Media Types

CD was developed primarily as a recording media but later adopted for other forms of data storage. Audio CD has been available since 1982. Although now at the end of its reign, the CD format is still generally considered to be the main source in a system.

The disc itself is some 120 mm in diameter; it can hold 700 Mb of data or 80 mins of audio as a direct replacement for the LP. Data is recorded as a continuous spiral beginning at the inside of the disc. A CD can store up to 99 tracks. Data is stored as a series of indentations which is read by a laser. Data is read by the laser interpreting the edges of the dots. The linear velocity of the scanning is 1.2 – 1.4 m/s relating to the disc spinning at 200 – 500 rpm. This relates to a continuous track of 5.38 km. The beginning or the end of a dot is interpreted as a 1 the flat areas are read as 0’s. It was invented by Sony and Philips as a spin off from Laserdisc. In 1990 CD-Recordable was introduced. Since the introduction of MP3 sales have diminished. CD uses 44.1 kHz sampling with 16 bit depth. This was designed to accommodate a frequency response of  20 Hz – 20 kHz ± 0.5 dB, and a dynamic range of 96 dB.

The main shortcoming of CD is that it is now dated, and is considered to be short of disc data. It’s still the medium preferred by the mass market. I’ll bet there are not many music collections out there that are not dominated by CD’s. Whilst other formats offer better sampling rates, the majority of music is only available on CD. However in spite of it’s shortcomings a well recorded CD on a decent system is capable of giving superb results.