of each other. ID3V1 contains information like author, composer, album, etc. ., and the length is 128BYTE. 3. MP3 Frame Format 1. Frame Header Format The frame header is 4 bytes long. For fixed bitrate MP3 files, the frame header format of all frames is the same. The data structure is as follows: typedef FrameHeader { unsigned int sync: 11; // unsigned synchronization information int version: 2; // version

lossless, lossy compression

lossless, lossy compression

lossless, lossy compression
lossless, lossy compression

Lossless compression and lossy compression are two types of digital image file compression.

lossless, lossy compression
lossless, lossy compression

1. Introduction
2 The principle of compression
lossy compression
lossless compression
3 advantages and disadvantages of compression

 

Introduction

Lossless compression is the compression of the file itself. Like other data file compression, it is to optimize the file’s data storage method. A certain algorithm is used to represent the repeated data information. The file can be fully restored without affecting the content of the file As far as the image is concerned, there will be no loss of image detail.
Lossy compression is a change in the image itself. When saving the image, more brightness information is retained and the color hue and purity information is merged with the surrounding pixels. The melting ratio is different and the compression ratio is also different. different The amount is reduced, so the compression ratio may be high and the image quality will be reduced accordingly.
compression principle

lossy compression
Lossy compression reduces the amount of space an image occupies in memory and on disk, and when viewed on screen, you won’t notice that it has a detrimental effect on the image’s appearance. Because human eyes are more sensitive to light, the effect of light on the scene is more important than the effect of color, which is the basic foundation of lossy compression technology.
lossless compression
The basic principle of lossless compression is that the same color information should only be saved once. The software that compresses the image first determines which areas of the image are the same and which are different. Images that include repetitive data (eg blue sky) can be compressed, only the beginning and end of the blue sky need to be recorded. But there can be different shades of blue, and the sky can sometimes be obscured by trees, mountains, or other objects, which must be recorded separately. Essentially, lossless compression methods eliminate some duplication and greatly reduce the size of the image that will be saved to disk. However, the lossless compression method does not reduce the memory consumption of the image, because when the image is read from disk, the software fills in the missing pixels with the appropriate color information. If you want to reduce the amount of memory an image occupies, you should use a lossy compression method.

pros and cons of compression

lossy compression
Lossy compression is characterized by maintaining gradual color changes and eliminating sudden color changes in the image. Numerous experiments in biology have shown that the human brain fills in missing colors with colors closest to the neighborhood. For example, for a white cloud against a blue sky background, lossy compression removes some of the color at the edges of the image scene. Looking at the image on the screen, the brain fills in the missing parts of the color with the colors it sees in the scene. By using lossy compression techniques, some data is intentionally deleted and the deleted data is never recovered.
It is true that the use of lossy compression techniques can greatly compress the data in a file, but at the expense of image quality. If the image using lossy compression is only displayed on the screen, it may not have much of an impact on the image quality, at least to the degree of recognition by the human eye. However, if an image that has been subjected to lossy compression techniques is printed on a high resolution printer, the quality of the image will be severely compromised.
lossless compression
The advantage of the lossless compression method is that the image quality can be preserved better, but the compression rate of this method is relatively low. However, if you need to print the image on a high-resolution printer, it’s best to use lossless compression. Almost all image files use their respective short-form names as file extensions. From the extension you can know what format the image is stored in, what software should be used to read/write, etc.

What is lossy and lossless audio?

What is lossy and lossless audio?

lossy and lossless
lossy and lossless

According to the sample rate and sample size of the sound, we can know that compared to the natural signal, the audio encoding can only be infinitely close at most, at least the current technology can only do this.

lossy and lossless
lossy and lossless

Compared with the natural signal, any digital audio coding scheme has certain advantages in that it cannot be fully restored.
In computer applications, PCM encoding can achieve the highest level of fidelity, which is widely used for material preservation and music appreciation. It is used on CDs, DVDs, and our common WAV files. Therefore, PCM has become lossless encoding by convention, because PCM represents the best level of fidelity in digital audio, it does not mean that PCM can guarantee the absolute fidelity of the signal, and PCM can only be infinitely close in the greater extent.
We usually include MP3 in the category of lossy audio encoding, which is relatively PCM encoding. The purpose of emphasizing the relativity of lossy and lossless encoding is to tell everyone that it’s hard to achieve true lossless, just like using numbers to express pi, no matter how high the precision is, it’s infinitely close, no actually equal to pi value.

The so-called lossy and lossless are relative to the software used for the audio format. According to the sample rate and sample size, it can be known that compared to the natural signal, the audio encoding can only be infinitely close at most, at least the current technology can only do this. Compared to the natural signal, any digital audio encoding scheme is lossy because it cannot be fully restored.
In computer applications, PCM encoding can achieve the highest level of fidelity, which is widely used for material preservation and music appreciation. It is used on CDs, DVDs, and our common WAV files. Therefore, PCM has become lossless encoding by convention, because PCM represents the best level of fidelity in digital audio, it does not mean that PCM can guarantee the absolute fidelity of the signal, and PCM can only be infinitely close in the greater extent.
We usually include MP3 in the category of lossy audio encoding, which is relatively PCM encoding. The purpose of emphasizing the relativity of lossy and lossless encoding is to tell everyone that it’s hard to achieve true lossless, just like using numbers to express pi, no matter how high the precision is, it’s infinitely close, no actually equal to pi value.

Lossy vs Lossless, understanding Audio Quality.

Lossy vs Lossless, understanding Audio Quality.

Lossy vs Lossless

Why the mp3 arises and becomes a success?

Lossy vs Lossless
Lossy vs Lossless

We talked in a previous article about why it was urgently needed when the internet started to find a way to compress the audio, since even thinking about transferring from one computer to another and storing an entire CD of music there was a feat that almost nobody could do. , much less online.

Fraunhoffer, who developed the mp3, mixed both theories:

1.- Compress using classic compression techniques, zip type.

2.- Use the extensive knowledge about human hearing to be able to rule out everything that the ear does not perceive.

Just as we have read that some animals see colors differently from human beings or even can see better in the dark… In the same way, the special and particular hearing of human beings has developed not in function of listening to music. .. or at least not in listening to it in high fidelity, but rather it is related more to our survival, to language, etc.

We know what the limits of human hearing are, we do not hear sounds lower or higher than certain perfectly known points.

There are whistles that dogs hear and humans don’t.

Would it make any sense to occupy more space on the hard drive to save, for example, frequencies that humans cannot hear?

The extreme purists may be exaggerating if they dream that the audio file does not drop any frequencies, but tests and trials have shown that an mp3 with a bitrate of 196 khz and a samplerate of 44100 or higher are practically indistinguishable from the uncompressed original for 99,999 people. of every 100 thousand.
Put another way, only one in a hundred thousand people can tell any small difference between a slightly above-average quality mp3 and the uncompressed original.

Mp4Gain is, without a doubt, the best option when looking to normalize the volume to make an mp3 or any other audio or video file achieve the most suitable loudness (see the list of files that Mp4Gain supports)

How MP3 Players Work

How MP3 Players Work

mp3 player

The MP3 player is the latest in the evolution of music formats that help consumers enjoy music.

Mp3 Player

Records, eight-track tapes, cassettes, and CDs – none of these music formats provided the convenience and control that MP3 players did before. With an MP3 player in their hand or pocket, consumers can create personalized playlists and take thousands of songs with them.

they go.

All the stored music and the MP3 player itself can fit in a single device that, in some cases, weighs less than an ounce. Portability is a major factor in the popularity of MP3 CD players and CD storage cases. In addition, some devices offer additional technology, such as video and photo viewing, alarm and calendar functions, and even cell phone and Internet services.

In this article, you will learn more about the technology behind MP3 players and the different types of players available. You can also find out how to get the melodies and how to use the accessories for your player. Get started by learning the MP3 file format on the next page.

content
The MP3 file format
this technology
Types of MP3 Players
fill your playlist
Accessories Your MP3 Player
The MP3 file format

The MP3 file format for music made its debut in the late 1990s, a file-sharing service, and the first portable MP3 players. MP3, or MPEG Audio Layer III, is a method of compressing audio files. MPEG is an acronym for Moving Picture Experts Group, which develops video data compression systems, including those used in DVD movies, television broadcasts, and digital satellite systems.

Using the MP3 compression system reduces the number of MP3 bytes in a song, while preserving CD-like quality sound. Every time you compress a song, its quality is degraded in order to carry more music files on a smaller storage system. A smaller file size also allows songs to download from the Internet faster.

Consider that the average song is about four minutes long. On a CD, that song uses about 40 megabytes (MB), but it uses only 4 MB if compressed into MP3 format. On average, 64 MB of storage is equivalent to an hour of music. A music listener who has an MP3 player with 1 GB (about 1000 MB) of storage space can carry about 240 songs or the equivalent of about 20 CDs. Songs stored on traditional CDs are already uncompressed, so more discs are needed to store the same number of songs. (Some CDs support MP3 files.)