MPEG-1 Audio Layer

Early computer software used to play music yms limited to WAV (binary waveform audio file format) and textual MIDI (musical instrument digital interface) files and, while interesting, was not widely used. Better file formats, in particular, MP3 (MPEG-1 audio layer 3) files, have produced high-quality reproductions that are small enough to download and store easily, and this has greatly increased audio player software. Early video software also was limited by file... 

Adaptive filter banks. In the basic configuration, all filter banks described above feature a time/frequency decomposition which is constant over time. As mentioned above, there are possibilities to switch the characteristics of a filter bank, going from one time/frequency decomposition to another one. We explain the basic principle using the example of MPEG Audio Layer 3 ... 

The frequency domain representation of the data is calculated via an FFT after applying a Hann window with a window length of 1024 samples. The calculation is done with a shift length equal to the block structure of the coding system. As described below, the shift length is 576 samples for Layer 3 of the ISO/MPEG-Audio system. 

Non-uniform scalar quantization. While usually non-uniform scalar quantization is applied to reduce the mean squared quantization errors like in the well known MAX quantizer, another possibility is to implement some default noise shaping via the quantizer step size. This is explained using the example of the quantization formula for MPEG Layer 3 or MPEG-2 Advanced Audio Coding ... 

While file formats are recognizable by the file extension (such as. wav,. txt or. html), audio and video file formats may also be wrappers around the real format (or codec) of a file. For example, a. wav file might use the PCM (uncompressed) format or the MPEG Layer-3 format. See the section on codecs for more information. 

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