eared in the mid 1990s, is still by far the most popular. The name is short for MPEG-1/2 audio layer 3. The encoded MP3 files (having the filename extension .mp3) are made of a sequence of independent of MP3 frames, as illustrated in Fig. G2. A given sequence may be "encapsulated" by heading metadata file (whose format is referred to as ID3 or APEv2). This tag contains information, such as the music title, author, artist, and track number. Each frame has an MP3 header field and an MP3 data field. The four- byte header contains a sync-marker word (12 bits), the number of the MPEG and layer versions (3 bits), the bit rate (4 bits, e.g., 1010 = 160 bit/s, for instance), the sampling frequency (2 bits, e.g., 00 = 44.1 kHz), and other size information. There are lots of available bit rates in the two MPEG-1/2 standards, with B = 128 kbit/s or B = 192 bit/s being most often chosen as de facto values. The bit rate can also be varied from http://en.wikipedia.org/wiki/Psychoacoustic_model www.sfu.ca/sonic-studio/handbook/Psychoacoustics html; www.binaural.com/serendipity/index.php?/archives/62-Tutorial-The-Psychoacoustics-of Multichannel-Audio.html 19 See, for instance: http://en.wikipedia.org/wiki/MP3, www.mp3-tech.org/; www.mpeg.org/MPEG/mp3. html#overview; www.pcmag.com/encyclopedia_term/0,,t=mp3&i=47286,00.asp. Appendix G one MP3 frame to the next, which allows one to allocate more bits to the most dynamic music segments (i.e., with more complex spectral movements) and fewer bits in the less dynamic ones. Thus, a rate of 224 kbit/s would be used for a symphonic orchestra, while 48 kbit/s is sufficient for music made of pure frequency tones. These figures are to be compared with the bit rate of uncompressed CD-quality recording, which, as we have seen is 1.411 Mbit/s, which explains the aforementioned 10x to 12x average compression improvement. As for the MP3 data field, the size depends on the number of time-frequency samples or the sampling rate. For the S = 44.1 kHz sampling-rate case, there are exactly 1152 one-byt