Mp3 (an audio encoding method) Part 3

To generate bit-compliant (Layer 1.Layer 2.Layer 3) MPEGAudio files, ISO MPEG Audio committee members developed reference simulation software in C called ISO 11172-5.

It can demonstrate the first real-time DSP-based hardware decoding of compressed audio on some non-real-time operating systems. Various other MPEG audio was developed in real time for digital broadcasting (DAB radio and DVB TV) for consumer receivers and set-top boxes.
Later on July 7, 1994, Fraunhofer-Gesellschaft released the first MP3 encoder called l3enc.
The Fraunhofer development team selected the .mp3 extension on July 14, 1995 (previously the extension was .bit). Using Winplay3 (released September 9, 1995), the first real-time software MP3 player, many people were able to encode and play MP3 files on their own personal computers. Since hard drives at the time were relatively small (such as 500MB), this technology was essential for storing entertainment music on computers.
MP2, MP3 and Internet
In October 1993, MP2 (MPEG-1 Audio Layer 2) files appeared on the Internet and were often played by Xing MPEG Audio Player and later MAPlay developed by Tobias Bading for Unix. MAPplay was first released on February 22, 1994 and ported to the Microsoft Windows platform.
The only MP2 encoder products at first were Xing Encoder and CDDA2WAV, a CD ripper that converts audio tracks from CDs to WAV format.
Often considered the father of the online music revolution, the Internet Underground Music Archive (IUMA) was the first hi-fi music site on the Internet, with thousands of licensed MP2 recordings before MP3 and the web became popular. .
From the first half of 1995 to the end of the 1990s, MP3 began to flourish on the Internet. MP3’s popularity is largely due to the success of companies and software packages such as Winamp released by Nullsoft in 1997 and Napster released by Napster in 1999, and they are mutually reinforcing. These programs make it easy for normal users to play, create, share and collect MP3 files.
The debate about sharing MP3 files between peers has spread rapidly in recent years, mainly because compression makes file sharing possible, uncompressed files are too large to share. Since MP3 files are widely spread over the Internet, Napster has been sued by some of the major record labels to protect their copyright (see Copyright).
Commercial online music distribution services, such as the iTunes Music Store, often choose other proprietary or DRM-enabled music file formats to control and limit the use of digital music. Formats that support DRM are used to protect copyrighted material from copyright infringement, but most protection mechanisms can be broken in some way. Computer experts can use these methods to generate unlocked files that can be freely copied. One notable exception is Microsoft’s Windows Media Audio 10 format, which has yet to be cracked. If a compressed audio file is desired, the recorded audio stream must be compressed and the sound quality will be degraded.
streaming audio quality
Because MP3 is a lossy compression format, it offers a variety of options for different “bit rates,” that is, the number of encoded data bits needed to represent the audio per second. Typical speeds are between 128 kbps and 320 kbps (kbit/s). In contrast, the uncompressed audio bitrate on a CD is 1411.2 kbps (16 bits/sample × 44100 samples/sec × 2 channels).
MP3 files encoded with lower bit rates generally play at a lower quality. If you use too low a bitrate, “compression artifact” (sounds not present in the original recording) will appear during playback. A good example of compression noise is the sound of compressed cheering; due to its randomness and sharp changes, encoder errors are more pronounced and sound like echoes.

Mp3 (an audio encoding method) Part 2

MPEG-1 Audio Layer 2 encoding began as a digital audio broadcast (DAB) managed by Egon Meier-Engelen at the German Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (later known as Deutsches Zentrum für Luft- und Raumfahrt, German Space Center). )draft.

This project is funded by the European Union as a EUREKA research project, and its name is commonly known as EU-147. The study period for EU-147 was from 1987 to 1994.
2. By 1991, two proposals had emerged: Musicam (called Layer 2) and ASPEC (Adaptive Spectrum Sensing Entropy Coding). The Musicam method proposed by Philips of the Netherlands, CCETT of France, and the Institut für Rundfunktechnik of Germany was chosen due to its simplicity, error robustness, and lower computational effort in high-quality compression. The Musicam format based on subband coding is a key factor in determining the MPEG audio compression format (sample rate, frame structure, header, sample points per frame). This technology and its design philosophy are fully integrated into the definition of ISO MPEG Audio Layer I, II and later Layer III (MP3) formats. The standard was developed by Leon van de Kerkhof (Layer I) and Gerhard Stoll (Layer II) under the auspices of Prof. Mussmann (University of Hannover).
3. A working group consisting of Leon Van de Kerkhof from the Netherlands, Gerhard Stoll from Germany, Yves-François Dehery from France and Karlheinz Brandenburg from Germany absorbed design ideas from Musicam and ASPEC and added their own design ideas to develop an MP3. MP3 can achieve MP2 sound quality from 192 kbit/s to 128 kbit/s.
4. All of these algorithms eventually became part of the first group of MPEG standards, MPEG-1, in 1992, resulting in the international standard ISO/IEC 11172-3 published in 1993. Further work on MPEG audio was eventually became part of the MPEG-2 standard, a second group of MPEG standards developed in 1994, officially known as ISO/IEC 13818-3, first published in 1995.
5. The compression efficiency of the encoder is generally defined by the bit rate, because the compression rate depends on the number of bits (: in: bit depth) and the sampling rate of the input signal. However, there are often products that use CD parameters (44.1 kHz, two channels, 16 bits per channel, or 2×16 bits) as the compression ratio reference, and the compression ratio using this reference is usually higher, which which also shows that the compression ratio is very important for lossy compression problems.
6. Karlheinz Brandenburg used Suzanne Vega’s song Tom’s Diner on CD to test MP3 compression algorithms. This song is used because the song’s smooth and simple melody makes it easier to hear glitches in the compressed format during playback. Some jokingly refer to Suzanne Vega as “the mother of MP3”. Some more serious and critical audio extracts (glockenspiel, triangle, accordion…) from the EBU V3/SQAM reference CD are used by professional audio engineers to assess the subjective perceived quality of the MPEG audio format.

Mp3 (an audio encoding method)

MP3 is an audio compression technology, its full name is Moving Picture Experts Group Audio Layer III, called MP3.

It is designed to drastically reduce the amount of audio data. Using MPEG Audio Layer 3 technology, music is compressed into a smaller capacity file with a compression ratio of 1:10 or even 1:12, and for most users, playback quality is not as good as the original uncompressed. audio Significant decrease. It was invented and standardized in 1991 by a group of engineers at the Fraunhofer-Gesellschaft research organization in Erlangen, Germany. Music stored in the form of MP3 is called MP3 music, and a machine that can play MP3 music is called an MP3 player.

Motion Picture Expert Compression Standard Audio Layer 3 foreign name Moving Picture Expert Group Audio Layer III research organization Fraunhofer-Gesellschaft type audio coding advantage Drastically reduce the amount of audio data defect sound quality loss
content
1 Features
2 story
▪ origin
▪ go to the masses
3 audio quality
4 patent issues
transmission characteristics
MP3 converts the time-domain waveform signal to a frequency-domain signal by taking advantage of the human ear’s insensitivity to high-frequency sound signals and splits it into multiple frequency bands, using different compression rates. for different frequency bands and increasing the compression ratio for high frequencies (even ignoring the signal) Use a small compression ratio for low frequency signals to ensure that the signal is not distorted. In this way, it is equivalent to discarding the high-frequency sound that is basically inaudible to the human ear [1], keeping only the audible low-frequency part, thus compressing the sound with a compression ratio of 1:10 or even 1: 12. Because the full name of this compression method is called MPEG Audio Player3, people call it MP3 for short.
According to the MPEG specification, AAC (Advanced Audio Coding) in MPEG-4 will be the next generation of the MP3 format.
Compared to CD, FLAC and APE lossless compression formats, the sound quality of the highest parameter MP3 (320 Kbps) is not much different.
MP3 players are dying
When they first came out, MP3 players were at the forefront of the digital revolution. However, sales of iPods and other MP3 players in the UK fell sharply in 2012 as consumers turned to other digital products such as smartphones.
In 2012, sales of MP3 players in the UK market were £110m ($178m), just 29% of the £381m in 2011, according to market research firm Mintel. Mintel expects total MP3 player sales in the UK market to halve by 2017. In the worst case scenario, total MP3 player sales in the UK market will be just 25 million dollars five years later. [23]
1. MP3 is a data compression format;
2. Discards pulse code modulation (PCM) audio data that is not important to the human ear (similar to JPEG is a lossy image compression), resulting in a much smaller file size;
3. MP3 audio can be compressed according to different bit rates, providing a variety of trade-offs between data size and sound quality. The MP3 format uses a mixed conversion mechanism to convert audio domain signals. time in frequency domain signals;
4. 32 band polyphase integral filter (PQF);
Modified discrete cosine filter (MDCT) of 5, 36 or 12 taps; each subband size can be independently selected between 0…1 and 2…31;
6. MP3 not only has extensive client software support, but also has a lot of hardware support, such as portable media players (referring to MP3 players), DVD and CD players, outgoing calls