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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, whether coming from 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 choosing a bit rate setting in any of the Shockwave Audio Xtras. The bit rate is not related to sampling rates you may have used in other audio programs. Try compressing the same sound at several different bit rates to see how the sound changes.

Choose the bit rate 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 itself. Voice-over sound quality, for example, may 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 choose to use a high quality and low degree of compression, a slow delivery system may not be able to send the data fast enough, resulting in gaps during playback. Most developers choose 16 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. Note that real transmission times may be slower than the times shown in this table, depending on network traffic and server load.

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

Note: Any sound compressed at less than 48 Kbps is converted to monaural.