Specifications

JANUARY 2005 MAXIMUMPC 47
Like Doom 3, Half-Life 2 eschews hardware sound inter-
faces like EAX and DirectSound3D in favor of a homegrown,
CPU-based audio engine. Valve’s engineers found they sim-
ply couldn’t deliver the high-quality aural experience they
wanted using current technology. Its proprietary sound engine
employs some clever tricks, detailed below, to create sound
that behaves much like it does in the real world. The overall
effect is extremely convincing.
Many sound effects in Half-Life 2 are split in two—a high-
frequency portion and a low-frequency portion. By play-
ing different combinations of the high- and low-frequency
sounds, the engine can approximate the way sound functions
in the real world. For example, when you hear a sound under
water, the game fades out the high frequencies, but leaves in
the low frequencies.
Likewise, when an object comes between you and a sound
source, the high-frequency sounds are reflected by the object
and never make it to you. In real life, low-frequency sounds
are not as easily reflected. To emulate this effect, the Source
engine automatically drops out the high-frequency sound
effects in these situations. If you’re in close proximity to an
explosion or gunshot, the engine cranks up the high- and
low-frequency sounds for dramatic effect.
In addition to storing physics information for all the objects
used in the game, the materials engine also stores sound
effects for the various materials. Fire three shots into a piece
of wood, and you’ll hear three slightly different sounds. This
isn’t limited to bullet impacts, either. When two materials—say
the metal of a barrel and the earthen ground—collide, they
make one of many unique sounds.
Because they weren’t using standard sound APIs, Valve’s
engineers went out of their way to support different speaker
configurations. In Half-Life 2, the in-game sounds and
dynamic music have been mixed to support two-channel,
four-channel, 5.1, and headphone setups. As a result, you’ll
get sound that’s specifically tuned to your configuration.
Loads of small positional sound effects effectively immerse
you in the game. For example, when something on one side
of your body makes an extremely loud noise—say a grenade
explosion—you lose hearing on that side for a few seconds.
And the Winner for
Audio Excellence is...
Half-Life 2’s audio engineers recorded multiple sounds for shattering
glass. Every time you plink a shot off at a window, you get a slightly
different sound. You’ll find yourself shooting glass and destroying
crates just for the fun of it.
When you play Half-Life 2, you may
notice that the animations for all
the character models—friend and
foe—look much better than those
in a standard first-person shooter.
Particularly impressive are visual
sequences where enemies are mov-
ing in one direction while simultane-
ously shooting in another direction.
The Source engine accomplishes this
trick with a technique known as ani-
mation blending.
Let’s use our favorite character, the
resistence fighter shown to the right,
as an example of how this technol-
ogy works. This stalwart fighter has
numerous animations for moving in
different directions and shooting in
different directions. Assume he has
four running animations: forward,
backward, to the right, and to the
left (this is a simplification, but not
a gross one). When he runs forward,
the engine cues the run-forward
animation, which is simple enough.
But there’s no animation for running
diagonally! Here’s where anima-
tion blending comes into play. If the
soldier needs to run diagonally, the
engine blends the “run sideways” and
“run forwards” animations, achieving
the desired effect.
What’s more, when our soldier is
running diagonally, he can still shoot
his weapon to the right by blending
the “shoot forward” and “shoot to the
right” animations with the two running
animations we talked about earlier.
In terms of practical gameplay, ene-
mies who can strafe and dodge while
they lay down suppressing fire at the
same time create much more challeng-
ing battles than the oft-used alterna-
tive: hordes of enemies who charge
right at you with guns blazing.
Model Behavior
This “Let’s kick some ass!” scowl is the result
of more than 40 bones in the character’s
face that have been hand-animated to convey
emotion. Interestingly, the Source engine also
uses a separate, unique lighting model for
human faces. This gives them a healthier glow,
and makes them look more realistic.