The next few chapters use the example of the CD audio system to show some of the basic properties of instruments used to gather and process information. CD has been selected for various reasons. It provides an excellent example of many digital data processing methods and allows us to explore the relationship between signals held in equivalent analog and digital forms. Both the source information gathering (i.e. the recording studio, etc.) and the information replay system (the CD player) can be used to illustrate a variety of highly effective measurement and information processing techniques. The CD system can also be simultaneously regarded as:

i) A measurement system, collecting audio information. ii) A signal processing system. iii) An information communication channel/storage system.