ML-recording can increase capacity by a factor of 1.9. MultiLevel optical recording is an example of baseband pulse-amplitude modulation. While Non-binary, or M-ary, modulation is common in the telecom industry, the technique was originally developed and patented for optical disc recording at Optex Corporation in the early 1990s (in conjunction with the University of Rochester) for use with their Electron Trapping Optical Media (ETOM). Although simple in principle, implementation of ML was challenging, in large part because data storage channels are highly nonlinear. The overall ML-system response is much more sensitive to variations in its individual components (operating temperature, media uniformity, read-head fluctuation, etc.) than a conventional CD/DVD system. To compensate, the ML logical-format devotes a substantial portion of bits (as forward-error correction coding) to enhance robustness against media defects and signal noise. ML-drives used sophisticated power-optimization during writing and adaptive equalization during reading. MultiLevel recording is sometimes confused with multi-layer storage, in which multiple data surfaces are combined into a single disc. Multi-layer and multiLevel technique can be combined (as in dual-layer ML-DVD ROM), where ML-modulation is applied to each individual layer of the disc. References External links USPTO Link to Optex M-ary patent 120 mm discs Audio storage Video storage Optical computer storage