DVD MythsFar too many people present themselves as DVD experts without knowing the first thing about DVD. This is my response to the myths generated by helpful but clueless people. Suggestions are welcome.
These myths are debunked by facts. Dispute them at your peril. Read the DVD FAQ for more info.
[Last updated July 21, 2001.]
- Not HDTV compatible.
Current DVD players are compatible with HDTVs in the same way VCRs, camcorders, and laserdisc players are compatible. In order to take take advantage of the digital nature and progressive scan of HDTV, new DVD players will be required. These players will make current discs look even better on HDTVs, but won't provide full HDTV resolution. Eventually a new "HD-DVD" format will appear, based on blue lasers. The new format will require new discs and new players, but the players will play old DVD discs and CDs.
- DVD is unfinished, with competing formats.
The DVD-ROM and DVD-Video standards are finalized as single formats. There were once two competing formats (SD and MMCD) but they were combined to form DVD back in 1995. DVD-Audio is also finalized. There is no reason to delay buying DVD players or discs because of rumors that it might change. On the other hand, there are a number of competing, incompatible DVD recording formats (DVD-R/RW, DVD+R/RW, and DVD-RAM). It will take a while before the recordable DVD mess gets sorted out.
- Dolby Digital is 5.1 channels.
Dolby Digital (formerly called AC-3) carries from 1 to 5 channels of compressed digital audio, with an optional ".1" low-frequency effects (LFE) channel. The Dolby Digital track does not have to include 5.1 channels. It may be mono or stereo, and the stereo may or may not be Dolby Surround encoded (for playback on a system with a Dolby Pro Logic decoder).
- Audio is only 12 bits.
This myth was started by an article in Widescreen Review magazine that attempted to equate jitter in DVD players to a reduced audio resolution. DVD audio can be either 16, 20, or 24 bits. Jitter does not reduce the number of bits. There are many kinds of jitter. Jitter in the channel signal is accounted for in the readout circuitry. Jitter in the digital audio output is related to the audio circuitry and is independent of the DVD format. It's true that jitter at different stages can reduce audio quality, but comparing it to a 12-bit sample size is naive and inaccurate. Numerous reviews indicate that most DVD players sound as good or better than most CD transports.
- Audio level too low.
In truth the audio level is too high on everything else. Movie soundtracks are extremely dynamic, ranging from near silence to intense explosions. In order to support an increased dynamic range and hit peaks (near the 2V RMS limit) without distortion, the average sound level must be lower. This is why the line volume from DVD players is lower than from almost all other sources.
- 133 minutes per side.
This is a meaninglessly exact figure. A single-layer disc can easily hold 150 minutes at the typical average video data rate if there's only one audio track. Lowering the data rate slightly can accommodate over three hours on a single layer. Dual-layer discs can hold over four hours on one side.
- Playing CDs is harmful.
Playing an audio CD in a DVD player will not hurt the disc or the player. Some players use a single laser for reading DVDs and CDs, while others have separate lasers, but in either case there is nothing about the lasers that can damage a CD, nor is there anything about a CD that can affect the player.
- Digital artifacts.
Many reports of "artifacts" on DVD turn out on examination to have nothing to do with MPEG compression. Artifacts come from many sources: film problems, bad video transfer, improper TV settings, bad video connections, electrical interference, player faults, disc read errors, etc. Some of these can be corrected by adjusting the TV or cleaning the disc. Most DVDs exhibit few visible compression artifacts on a properly configured system. If you think otherwise, you are probably misinterpreting what you see.
- Players can't read dual-layer discs.
All DVD-Video players and all DVD-ROM drives are required to play dual-layer discs. A few faulty units might have problems reading dual-layer discs. Dual-sided discs must be flipped over by hand. (Only a few multi-disc changers can flip discs automatically.)
- DVD is a worldwide standard.
In addition to regional codes that can be used to prevent playback in different areas, DVD uses different formats for NTSC or PAL playback. Almost no US players can play PAL DVDs. All PAL players can play both PAL and NTSC DVDs, but only on a 60-Hz-capable PAL TV or a multistandard TV. Most DVD-equipped computers can play both NTSC and PAL discs.
Jim (the Frog) Taylor
Author of DVD Demystified and the DVD FAQ