106 Personal Content Experience: Managing Digital Life in the Mobile Age Figure 4-7. The layout of an MP3 fi le with ID3 tags. 4.6.5 Acidized Wav Contemporary music production is based on loops, particularly for the great majority of songs in the western Top50 charts. Pop songs typically consist of individual audio samples that are repeated and recombined using a variety of methods, including sample playback and sample re- synthesis. Traditionally this was done in expensive commercial music studios, but in the last decade hundreds of more affordable software tools have appeared that allow hobbyists, semi-pros, and amateur musicians to craft technically advanced pieces of music in their bed- rooms. Most professional musicians now have smaller so-called “project studios” for creating music on their own. This has resulted in an esti- mated 350 37 000 project studios worldwide. Many of these studios use existing sound samples as their source material. Such samples are avail- able from a variety of sources, including sample collections on CDs and downloads from the Internet. The ACID fi le format for audio sample fi les quickly became popular with both professionals and amateur musicians when it was established in the late 1990s. Designed by Sonic Foundry for their ACID audio manipulation software, the format embeds extra information about the 37 Source: Anthony Grimani, Performance Media Industries (PMI) Ltd, Fairfax, CA, USA, in AES 121 conference in San Francisco, October 2006 (http://www.aes. org/121)