Senior Consulting Engineer
Research and Advanced Development,
Cambridge Research Lab
"Can you dig it ... New York State Throughway's closed, Man. Far
out, Man," announced a young Arlo Guthrie in the vernacular on
the stage at Woodstock in 1969. Reading these words may evoke a
mental picture of the event, but it sure is a lot more fun to
hear and see Arlo deliver this message. Audio and video
technology is the featured theme of this issue of the
Digital Technical Journal.
Four years before Arlo's traffic report, in the year
that a young Digital Equipment Corporation introduced the PDP-8,
an interesting forecast was made. Gordon Moore, who was yet to
co-found Intel, asserted in a little-noticed paper that the power
and complexity of the silicon chip would double every year (later
revised to every 18 months). This prediction has been generally
accurate for 30 years and is today one of the most celebrated and
remarkable "laws" of the computer industry.
While we enjoyed this exponential hardware ride, there was always
some question about the ability of applications and software to
keep up. If anything, the opposite is true. Software has been
described as a gas that immediately fills the expanding envelope
of hardware. Ever since the hardware envelope became large enough
to begin to accommodate crude forms of audio and video, the
pressure of the software gas has been great indeed. Digitized
audio and video represent enormous amounts of data and stress the
capacities of real-time processing and transmission systems.
Digital has participated in expanding the envelope and in filling
it; its hardware performance is record-breaking and its audio and
video technologies are state-of-the-art. Looking specifically at
the four categories into which computer companies segment audio
and video technologies, Digital is making contributions in each
of these: analysis, synthesis, compression, and input/output.
MIT's Nicholas Negroponte believes that practical analysis, or
interpretation, of digitized audio and video will be the next big
advance in the computer industry, where nothing has changed in
human input (keyboard and pointing device) since, well, the
Woodstock era. Digital is actively investigating methods for
speaker-independent speech recognition and, in the area of video
analysis, means to automatically detect, track, and recognize
The synthesis of still and motion video, more commonly referred
to as computer graphics, has traditionally been a much larger
area of focus than the handling of sampled video. Synthesis of
audio, or text-to-speech conversion, is the topic of one of the
papers in this issue; DECtalk is largely considered to be the
best such synthesis mechanism available.
When audio or video data are represented symbolically, as is the
case after analysis, or prior to synthesis, a most efficient form
of compression is implicitly employed. However, the task of
storing or transmitting the raw digitized signal can be
overwhelming, especially at high sampling rates. Compression
techniques are relied upon to ease the volume of this data in two
ways: (1) reducing statistical redundancy, and (2) pruning data
that will not be noticed by exploiting what is known about human
perceptual systems. In this climate of interoperability and open
systems, Digital recognizes the importance of adhering to
accepted standards for audio and video compression versus the
promotion of some proprietary representation.
The last category is that of I/O. Audio and video input require a
means for signal acquisition and analog-to-digital conversion.
The focus here is on preserving the integrity of the signal as
opposed to interpreting the data. Proper rendering is needed for
good-quality output, along with digital-to-analog conversion. For
both audio and video, trade-offs must be made to accommodate the
highest degree of sampling resolution in time and amplitude.
Digital is a leader in the area of video rendering with our
AccuVideo technology, aspects of which are described in part in
three papers in this issue. Video rendering incorporates all
processing that is required to tailor video to a particular
target display. This includes scaling and filtering, color
adjustment, dithering, and color-space conversion from video's
luminance-chrominance representation to RGB. In its most general
form, Digital's rendering technology will optimize display
quality given any number of available colors.
The earliest form of AccuVideo appeared in a 1989 testbed, known
internally as Pictor. This led to the widely distributed research
prototype called Jvideo in 1991. Jvideo was a TURBOchannel bus
option with JPEG compression and decompression and was the first
prototype to combine dithering with color-space conversion.
Jvideo was the basis for design of the Sound & Motion J300
product, which included a remarkably improved dither method. A
follow-on to J300 is a PCI-bus version called FullVideo Supreme.
In products that render RGB data instead of video, Digital's
rendering technology is referred to as AccuLook; except for this
one difference, the rest of the rendering pipeline is identical
to AccuVideo. AccuLook products include graphics options for
workstations: ZLX-E (SFB+) designed for the TURBOchannel and
ZLXp-E (TGA) designed as an entry-level product for the PCI bus.
AccuVideo rendering is a key feature in the DECchip 21130 PC
graphics chip and in the TGA2 high-end workstation graphics chip.
While noted for its high image quality, AccuVideo is also
efficiently implemented in software; it is available as part of a
tool kit with every Digital UNIX, OpenVMS, and Windows NT
With Moore's law on the loose, it can be argued that hardware
implementations of video rendering are not justified as
software-only versions grow in speed. Although today's processors
can indeed handle the playback of video by both decompressing and
rendering at a quarter of full size, little is left for doing
anything else. Moreover, users will want to scale up the display
sizes, and perhaps add multiple video streams -- and still be
able to use their processors to do other things. For the near
term, hardware video rendering is justified.
The five papers that make up the audio and video technology theme
of this issue are but a small sampling of the work under way in
this area at Digital; look for more papers to follow in
subsequent issues of this Journal. As the audio and video gas
continues to fill the ever-expanding hardware envelope, we look
forward to an enriched and more natural experience with computing
devices. Arlo's Woodstock pals would likely agree that this
sounds like more fun.