MACROMEDIA Director MX, Руководство пользователя

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Sound and Synchronization 325
About Shockwave Audio
Shockwave Audio is a technology that makes sounds smaller and plays them faster from disk or
over the Internet.
Shockwave Audio can compress the size of sounds by a ratio of up to 176:1 and is streamable,
which means Director doesn’t have to load the entire sound into RAM before it begins playing.
Director starts to play the beginning of the sound while the rest of the sound is still streaming
from its source, which can be from a disk or over the Internet. When used properly, the
Shockwave Audio compression and streaming features provide fast playback of high-quality
audio, even for users with relatively slow modem connections to the Internet.
Compression quality in Shockwave Audio
Although Shockwave Audio uses advanced compression technology that alters original sounds as
little as possible, the more a sound is compressed, the more it is changed.
Set the amount of compression by selecting a bit rate setting in any of the Shockwave Audio Xtra
extensions. The bit rate is not related to sampling rates you might have used in other audio
programs. Try compressing the same sound at several different bit rates to see how the
sound changes.
Select the bit rate that is appropriate for the intended delivery system (modem, ISDN, CD-
ROM, hard disk, and so on), the type of movie, and the nature of the sound. Voice-over sound
quality, for example, might not need to be as high as that of music. Test the sound on several
systems to find the right balance between quality and performance.
The more compressed a sound is, the faster it streams. If you select to use a high quality and low
degree of compression, a slow delivery system might not send the data fast enough, which results
in gaps during playback. Most developers choose 16 kilobits per second (Kbps) for the best results
over the Internet.
The following table suggests some general guidelines for setting the bit rate for different delivery
systems. It also provides a rough estimate of perceived quality for different rates of compression.
Real transmission times might be slower than the times that are shown in this table, depending on
network traffic and server load.
Note: Any sound compressed at less than 48 Kbps is converted to monaural.
Delivery Bit rate Quality
T1 64 to 128 Kbps Equal to source material
ISDN or CD-ROM 32 to 56 Kbps FM stereo to CD
28.8 modem 16 Kbps FM monaural or good-quality AM
14.4 modem 8 Kbps Telephone