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Audio codecs are software algorithms that allow the users to compress and decompress audio. Sasken Inc offers a comprehensive portfolio of audio codec implementations that conform to the main standards in the industry.
 Advanced Audio Coding (ACC) |
AC3 (Dolby Digital) |
| MPEG-1 Audio Layer 3(MP3) |
Windows Media Audio(WMA) |
AAC (Advanced Audio Coding) is considered the successor to MP3 audio format. AAC demonstrates greater sound quality and transparency than MP3 files that are encoded at the same bit rates. AAC was initially developed by a consortium that consists of Fraunhofer IIS, AT&T Bell Laboratories, Dolby, Sony and Nokia. It was declared as an international standard by the Moving Pictures Experts Group (MPEG) in April 1997. Today AAC is part of both the MPEG-2 and MPEG-4 specifications. MPEG-2 audio tests have shown that AAC meets the requirements referred to as "transparent" for the ITU specification at 128kbps for stereo.
AC3, or Dolby Digital, is a codec developed by Dolby Laboratories in 1992. It supports up to 6 channels of audio encoding and decoding. It has many modes of operation. However, the most prominent mode is intended to be used with five channels for normal-range speakers (20Hz - 20,000Hz) and one channel for a subwoofer (20Hz - 120Hz) in lower frequencies. Sometimes 6 channels are downmixed into 2 channels to provide stereo sound for certain speaker configurations. The 6 channel mode is usually called 5.1 because of 5 surround channels (left front, center, right front, left rear, right rear) and 1 subwoofer channel.
MP3 (MPEG-1 Audio Layer 3) is the most common audio format that is available on the Internet today. MP3 was designed by MPEG and approved as an ISO/IEC standard in 1991. MP3 uses a lossy compression algorithm that is designed to reduce the amount of data required to represent the audio recording and still sound like a faithful reproduction of the original uncompressed audio for most listeners, but is not considered high fidelity audio by audiophiles. An MP3 file that is created using the mid-range bit rate setting of 128 kbit/s will result in a file that is typically about 1/10th the size of the CD file created from the original audio source. An MP3 file can also be constructed at higher or lower bit rates, with higher or lower resulting quality. The compression works by reducing accuracy of certain parts of sound that are deemed beyond the auditory resolution ability of most people. This method is commonly referred to as perceptual coding. It internally provides a representation of sound within a short term time/frequency analysis window, by using psychoacoustic models to discard or reduce precision of components less audible to human hearing, and recording the remaining information in an efficient manner. This is relatively similar to the principles used by JPEG, an image compression format.
Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. It is a proprietary technology that forms part of the Windows Media framework. The WMA platform consists of three common codecs:
A WMA file is in most circumstances encapsulated, or contained, in the Advanced Systems Format (ASF) container format, featuring a single audio track in one of following codecs: WMA, WMA Pro or WMA Lossless. These codecs are technically distinct and mutually incompatible. The ASF container format specifies how metadata about the file is to be encoded, similar to the ID3 tags used by MP3 files. Metadata may include song name, track number, artist name, and also audio normalization values.
This container can optionally support digital rights management (DRM) using a combination of elliptic curve cryptography key exchange, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function. Microsoft's DRM technology is called Windows Media DRM.