th a unique, 24- or 27-bit synchronization codeword, acting as a frame delimiter. The whole frame conversion results in 33 X (14 + 3) + 27 = 588 bits. Like any computer disk, the CD is organized into sectors, each sector containing 98 frames. The aforementioned one-byte subcode, thus, provides eight channels with 98 bit/sector to ensure various functions, like track monitoring and timing or indexing information within tracks. The standard reading speed being set to 75 sectors per second, we obtain the channel rate: 588 bit/frame X 98 frame/sector X 75 sector/second = 4.32180 Mbit/s. After EFM demodulation and decoding, overhead removal, and error correction, the user (or payload) channel rate is reduced to 2 X 16 bit X 44.1 kHz = 1.4112 Mbit/s. The physically recorded program area is 86.05 cm², with a track pitch of p = 1.5- 1.6 um. Thus, the full length of the track (referred to as the "recordable spiral") is l = 86.05 cm2 X 10-4 cm = 5.73-5.38 km. With a standard scanning velocity of V = 1.2 m/s, the corresponding playing time is t = l/v = 75-80 minutes. At the user rate, this corresponds to 1.470 (Mbit/s) X t(s) = 6615-7056 Mbit or 826-882 Mbyte, which, after some extra sector or error-correction overhead (representing 13%), 10 yielding 720- 767 Mbytes, is quite close to the storage capacity offered by current CD-ROM vendors (750-800 Mbytes). The CD-ROM standard will be described later under the heading "Files." Why this 75-80 minute duration for audio CDs? One alleged explanation is that CDs had to be able to play the entire Beethoven's 9th symphony, which took exactly 74 minutes in the slowest recording at the time. 11 Any program that performs digital encoding and decoding is referred to as a codec (short for coder-decoder, compressor-decompressor, or compression-decompression algorithm). Thus, audio codecs represent the family of codes and algorithms that generate digital audio files and restore the sound to the human ear. As we have seen earlier, the audio codec used in CDs is based on PCM with 44.1 kHz s