Stay in touch…

Blog

Read the latest Bitstream

RSS Feed

LinkedIn

Look for us at LinkedIn

Twitter

Follow us on Twitter

Editorial

This article was originally published in November 1997 on TheMessage.com, the parent of Seneschal.net...

Opinions About DVD-V

Heard some buzz about DVD? Why should you care? Maybe you shouldn’t but, if you relish superior home reproduction of music and films, then you may be interested in this new consumer format. I won’t pretend to be impartial. I’ve been working with digital optical disc-based sound and motion pictures since 1986 when DVD progenitor, CD-i (née CD-I), was still considered a viable consumer format. I worked with a small group of great folks to create one of the first generation of all singing, all dancing, content creation tools for disc-based titles. We’re talkin’ bear skins and stone knives. The concept needed a bit of time for cost effective technology to catch up in the form of the current DVD standard. The promise of high quality audio, still and moving pictures as well as vast oceans of computer data inexpensively delivered to homes, schools and worksites has finally come to pass.

Still skeptical about the viability of the format? Think back to the early days of CD-ROM, when it took a rocket scientist to “integrate” a ROM drive into a desktop computer or workstation. When only technical documentation, specialized (read expensive) databases and bulky data sets appeared on CD-ROM. Then along comes Apple Computer and proceeds to ship Macs with no-brainer ROM drives. Poof...CD-ROMs suddenly become “accepted” and Microsoft jumps in with their ROM-XA standard to take advantage of “multimedia.”

Well, it’s happening again. You can already purchase Windoze upgrade kits at the local stores around here. DVD drives will appear in industrial Mac by year end. Consumers will have Mac upgrade kits real soon now and factory installed drives next year.

Anyway, DVD combines most of the compelling features of each CD format that has gone before, including CD-DA (plain ol’ audio CDs), CD-ROM, CD-i and CD-V. Lets look at some numbers...

DVD-3
DVD-5
DVD-9
DVD-10
DVD-18
Storage Capacity
2.6 GB
4.7 GB
8.5 GB
9.4 GB
17 GB
Physical Format
single
layer, 80 mm (3")
single
layer, 120 mm (5")
dual layer, 120 mm
dual side, 120 mm
dual layer
& side, 120 mm
Video Capacity (see below)
73 min.
133 min.
240 min.
133/side
240/side

 

Video capacity is an interesting figure since DVD supports “variable bit rate” or variable data compression of the encoded video or audio. If the author needs more data to convey audible or visual subtleties, then the bit rate can be cranked up. Assume an average rate of 4.69 Mbits/sec. for video, 3 audio channels and 3 subtitle channels; the transfer rate can increase up to 10 Mbits/sec when needed. Of course, storage capacity is reduced as data throughput is increased.

Getting more data into the same form factor is achieved in several ways. The track pitch, at 0.74 micrometers, is slightly less than half the current Yellow Book spec of 1.6 micrometers. A new, high efficiency channel coding method further improves data packing and a new error correction scheme compensates for the higher density to ensure the recovery of data without concealment or interpolation. This is a true multimedia disc, so it has to act like a CD-DA and CD-ROM. Muting or error concealment just doesn’t cut it for DVD-ROM.

Another method of increasing capacity is by going with two layers per side, one fully and the other partially reflective. Continuous play is seamless by reading outward on one layer, then inwards on the other. Bonding two back-to-back discs, a technique pioneered in ye olde analogue laserdisc days, doubles the capacity again. An added advantage of double sided discs is simpler backwards compatibility of the optical pickup with “old” CDs due to almost equal physical disc thickness. Tighter tolerances on optics, smaller pit/land structures and a shorter wavelength laser, 650 nanometers versus 780 for the CDs, all contribute to a larger bit bucket.

Other interesting features are support for Dolby Digital and MPEG audio. Dolby Digital, originally AC-3, handles 5 channels of full bandwidth, compressed linear pulse code modulation (LPCM) audio with a 20 to 120 Hz low frequency effect channel thrown in just for fun. MPEG audio goes one better with 7 channels, tucking a left-center and right-center speaker on either side of the center channel. This improves imaging as sources are panned across the front. Sounds like a consumer high-fi manufacturer’s dream come true, doesn’t it? Well, looks like the manufacturers in Europe haven’t got the DVD religion and even PAL titles will have Dolby Digital for multichannel audio.

Speaking of which, the spec also includes stereo LPCM sampling rates of 48 kHz and 96 kHz with a 16, 20 or 24 bit word length. The three word lengths translate into 96, 120 or 144 dB of dynamic range. Even if you don’t subscribe to the notion that frequencies past 20 kHz affect our aural perception, then at least you can go with the idea that an anti-alias filter can be better behaved with double the passband in which current filters have to work. Notice that there’s no support for 44.1 in the current standard. Time will tell us what the DVD-A standard will support but you may want to start recording those masters at 48, 88.2 or 96 kHz, if you haven’t already

.