EFMPlus

EFMPlus. It is a channel code developed by Kees A. Schouhamer Immink and adopted as the standard modulation scheme for the DVD optical disc format, succeeding the earlier Eight-to-Fourteen Modulation (EFM) used in Compact Disc (CD). The code translates 8-bit data words into 16-bit channel words, optimizing for higher storage density and robust error correction within the constraints of the physical optical disc medium. Its design was crucial for enabling the significantly larger capacity of DVDs compared to CDs.

Overview

EFMPlus was created to address the limitations of the original Eight-to-Fourteen Modulation used in the Compact Disc system. The primary goal was to increase data density for the next-generation DVD format, a joint project spearheaded by the DVD Forum consortium involving companies like Philips, Sony, Toshiba, and Panasonic. The code's development was driven by the need for efficient DC control to maintain reliable readback from the disc, a critical factor in optical storage technology. Its adoption represented a major advancement in data storage, allowing full-length movies to be stored on a single disc.

Technical details

The encoding scheme converts 8-bit data bytes into 16-bit channel bits using a state-dependent finite-state machine with four possible states. This state machine architecture allows the encoder to choose between two possible channel words for each data word, a process used to control the low-frequency content, or digital sum value (DSV), of the resulting signal. The constraints include a minimum run length of 3 channel bits (d=2 constraint) and a maximum run length of 11 channel bits (k=10 constraint), which are essential for clock recovery and reducing inter-symbol interference. These parameters are carefully balanced to maximize the code rate while adhering to the physical limitations of the laser and photodiode systems in DVD players.

Comparison with EFM

While both EFM and EFMPlus serve the same fundamental purpose in optical disc systems, EFMPlus offers several key improvements. The original Eight-to-Fourteen Modulation used in the Compact Disc has a lower code rate (8/17 ≈ 0.47) compared to EFMPlus (8/16 = 0.5), directly contributing to a 6% increase in storage efficiency. Furthermore, EFM required three merging bits between each 14-bit channel word, whereas EFMPlus generates seamless 16-bit words, simplifying the encoding and decoding process. The enhanced DC control in EFMPlus also provides superior resilience against baseline wander and tracking errors compared to the method used in the Red Book (CD standard).

Applications and usage

The primary application of EFMPlus is in the DVD-Video and DVD-ROM formats, where it is the mandatory physical layer modulation code. It is also employed in the Super Audio CD (SACD) format, developed by Philips and Sony, for encoding high-resolution Direct Stream Digital audio data. The code's reliability and efficiency made it a cornerstone technology for the optical disc drive industry throughout the late 1990s and 2000s. While largely superseded by more advanced codes like the 17PP code used in Blu-ray Disc, EFMPlus remains in widespread use in the vast installed base of DVD players and drives worldwide.

Standardization and patents

EFMPlus was standardized by the DVD Forum and is detailed in the official DVD specification books, such as the DVD-ROM Book. The underlying patents for the technology are held primarily by Philips and Sony, who licensed it to disc and drive manufacturers. The licensing framework was managed through the DVD6C Licensing Agency, a patent pool that also covered other essential DVD technologies. The development and standardization process involved significant contributions from the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO), ensuring global interoperability for the format.

Category:Data transmission Category:Computer storage codes Category:DVD