XPS 15z Audio Crackling/Stuttering with network traffic over wireless (Latency Issue)

UPDATE 16/04/2012: POTENTIAL UNOFFICIAL FIX TO THIS PROBLEM:
NEEDS USER FEEDBACK! PLEASE REPORT BACK WITH YOUR RESULTS.

This is a potential unofficial fix to this problem which has been contributed by richsark, a big thanks goes to him for discovering and posting the steps on how to perform the fix. I have labelled this an unofficial fix as it has not been provided by Dell nor uses a driver certified by the Dell Driver Program. While the steps below are 100% safe to perform, it is important for technical and (possibly) legal reasons to highlight this point.

We would also really appreciate it if you would provide your feedback regarding the fix to let us know how this fix performs on different XPS 15z machines. To let us know, you can simply reply back to the thread with your results.

The fix involves actually updating the driver of the Atheros Ethernet Controller which is the AR8151 chipset in the XPS 15z. In earlier testing, this audio problem seemed to be wireless specific only, however it now does seem the Atheros Ethernet Controller does play a part in the problem, though it is still not 100% clear as to the exact cause.

1. Grab the driver from either of the following locations:
   
   http://www.x-drivers.com/catalog/drivers/ethernet/companies/atheros/models/ar8151/24975.html (Enter the spam prevention code to download) 
   
   http://dl.dropbox.com/u/73541048/Dell%20XPS%2015z/www.x-drivers.ru_atheros_ar813x_ar815x_v2.0.14.15.zip (Direct download from my Dropbox account)
   
   Either download location provides the same file, the dropbox link is an alternative location.
    
2. The driver will be in a zip format so you'll need to extract it with any archive extraction software
    
3. You will now have the unzipped folder contents. Within it  there will be loads of files. There is a setup.exe however due to this being a non-Dell driver, I'd advise you not to install it via the installer, instead the best way to do this is to install just the driver file only. To do this you first need to open up Device Manager and expand the Network Adapters option, right click on the Atheros Ethernet Controller and select disable (say yes to the prompt box that appears).
    
4. Now right click on the Atheros Ethernet Controller again and select Update Driver Software. Select the option Browse my computer for software manually, click on the browse button and point the location to the extracted folder of the Atheros driver .zip contents, you will then need to navigate to the subfolder Common_Dri\Win7_64. Click next and the driver will update itself. Once its done you will get a message saying the driver update was successful. To confirm the driver update worked your Atheros driver version should be now 2.0.14.15
   
   You have now updated the driver, now you can test it to see if audio problems have improved. From the small amount of testing performed so far, this updated driver does seem to help a great deal, running a latency test still shows red bars, but they have improved and don't spike as much. Audio playback also seems to be improved quite a bit. If you have performed this fix, please do let us now how its working for you, we need as many people as possible testing this fix so we can get an idea of how this fix is working for different XPS 15z owners.
   
   

IMPORTANT INFORMATION BEFORE REPLYING IN THIS THREAD:

Before replying to this thread make sure you are reporting the right problem. It has become apparent that the Dell XPS 15z has different audio problems which have caused some confusion in multiple threads. This specific thread is for people that are having problems with audio when using the WIRELESS connection, which happens to be related to DPC LATENCY.

If you experience problems with audio when using the Ethernet connection or a different scenario, do not post in this thread, you have a different problem. We are trying to keep the different audio issues separate, so Dell and other community members can understand the different issues.

Remember, this thread is for audio problems when using the XPS 15z over wireless only where massive latency spikes occur as shown below:

Please Note: Disabling the Atheros Wired adapter does not solve this problem, this suggestion is for a different problem but will make no difference to the problem described in this thread.

SUMMARY OF THE WIRELESS LATENCY PROBLEM

To summarise previous threads, many community members from the Dell Community and other forums have reported audio issues on the Dell XPS 15z for a while. This specific audio issue is regarding the Intel Centrino 6230 N Wireless Card in the XPS 15z.

When a wireless connection is active and network traffic is generated, audio glitches will occur on the XPS 15z. These glitches range from audio crackling, degradation and even audio playback being distorted. In some cases this issue can go unnoticed, however the underlying problem is always present.

EVIDENCE OF LATENCY SPIKES ON THE CENTRINO 6230 N

From reading various articles and other forum threads on this issue, I am pretty certain it is something to do with Wireless. Dell has stated in the past that the Centrino 6230 N card is not at fault for the audio issues, however I believe they are wrong.

Thanks to another community member (ShonkyCH), we have pretty hard evidence that the wireless card is causing these issues. If you observe the DPC latency on the Dell XPS 15z while on wireless you will find that you get very large spikes when an average amount of network traffic is generated. First some evidence of the problem:

EXHIBIT A: Performing a Latency test in real time.

The video below demonstrates the problem in real time. In this test I performed a simple action of the typical home user, by pulling a 720p Movie File from my NAS server. To make everything fair, here are the variables in this test:

• Router: WNR3500L V1, running DD-WRT K.26 Build 14929
• Wireless Speed: Wireless N (Single Band)
• NAS Server: HP ProLiant Microserver (Integrated Gigabit Ethernet Port, connected to a Gigabit switch)
• Transfer Rate over Wireless on LAN: Roughly around 20/30 Mb/s.

If you cannot play the embedded video click here to view the video directly.

The latency graph explained:

From the video above you have observed latency spikes when a decent amount of network traffic is generated. Below is more information on the latency test I performed.

Bar chart graph key:

• Green Bars - Good
• Yellow Bars - OK
• Red Bars - Bad, will cause audio drop-outs

Latency when network traffic is generated:

The next screenshot below shows the latency when network traffic is generated. Exactly the same test was performed as seen in the video to produce these results:

As you can see the latency is completely spiking off the scale. This was taken after I let the film play for a few minutes.

What this means in graph form is a visual representation of why the audio issues are happening. These latency spikes are (I believe) the primary contributor to the following audio issues users are having:

• Audio crackling (Constant under network load)
• Audio quality being degraded (Occurs in some cases)
• Audio playback plays as if the speed was being slowed. (Briefly happens, generally when using an Internet browser. It seems certain processes affect audio playback)

First of all you need to be on a Wireless connection only. Any wireless connection will do. It can be any speed either G or N. Then you can do a couple of things to see if you have the latency problem reported above. The easiest way would be to download a DPC Latency Checker program and observe the latency for yourself when you generate network traffic.

1. Download the DPC Latency Checker Program used in this test (http://www.thesycon.de/deu/latency_check.shtml)
2. Save it to a easily accessible location on your XPS 15z i.e. Desktop, Downloads Folder etc.
3. Go to the location you saved the download and open the executable dpclat.exe (It doesn't require an install it is a pre-compiled program)
4. Close any network related programs like Internet Browsers, Torrent Applications etc and let the program analyse your DPC latency.
5. Now generate network traffic, visit some websites in your favourite Internet Browser, perform general internet activities. If you have a NAS server (or similar setup) you might also want to perform the test above to see for yourself.

Another simple test to actually hear the audio glitches is to open your favourite music player i.e. Windows Media Player, iTunes, Zune, VLC etc and play some tracks in your playlist, now do some internet related activities, browse some web pages, just do some general normal day to day internet related actions. In a lot of cases you will find as you browse different web pages the audio of your music tracks playing becomes degraded, in most cases you will find either the audio crackles or the audio seems to slow down as if the speed of it was slowed by 2x, then once whatever browsing activity has finished the audio will be fine again. This happens with both the XPS 15z speakers and with headphones directly plugged into the headphone jack.

It is important to point out that the Ethernet Connection does NOT suffer the same DPC latency spikes and no such audio issues occur with anything network related over ethernet. Latency is far better and you will mainly find Green bars, with a few yellow bars, no red however.

WORKAROUNDS/FIXES TO THIS PROBLEM

16/04/2012: An unofficial fix has been proposed which is at the top of this thread, it involves updating the Atheros Ethernet Controller driver.

08/02/2012: A workaround has been found thanks to AKTundra. This workaround involves creating a custom power plan in Windows 7 with a couple of modified settings related to processor power management.

Creating a custom power plan:

1. In your Taskbar (Bottom Right) right click on your battery icon and select power options. If you don't have system icons enabled you can access the power options via Control Panel. i.e. Start > Control Panel > Hardware & Sound > Power Options
    
2. The power options window will appear, on the left hand side select create power plan.
    
3. Give your power plan a name e.g. Audio Fix, you can base it off either Balanced or High Performance you can also leave the on battery/plugged in settings on their default values. Click create to create the new power plan
    
4. The power plan you just created should be now in the Select a power plan menu. Find it and then click "Change Plan Settings" then click "Change advanced power settings".
    
5. A smaller window will now appear with the option of changing more advanced power plan related settings. Scroll down to "Process power management" and expand the menu, now expand the "Minimum processor state" option. There will be two values, on battery and plugged in. By default these will read 5%, you will need to change both to either 50% or 55%. Once the values have been changed click apply and click OK to close the advanced options window. You may have to increase these values further depending on your environment and setup.

OTHER WORKAROUNDS:

One solution that has been documented by ShonkyCH is getting the wireless card replaced. He had his wireless card replaced by Dell which ended up being a Dell branded Broadcom based device. The good news was it fixed the problem, the bad new is the replacement card lacks several features of the Centrino 6230N and hence isn't really a great solution. I personally won't accept this as a fix and hence continue to keep various threads regarding audio issues on the XPS 15z alive until I get some acknowledgement from Dell for everyone in the same boat regarding audio issues.

An interesting point that was discovered through experimentation is it seems latency issues seem to be more of a problem when on higher speed networks. E.g. Wireless N compared to Wireless G. A few people reported audio issues occur far less when on a Wireless G network compared to a Wireless N, where throughput is far less, however Wireless G speeds still produce latency spikes contributing to audio issues.

A final (last resort) workaround is to use Ethernet if possible. This obviously isn't a solution, but if you have access to an Ethernet port at Home/Work try and use it. I know, its not a great solution, but you might have to compromise for now until this problem is sorted.

WHAT IS DELL'S COMMENT ON THIS PROBLEM?

A few of us have privately messaged moderators on this forum and/or contacted Technical Support about this issue and have received the following comments, here's a summary of what Dell have said about this issue:

• Engineering state its a Windows 7 problem, due to lack of processing interruption protection
• They do not believe the Centrino 6230 N is at fault.
• Technical Support agents don't except the problem either and have even blamed networking hardware such as the customers router.
• Dell agents have scheduled service calls changing pieces of hardware of a few community member's XPS 15z including Motherboard, Speakers and Wireless card. All replacement Centrino Wireless card variants have had the same problem, speaker/motherboard replacements have been ineffective.