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

1. Open Device Manager and expand the "Network adapters" menu
2. Right click on your Atheros AR8151 Ethernet Adapter. It's name may differ depending on your driver version. Newer driver versions display the name as "Qualcomm Atheros AR8151 PCI-E Gigabit Ethernet Controller (NDIS 6.20)" older driver versions will display the name differently.
3. Select Update Driver Software from the menu
4. Select Browse my computer for driver software
5. Now you will be asked to manually specify the location of the Ethernet driver. You will need to click browse to specify where you extracted the .rar archive to and navigate to this path Common_Dri\Win7_64 so device manager can locate the driver. When you have specified this path click OK and the driver will be automatically installed. If everything went OK device manager will state this in the window confirming a successful driver upgrade

To confirm the driver was updated to a newer version you can always compare the driver version/date to the previous version prior to updating. Making a note of the driver version/date is a good indicator.

4. 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.

5. EVIDENCE AND INFORMATION REGARDING THE WIRELESS LATENCY ISSUE

a. 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.

b. Evidence of latency spikes on the XPS 15z

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 2.4 Ghz (Single Band)
• NAS Server: HP ProLiant Microserver N36L (Integrated Broadcom Gigabit Ethernet Port, connected to a Gigabit switch)

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.

7. WORKAROUNDS/FIXES TO THIS PROBLEM

a. RECOMMENDED WORKAROUND:

Using the Qualcomm Atheros drivers for the Ethernet Controller seems to help a lot of people that experience large latency spikes in certain situations. You can find out how to obtain and install the Qualcomm Atheros driver by clicking here. From testing it has performed much better than the Dell OEM driver and has reduced latency spikes in most cases. It is not however the magic fix to the problem. Latency spikes still occurs, however they become far less common and not as severe. It has been tested by members of the community and has yielded good results, but again there are no guarantees of its success rate with different users.

b. LEGACY WORKAROUNDS:

Any workarounds here are classed as legacy workarounds as they are not as effective as the recommended workaround and have been hit and miss for a lot of people.

Creating a custom power plan:

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. 

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.

Hardware replacement/Wireless speed adjustment:

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.

8. 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.

A big thank you to everyone who has contributed to this thread. This thread stands today because of the community and everyone who helped test, contributed important information and shared there knowledge on the situation. Without the community this thread would not be as comprehensive as it is now. Well done everyone, this was truly a forum community effort to compile this information together!