The audio signal is an important part of the multimedia information. The audio signal can be divided into telephone quality language, AM broadcast quality audio signal and high fidelity stereo signal (such as FM broadcast signal, laser disc sound signal, etc.)
The digital audio compression technology standards are divided into three categories: telephone voice compression, AM broadcast voice compression, and FM audio and cd-quality broadband audio compression.
In the field of voice coding technology, various manufacturers are vigorously developing and promoting their own coding technology, which makes the coding technology in the field of voice coding a wide variety of products and poor compatibility. The technology of various manufacturers is also difficult to promote as soon as possible. Therefore, it is necessary to integrate the existing coding technology and formulate a globally unified language coding standard. Since the 1970s, ccett's fifteenth research group and the International Organization for Standardization (ISO) have successively introduced a series of speech coding technology standards. Among them, ccitt introduced the g-series standard, while ISO introduced the h-series standard.
1. Telephone (200Hz-3.4KHz) voice compression standard
There are mainly proposals for itu-based g.722 (64 kb/s), g721 (32 kb/s), g.728 (16 kb/s), and g.729 (8 kb/s) for digital telephone communications.
2. AM broadcast (50Hz-7KHz) voice compression standard
It mainly uses itu's g.722 (64kb/s) recommendation for high quality voice, music, audio conferencing and video conferencing.
3. Wideband audio compression standards for FM broadcast (20hz-15khz) and cd sound quality (20hz-20khz)
Mainly used mpeg-1 or mpeg-2 dual Dolby ac-3 and other recommendations for cd, md, mpc, vcd, dvd, hdtv and movie dubbing.
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