658 APPENDIX A: Audio Concepts, Terminology, and Codecs
Thus, the initial process for optimizing your digital audio assets across all of the Android devices is
going to be to create 16-bit assets at 44.1kHz and 48kHz, and then optimize (compress) them using
the different formats supported in Android. Once that process is completed, you can then see which
digital audio assets provide the highest quality digital audio playback in conjunction with the lowest
possible data footprint.
You will do this by using the latest version of the open source Audacity 2.0.5 digital audio editing and
engineering software package. This software package is freely available on SourceForge.net, and
is accessible to all readers, no matter which OS platforms they prefer, whether it be Windows 8.1,
Macintosh OS/X, or SUSE Linux.
Audio Sequencing: Concepts and Principles
Recall that the earliest forms of digital audio sequencing actually utilized MIDI.
MIDI sequencers such as the Rosegarden software mentioned earlier are still popular, and allow
performance data sequencing. This is where a composer plays each instrumental part into a
computer using a synthesizer set to use a given instrument sample, say a guitar, bass, or piano
sample, and then the computer plays back this performance data later on, while the composer
accompanies the computer-replayed version of that performance.
Eventually MIDI sequencing software added digital audio capabilities alongside MIDI playback
capabilities, as increased computer processing power, as well as specialized digital audio adapters,
such as Creative Labs’ X-Fi, became available to consumers at affordable prices. It turns out
that this concept of audio sequencing is applied equally well to digital audio samples that are
manipulated directly by a computer, as long as this computer is powerful enough. My Samsung
Galaxy Note 3 has a 2.3GHz Quad-Core processor, so that time has certainly arrived!
Computers—in this case, Linux-based Android devices—keep getting more and more powerful, and
are featuring four to eight processor cores, and one, two, or even four billion bytes of system memory.
This means that Android devices can hold several digital audio samples in memory, and this memory
optimization is an issue with Android SoundPool, as you will soon see. I wanted to cover SoundPool,
an admittedly advanced audio sequencing engine class in Android, in this book, even though this
book is for “Absolute Beginners.”
The reason for this is because if you want to utilize digital audio assets in your application, especially
using samples or audio snippets, rather than just playing back songs, SoundPool is the way to go.
Digital Audio Synthesis: Concepts and Principles
Some of the very first MIDI keyboards were digital audio samplers. These played back digital audio
samples, pre-recorded (sampled) by digital audio sample design professionals like Frank Serafine,
using a range of sample resolutions and sample frequencies.
You learned about samples in a previous section in the Appendix, so what you are going to focus
on here is how those samples are taken to the next level using audio synthesis (via algorithmic
processing). Synthesizers can also apply these algorithms to raw waveforms, such as sine, saw,
or pulse waves.