I pulled this from creatives site, see if it will help.
SYMPTOMS
How to Effectively Configure AC-3 Decode
RESOLUTION
AC-3 or Dolby Digital 5.1 is a standard in digital audio compression. The main feature of this style of compression is its single stream coding for all 5 speakers (center, front left and right, and rear left and right) and an independent subwoofer. It has become a required format on DVD and DVD-Audio discs and has made an appearance in computer games. With a Sound Blaster audio card with 5.1 speaker compatibility and AC-3 decoding, such as the Sound Blaster Live 5.1 or the Sound Blaster Audigy, along with 5.1 ready speakers, there is the option to choose whether decoding takes place on the speaker receiver or on the sound card.
With the Sound Blaster Extigy, which is intended to act as the speaker receiver itself, AC3 decoding is always enabled.
In general, if the speakers being used are capable of decoding an AC3 signal, such as the DTT 3500s or the Inspire 5700s, and are connected to the Digital Out port on the soundcard, it is best to disable AC-3 decode on the soundcard and let the speakers/decoder handle the signal. This will take work away from the soundcard and the computer, permitting them to focus on other matters.
However, if the speakers being used are not capable of decoding AC3 signals themselves (for example the analog 5.1 speakers & Creative Inspire 5300), it is essential that the AC3 decoding be enabled so that the soundcard can decode the signal for the speakers.
Also, it should be noted that with AC3 decoding turned off, the soundcard will not apply effects or otherwise process the signal. Thus, if it is necessary to have environmental effects, or other special effects applied by the soundcard it will again be necessary to have AC3 decode enabled.
To change the AC3 decode options for the Sound Blaster Live 5.1, go to Start, Programs, Creative, Sound Blaster Live, Surround Mixer. In the Speaker Tab of the Surround Mixer, click on Settings. The check box to enable or disable AC-3 Decode will be in the lower portion of the Settings windows.
On the Sound Blaster Audigy, go to Start, Programs, Creative, Sound Blaster Audigy, Surround Mixer. In the Speaker Tab of Surround Mixer, click on Advanced. Check or clear the box next to AC-3 Decode to enable or disable AC-3 decoding
SYMPTOMS
How to Effectively Configure AC-3 Decode
RESOLUTION
AC-3 or Dolby Digital 5.1 is a standard in digital audio compression. The main feature of this style of compression is its single stream coding for all 5 speakers (center, front left and right, and rear left and right) and an independent subwoofer. It has become a required format on DVD and DVD-Audio discs and has made an appearance in computer games. With a Sound Blaster audio card with 5.1 speaker compatibility and AC-3 decoding, such as the Sound Blaster Live 5.1 or the Sound Blaster Audigy, along with 5.1 ready speakers, there is the option to choose whether decoding takes place on the speaker receiver or on the sound card.
With the Sound Blaster Extigy, which is intended to act as the speaker receiver itself, AC3 decoding is always enabled.
In general, if the speakers being used are capable of decoding an AC3 signal, such as the DTT 3500s or the Inspire 5700s, and are connected to the Digital Out port on the soundcard, it is best to disable AC-3 decode on the soundcard and let the speakers/decoder handle the signal. This will take work away from the soundcard and the computer, permitting them to focus on other matters.
However, if the speakers being used are not capable of decoding AC3 signals themselves (for example the analog 5.1 speakers & Creative Inspire 5300), it is essential that the AC3 decoding be enabled so that the soundcard can decode the signal for the speakers.
Also, it should be noted that with AC3 decoding turned off, the soundcard will not apply effects or otherwise process the signal. Thus, if it is necessary to have environmental effects, or other special effects applied by the soundcard it will again be necessary to have AC3 decode enabled.
To change the AC3 decode options for the Sound Blaster Live 5.1, go to Start, Programs, Creative, Sound Blaster Live, Surround Mixer. In the Speaker Tab of the Surround Mixer, click on Settings. The check box to enable or disable AC-3 Decode will be in the lower portion of the Settings windows.
On the Sound Blaster Audigy, go to Start, Programs, Creative, Sound Blaster Audigy, Surround Mixer. In the Speaker Tab of Surround Mixer, click on Advanced. Check or clear the box next to AC-3 Decode to enable or disable AC-3 decoding
