Hardware AutopsyHarHardwardware Autopsye Autopsy
is that two things affect your perception of
sounds around you: the difference in ampli-
tude of the sound in each ear, and the delay
between hearing the sound in one ear, and
hearing the sound in your other ear.SURROUND-SOUND VIA
HEADPHONES
If you’re given pairs of HRTFs for the fi ve
loudspeaker directions specifi ed for typical
surround-sound systems, it should be
straightforward to transform each of the
main audio signals from a 5.1-channel DVD
audio program for headphone playback: You
would just apply the appropriate left-ear and
right-ear fi lters to each signal, producing
fi ve two-channel signals that can then be
simply mixed together. How the fi ltering is
done is a technical detail that boils down to
a DSP (digital signal processor) problem that
engineers can solve effi ciently.
In a perfect world, the result should be
identical to what you would hear if you were
listening to playback via those fi ve loud-
speakers out in the middle of a fl at snowfi eld
(rather than in a room which will add its own
reverberation to the sounds reaching your
ears). Because this is not a perfect world,
at least with regard to sound reproduction,
there will always be noticeable differences.
Besides room reverberation, one of the
most obvious differences is that turning your
head during headphone listening produces
a strange result: The virtual sound sources
move as your head turns, so the sound
maintains a constant direction relative to
your head, rather than remaining at stable
positions within the listening environment. In
contrast to loudspeaker listening, in which
you can turn your head to bring your nose
into alignment with the right-front loud-
speaker, headphone presentation of virtual
sources arriving from the angle of the right
speaker will shift 30 degrees to the right with
that same head turn.
This might not seem to be a problem for
casual listening, but the result can be very
disappointing while watching movies or play-
ing games, where you want to be able to dis-
tinguish between sources intended to arrive
from frontward versus rearward directions.
The solution is to incorporate head-tracking
technology into the surround-sound head-
phones you’re designing.HEAD TRACKING EXPLAINED
Head tracking is the means whereby chang-
es in the angle of your head (and sometimes
even its position) are actively sensed by a
peripheral device, which might be connectedr&dBREAKING DOWN TECH —PRESENT AND FUTURE
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White Paper: 6irtUAL $ AUdiO
BACKING An LCD’s backing sits squarely atop a cluster of
PCBs assigned with various functions. Small holes around the
perimeter of the backpiece promote airflow to these electronic
parts; larger holes, shown here at the indented midsection, pro-
vide openings for the ports (DVI, VGA, power, etc.) that make it
possible for your PC to interface with the device.
CONTROL BOARD This green PCB
receives a signal from the videocard,
by way of the VGA connector (in this
example) located at the lower-left cor-
ner. Here the signal is processed into
something the LCD can display.BACKLIGHT
CONTROLLER
When you make
adjustments to a
screen’s bright-
ness via the
onscreen display,
the information is
sent to the back-
light controller
by way of the
control board.LCD MODULE This metal hous-
ing contains the backlight and the
LCD glass. The signal from the
control board is fed to a PCB that
spans the top edge of the LCD
module (not visible here) and which
contains the LCD controller, driver,
and temperature compensation
circuitry.FRONT-PANEL CONNECTOR This narrow PCB directly
connects to the buttons along the bottom-front of the moni-
tor—those used to control brightness, contrast, color adjust-
ments, etc.—and sends a signal, based on a user’s input, to
the control board.LCD Monitor
Don’t let its slim figure fool you; a typical LCD desktop display is home to a lot more
than just a skinny screenPOWER SUPPLY
An alternative to
a power brick, a
built-in power sup-
ply converts AC
power from the
wall socket into DC
power the monitor
can use.Continued on next pageË