Exerpt from Creative Forums: Direct link to page at https://forums.creative.com/t5/Sound-Blaster/Static-noise-from-soundcards-encountered-with-Nvidia-dual-SLI/m-p/521634

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03-09-2009 08:06 PM - last edited on 05-07-2009 02:05 AM

Dear Sound Blaster users,

Static noise from soundcards encountered with Nvidia dual SLI graphic configurations

We have received feedback from many of our users regarding distortion  with Nvidia graphics card in SLI configuration.  The typical setup that we hear from feedback is Nvidia nForce SLI motherboard and 2 Nvidia graphic cards in SLI mode. Common feedback is audio distortion while playing trailers / videos, especially High Definition versions, audio popping and severe crackling while playing certain games, and audio distortion when DTS Connect or Dolby Digital Live! is turned on.

Other users have reported crackles when there is some sort of disk activity like copying and downloading large files and defrag. Most of the systems affected are SLI- boards with SATA drivers Raid enabled. Also mentioned are devices that really stress bus bandwidth like SCSI controller cards and the SkyStar2 DVB-S PCI TV Tuner card.

In our investigations we were able to reproduce some of these problems.  We have not seen this issue with the Intel X58 SLI Enabled motherboard that was launched recently. 

We have found that when this distortion occurs, the Sound Blaster X-Fi audio transport encounters severe cache/FIFO underflows and crackles are heard. This occurs if the audio card's accesses to host memory are denied for long periods of time, more than what the audio chip can gracefully handle. Typically this happens during intense graphics activity such as playing games/movie etc.

We also noticed in such cases, Sound Blaster X-Fi's requests for PCI bus service are being "retried," or deferred, an extraordinary number of times, presumably while the graphics system is using system memory.   The Sound Blaster X-Fi sound card can withstand up to about 450 bus retries on occasion, but in these cases we are sometimes seeing over 8000 bus retries for a single request (to system memory to read audio data to play), for a total deferral time of up to 2 milliseconds (240 nanoseconds per retry).  We have seen these deferrals cause audio defects in non-Creative PCI sound cards as well.  This problem is specifically related to the system so we do not have a definitive solution for this problem, but here are some possible mitigations:

1) In some cases using 2G of dual-channel memory mitigates the problem. Users are advise to refer to their motherboard manual to set the optimum configuration for their system RAMs.
2) Flashing the BIOS or changing CMOS can cause the memory and PCI performance to improve or sometimes degrade.  We do not know of any particular BIOS versions that are better or worse, but flashing the BIOS can cause the system memory resource allocation to change.
3) From the forum, users have reported that sometimes removing one SLI graphics card, rebooting with X-Fi, then shutting down and reinstalling the second graphics card fixes the problem

The use of two PCI-express graphics cards together to render the same image (SLI mode) means that access to system RAM will be delayed.. and together the two cards are using x16 PCIe!  Thus, the system RAM bandwidth is strained  by what is effectively a 32-lane PCIe graphics card.   If the system de-prioritizes PCI requests relative to other peripherals like SATA HD's or PCI-e graphics cards, the Sound Blaster X-Fi will not get the bandwidth  it needs in time.

Motherboard manufacturers sometimes configure their systems this way so as to boost their performance numbers while saving cost, not realizing that not all PCI  peripherals can handle being held off on the bus to such an extent.  And we are not able to increase our buffer sizes because of audio latency restrictions.

We have contacted Nvidia directly last year, with the intention of resolving these issues.  This bug was logged with NVidia several months ago. Unfortunately, to date we have not been able to get any positive or active response despite having sent several mails.

In the course of our investigations, we also found the following:-

a.    SLI audio issues are not just specific to Creative audio cards. Non Creative cards also encounter distortions.
b.    Not all SLI setups will have audio problems.  If SLI mode is disabled, the distortion goes away.  We encounter distortions on 280 GTX SLI on XFX 790i Ultra Motherboard (Nvidia 790i Ultra chipset, but there were no distortions on Asus Rampage 2 Extreme (Intel X58 chipsest)
c.   Driver upgrades do help mitigate the problem.  Bad crackling occurred when playing Crysis and Bioshock, using XFX 790i Ultra Motherboard chipset driver ver 9.64 with 9800 GX2 SLI video card driver ver 178.24. Crackling was much reduced when using the latest XFX 790i Ultra Motherboard chipset driver ver 15.23 with 9800 GX2 SLI video card driver ver 182.06.

We understand the frustrations of users not being able to enjoy their movies and games.  While it is unfortunate that we are not able to help fix the problem, we hope that the above information will help shed light on the issue and help users make a better informed decision.  We will continue to work to find a solution to provide the best audio experience for our users, and we welcome user feedback as it is impossible for us to test all possible configurations.

Thank you,
The Sound Blaster Team

Update: There is an announcement and a beta driver released to address the issue. Read this post for more details.