Computers can capture and encode digital audio—computer representation
of sound information—and can store it and retrieve it to play back
over speakers. You can play back sound using either Adobe® Flash® Player
or Adobe® AIR™ and ActionScript.
When sound data is converted to digital form, it has various
characteristics, such as the sound’s volume and whether it is stereo
or mono sound. When you play back a sound in ActionScript, you can
adjust these characteristics as well—make the sound louder, or make
it seem to be coming from a certain direction, for instance.
Before you can control a sound in ActionScript, you need to have
the sound information loaded into Flash Player or AIR. There are
five ways you can get audio data into Flash Player or AIR so that
you can work with it using ActionScript.
-
Load an external sound file such as an mp3 file into
the SWF.
-
Embed the sound information into the SWF file directly when
it’s being created.
-
Capture audio from a microphone attached to a user’s computer.
-
Stream audio from a server.
-
Dynamically generate and play audio.
When you load sound data from an external sound file, you can
begin playing back the start of the sound file while the rest of
the sound data is still loading.
Although there are various sound file formats used to encode
digital audio, ActionScript 3.0, Flash Player and AIR support sound
files that are stored in the mp3 format. They cannot directly load
or play sound files in other formats like WAV or AIFF.
While you’re working with sound in ActionScript, you’ll likely
work with several classes from the flash.media package. The Sound
class is the class you use to get access to audio information by
loading a sound file or assigning a function to an event that samples
sound data and then starting playback. Once you start playing a
sound, Flash Player and AIR give you access to a SoundChannel object. Since
an audio file that you’ve loaded may only be one of several sounds
that you play on a user’s computer, each individual sound that’s
playing uses its own SoundChannel object; the combined output of
all the SoundChannel objects mixed together is what actually plays
over the computer’s speakers. You use this SoundChannel instance
to control properties of the sound and to stop its playback. Finally,
if you want to control the combined audio, the SoundMixer class
gives you control over the mixed output.
You can also use several other classes to perform more specific
tasks when you’re working with sound in ActionScript; for more information
on all the sound-related classes, see
Understanding the sound architecture
.
Important concepts and terms
The following
reference list contains important terms that you may encounter:
-
Amplitude
-
The distance of a point on the sound waveform from the zero
or equilibrium line.
-
Bit rate
-
The amount of data that is encoded or streamed for each second
of a sound file. For mp3 files, the bit rate is usually stated in
terms of thousands of bits per second (kbps). A higher bit rate
generally means a higher quality sound wave.
-
Buffering
-
The receiving and storing of sound data before it is played
back.
-
mp3
-
MPEG-1 Audio Layer 3, or mp3, is a popular sound compression
format.
-
Panning
-
The positioning of an audio signal between the left and right
channels in a stereo soundfield.
-
Peak
-
The highest point in a waveform.
-
Sampling rate
-
Defines the number of samples per second taken from an analog audio
signal to make a digital signal. The sampling rate of standard compact
disc audio is 44.1 kHz or 44,100 samples per second.
-
Streaming
-
The process of playing the early portions of a sound file
or video file while later portions of that file are still being
loaded from a server.
-
Volume
-
The loudness of a sound.
-
Waveform
-
The shape of a graph of the varying amplitudes of a sound
signal over time.
