Game Development Reference
performance. This is where a different form of compression comes
in very handy.
ADPCM is a lower level of compression and sounds much closer
to the source audio than an MP3. As you can see from Fig. 8.2 ,
a one-second sound file that was 44 k in size becomes just 11 k,
using a sample rate of 22 kHz and a bit depth of 4. Not only is this
very small, but also it will cause far less overhead in the Flash Player.
OBSESSING OVER SOUND QUALITY
I tend to like to tweak the sound properties throughout the course of a project.
Sometimes, a compressed sound will be noticeable garbled or distorted, when
played by itself, but in the context of all the other sounds, it works fine. The
opposite is also sometimes, true. I
ve often found that for short sound effects
that exist in within a specific frequency range (beeps, clicks, and so on), you
can even get away with lowering the bit depth to three without a noticeable
difference, and squeeze out a few extra kilobytes. Your mileage may vary.
There is one other setting that is useful, specifically, for voice-
over sounds: Speech. It has no options to set other than a sample
rate (22 kHz is usually fine), and is a special variant of MP3 com-
pression designed by Adobe to work best with a human voice. It
also exports relatively quickly and doesn
overhead of a regular MP3.
If you only have a few sounds in your game, or you know most
of your sounds are of the same type and will use the same form of
compression, you can leave the individual sound properties set to
Default and change them globally in the Publish Settings. You
most interested in the Audio Event settings; Audio Stream isn
Figure 8.2 For sound effects,
ADPCM is the best option for