Write down the factors that determine the quality of digital audio. Describe the specification of CD-DA quality audio
|Subject||Computer Graphics and Multimedia|
|NU Year||Set: 4.(c) Marks: 2+2=4 Year: 2011|
Digital audio files are so large, reduced sample rates were typically used whenever possible. In 1991, the MP3 (MPEG I, layer 3) standard changed everything. MP3 is a lossy compression technique that can dramatically reduce the file size of a digital audio file with surprisingly little effect on the quality. One second of CD-quality audio takes up 1.4 megabits, while a common bit rate for MP3 files is 128 kbps, which is a compression factor of more than 10x! MP3 works by cleverly "throwing away" details about the audio waveform that humans are not very sensitive to, based on a psychoacoustic model of how our ears and brains process sounds. All MP3 files are not created alike; different psychoacoustic models will lead to different amounts of perceived distortion in the audio file.
CD-DA stands for Compact Disc-Digital Audio and was developed by Sony and Philips in the 1980s and is defined in the Red Book standard. It is exactly the same format as CDA, it is just that CDA is a more succinct abbreviation than CD-DA and so is more commonly used.