[JAVA][Beginning Java 8 Games Development]

Chapter 5 ■ An Introduction to Game Design: Concepts, Multimedia, and Using Scene Builder
Converting Analog Audio to Digital Audio Data: Sampling, Accuracy, HD Audio
The process of turning analog audio (sound waves) into digital audio data is called sampling. If you work in the
music industry, you have probably heard about a type of keyboard (or even rack-mounted equipment) called a
sampler. Sampling is the process of slicing an analog audio wave into segments so that you can store the shape of
the wave as digital audio data, using a digital audio format. This turns an infinitely accurate analog sound wave into
a discrete amount of digital data, that is, into zeroes and ones. The more zeroes and ones used, the more accurate the
reproduction of the infinitely accurate (original) analog sound wave.
Each digital segment of a sampled audio sound wave is called a sample, because it samples that sound wave at an
exact point in time. The sample accuracy (resolution) you want will determine how many zeroes and ones are used
to reproduce analog sound waves, so the precision of a sample is determined by the amount of data used to define
each wave slice’s height. As with digital imaging, this precision is termed the resolution, or, more accurately (no pun
intended), the sample resolution. Sample resolution is usually defined using 8-bit, 12-bit, 16-bit, 24-bit, or 32-bit
resolution. Games mostly leverage 8-bit resolution for effects such as explosions, in which clarity is not as important;
12-bit resolution for crystal-clear spoken dialogue and more important audio elements; and, possibly,
16-bit resolution for background music.
In digital imaging and digital video this resolution is quantified by the number of pixels, and in digital audio,
by how many bits of data are used to define each of the analog audio samples taken. Again, as with digital imaging,
in which more pixels yields better quality, with digital audio a higher sample resolution yields better sound
reproduction. Thus, higher sampling resolutions, using more data to reproduce a given sound wave sample, will
produce higher-quality audio playback, at the expense of a larger data footprint. This is the reason that 16-bit audio
(commonly referred to as CD quality audio) sounds better than 8-bit audio. Depending on the audio involved, 12-bit
audio can be a great compromise.
In digital audio there is a new type of audio sample, known as HD audio in the consumer electronics industry.
HD digital audio broadcast radio uses a 24-bit sample resolution, so each audio sample, or slice of the sound wave,
contains 16,777,216 bits of sample resolution. Some of the newer hardware devices now support HD audio, such as
the smartphones you see advertised featuring “HD-quality audio,” meaning that they have 24-bit audio hardware.
These days, laptops (including PCs), as well as game consoles and iTVs, also come standard with 24-bit audio
playback hardware.
It is important to note that HD audio is probably not necessary for Java 8 games, unless your game is music
oriented and makes use of high-quality music, in which case you can use HD audio samples via a WAVE file format.
Another consideration is digital audio sampling frequency (also called the sampling rate), This is a measure
of how many samples at a particular sample resolution are taken during 1 second of sampling time frame. In terms
of digital image editing, sampling frequency is analogous to the number of colors contained in a digital image. You
are probably familiar with the term “CD-quality audio,” which is defined as using a 16-bit sample resolution and a
44.1kHz sampling rate (taking 44,100 samples, each of which has 16 bits of sample resolution, or 65,536 bits of audio
data). You can determine the amount of raw data in an audio file by multiplying the sampling bit rate by the sampling
frequency by the number of seconds in the audio snippet. Obviously, this can potentially be a huge number! Audio
codecs are really great at optimizing data down to an amazingly small data footprint with very little audible loss
in quality.
Thus, the exact same trade-off that exists in digital imaging and digital video occurs with digital audio as well:
the more data you include, the higher quality the result, but always at the cost of a much larger data footprint. In the
visual mediums the size of the data footprint is defined using color depth, pixels, and, in the case of digital video and
animation, frames. In the aural medium it is defined via the sample resolution, in combination with the sampling
rate. The most common sampling rates in the digital audio industry currently include 8kHz, 22kHz, 32kHz, 44.1kHz,
48kHz, 96KHz, 192kHz, and even 384kHz.
Lower sampling rates, such as 8kHz, 11kHz, and 22kHz, are the ones that you are going to use in your games, as,
with careful optimization, these can yield high-quality sound effects and arcade music. These rates would be optimal
for sampling any voice-based digital audio as well, such as movie dialogue or an e-book narration track. Higher audio
sample rates, such as 44.1kHz, would be more appropriate for music, and sound effects that need a high dynamic
range (high fidelity), such as rumbling thunder, could use 48kHz. Higher sample rates will allow audio reproduction
that exhibits movie theater (THX) sound quality, but this is not required for most games.
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