Game Development Reference
In-Depth Information
takes twice as much space to store but provides left and right channel waveforms.
The different frequencies and bit depths have an interesting and quite drastic effect
on the sound.
Digital audio is created by sampling a waveform and converting it into discrete 8- or
16-bit values that approximate the original waveform. This works because the human
ear has a relatively narrow range of sensitivity: 20Hz to 20,000Hz. It
s no surprise
that the common frequencies for storing WAV files are 44KHz, 22KHz, and
11KHz.
It turns out that telephone conversations are 8-bit values sampled at 8KHz, after the
original waveform has been filtered to remove frequencies higher than 3.4MHz.
Music on CDs is first filtered to remove sounds higher than 22KHz and then sam-
pled at 16-bit 44KHz. Just to summarize, Table 8.3 shows how you would use the
different frequencies in digital audio.
Use lower sampling rates for digital audio in your game to simulate telephone con-
versations or talking over shortwave radio.
'
Animated sequences in games go as far back as Pac Man, where after every few levels
you
d see a little cartoon featuring the little yellow guy and his friends. The cartoons
had little or nothing to do with the game mechanics, but they were fun to watch and
gave players a reward and a short break. One of the first companies to use large
amounts of video footage in games was Origin Systems in the Wing Commander
series. More than giving players a reward, they actually told a story. Epic cinematics
are not only common in today
'
s big-budget games, but they are also expected.
There are two techniques worth considering for incorporating cinematic sequences.
Some games like Wing Commander III will shoot live video segments and simply
'
Table 8.3 Using Different Audio Frequencies with Digital Formats
Format
Quality
Size per Second
Size per Minute
44.1KHz 16-bit stereo WAV
CD quality
172KB/second
10MB/minute
128Kbps stereo MP3
Near CD quality
17KB/second
1MB/minute
22.05KHz 16-bit stereo WAV
FM Radio
86KB/second
5MB/minute
64Kbps stereo MP3
FM Radio
9KB/second
540KB/minute
11.025KHz 16-bit mono WAV AM Radio
43KB/second
2.5MB/minute
11.025KHz 8-bit mono WAV
Telephone
21KB/second
1.25MB/minute
