This thinner substrate diffuses and refracts less light from the laser pick-up, and results in greater reading accuracy by the laser. Besides improving tilt margins, bonded substrates strengthen the disc, prevent warping and make the disc more resilient to changes in temperature and humidity. The amount of variation in the laser focus, cased by the physical characteristics of a disc, that can be accommodated while maintaining signal integrity is referred to as the Tilt Margin. The 0.6mm substrate of a DVD diffuses less of the laser's focus than does a conventional CD's 1.2mm substrate, resulting in a more accurate beam spot. The bonded substrates of a DVD reduces warpage and further improves tilt margins.
Tracking is important for the most accurate reading of the information being retrieved from a disc.
The laser reads the primary information that represents the audio and video signals to be displayed, as well as pits on either side of the main track which serve to provide tracking information. The information they return to the pick-up keeps the main beam spot aimed at the correct track on the disc, resulting in accurate retrieval of digital information. The flow of data, or bit rate, of a DVD is variable depending on the complexity of the signal being processed. A detailed, rapidly moving scene with multiple picture elements would require a high bit rate, while a static image with little detail would receive far fewer bits. This advance in processing, a part of the MPEG-2 system, uses bits more efficiently, allocating storage capacity according to the requirement of the signal.