This thread has grow over time and contains quite a lot of information. To make it easier to find specific information on this thread I have implemented a contents system which will allow you find information quickly. The thread has been split into sections and sub sections where appropriate. The contents uses Anchor points (thanks jimco for the tip!), so you can simply click on the section in the contents to jump to the section in the thread.
If you haven't followed this thread through various developments since it was first published, take a second to read this summary. This thread has expanded massively overtime, so the information in its entirety might be difficult to take in without knowing all the facts.
The original problem described in this thread is regarding latency spikes over WiFi on the XPS 15z. The latency spikes are caused by unknown factors which have never been truly pin pointed to any certain area (and still haven't to this day). There are many areas which have been highlighted including Windows 7 and its lack of process interruption protection, Intel WiFi Drivers, Realtek Sound Drivers and other areas. A lot of community activity was involved in trying to get to the bottom of this problem. It was eventually discovered that the Atheros Ethernet Adapter could be attributed to the problem, after a newer Non Dell OEM driver was found for the Atheros 815X Family Ethernet Controller on a third party website. This driver was tested by several community members and it was found that latency spikes were reduced heavily. Since this point, it has been a community recommendation to install the Qualcomm Atheros drivers rather than using the outdated Dell OEM driver which is dated May 2011 for the Ethernet card in the XPS 15z.
There is far more to the situation than this, but it is a summarized version of the events that have taken place over the months. If you don't know what DPC Latency is or are unfamilar with the problem being described, take a moment to read through this thread, it is seperated into logical headings and groupings to make it easier to pick out the key information.
It is important to note that while the use of the official Qualcomm Atheros driver over the Dell OEM driver has helped people in this situation it is not a guarantee that it will solve you problem. Sadly many factors can cause latency spikes, the Atheros Ethernet Controller seems to be just one of them.
To understand DPC latency, its important to first understand what the two terms mean on there own:
A Deferred Procedure Call (DPC) is a Microsoft Windows operating system mechanism which allows high-priority tasks (e.g. an interrupt handler) to defer required but lower-priority tasks for later execution. This permits device drivers and other low-level event consumers to perform the high-priority part of their processing quickly, and schedule non-critical additional processing for execution at a lower priority. - http://en.wikipedia.org/wiki/Deferred_Procedure_Call
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts. - http://en.wikipedia.org/wiki/Latency_(engineering)
When there is high latency various problems can occurs, one of the main issues that are a side effect of badly managed DPC latency is audio problems. This can be often seen with multimedia content like music or video. When you have bad latency you will experience drop outs and degraded audio. To see the problem visually you can use a DPC latency analysis program which will tell you when you have bad latency.
What causes high DPC latency?:
Here lies the million dollar question, many factors can cause high latency. In a lot of cases it is usually down to poorly written hardware drivers that don't perform quick enough and cause lag between process execution. This then creates high latency and then will interfere with running processes. Sometimes this can occur very rarely and is acceptable in some cases, however it becomes problem if the DPC latency constantly spikes and can be reproduced in certain scenarios.
For the specific case of the XPS 15z, the driver that seems to be the most problematic is the Dell OEM driver for the Atheros 8151 Ethernet Controller, it is difficult to pin point causes of high latency, but the problem has been attributed to it. That is not to say that the Ethernet controller is totally blame. Without Dell investigating there own driver/hardware implementations we can't even conclusively pin point the issue.
The bottom line of the situation is however, the XPS 15z has very high DPC latency in a lot of scenarios.
Disclaimer: These drivers are NOT official Dell OEM drivers and hence not certified by Dell. They are the OFFICIAL drivers from Qualcomm Atheros but have not been compiled specifically for Dell OEM. It is 100% safe to use these drivers, but if you experience any problems, roll back to the Dell OEM driver. It is likely Dell won't help you if you have problems with your Ethernet Controller when using these drivers.
After community testing of a newer 2.0 release of the Non OEM Atheros Driver found by Dell Community User richsark it has been found that the non OEM drivers certainly help the situation a great deal with regards to the latency issue. So if you having problems described in this thread, try following the Qualcomm Atheros driver installation steps in this section.
Another Dell Community member JimK157 has found Qualcomm Atheros have been releasing newer drivers for certain Atheros Ethernet Controllers on a regular basis, the AR815X Family Drivers which is what the XPS 15z has is part of these releases. The good news about this is there is now a dedicated page for these drivers which can be tracked:
If you are already comfortable with updating drivers manually through device manager you can go ahead and download the drivers and manually install them, if you aren't sure what to do, follow these instructions:
In the extracted driver folder there is a setup.exe, however due to this being the generic Qualcomm driver and not Dell OEM it is strongly recommended you only install the driver and nothing else. to avoid any performance issues or problems.
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.
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.
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.
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:
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:
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:
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.
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.
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.
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.
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.
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:
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!
I have this problem on mij xps15 . when i copy files to mij other laptop on the network its inpossible to play mij music .
even when i browse mij laptop or checking the internet the sound crackels an sometimes it's completley miss formed while i open a folder in mij
music library .
the best thing to do is to send mij laptop back to dell ? its only 1 month old .
Thank you for this post. I have been communicating with ShonkyCH from a different forum (attached at the end of this post) to try and get this resolved. Like ShonkyCH, I too had the Centrino 6230 replaced. In my case, the WiFi card was replaced WITH A NEWER REVISION of the same card. Unfortunately, the problem persists so I am stuck with this issue until it's potentially resolved with a driver update.
I have also contacted a Dell rep ("Terry-B") on the Dell Forums who put in the request for my repair. He said that engineering believes that Windows 7 doesn't protect real-time audio, which is the primary cause for the crackling audio. ShonkyCH and I believe otherwise. We believe that this is either a software or design issue with the 15z.
I am going to ask Terry-B if Dell plans on releasing a new driver anytime soon. At the moment, they have not made any mention of this.
iAMjason, thanks for your reply. I have actually been monitoring the thread over on the Notebook Review Forum which lead me to do an in depth write up on the latency issue on these forums for document purposes and to make sure Dell were aware of this issue as I was truly shocked the wireless card has such massive latency spikes as shown above.
Its interesting to find out that a newer revision of the Centrino N card still has the same problem, this find may lend credibility to the fact that this is a driver issue. I haven't searched extensively but I haven't seen this problem reported on any non Dell laptop, so I don't think its a general hardware problem, but I can't be sure without any official word from Dell/Intel.
Linking Terry-B to the thread over at the Notebook Review Forums and possibly this one should help you get somewhere, as we have plenty of evidence of the underlying problem and many XPS 15z user testimonials that cite the Wireless card as the problem.
Looks like there is a BIOS update (A09) released on the 2nd Feb for XPS 15z
Couldn't find any changelog as to what it adjusts/fixes, but its out there for anyone interested.
No, it's not.
Really I'm very frustrate with dell now this they called premium product wow premium my foot. Even you call dell support the first they are going to say you are the first customer who reporting this even they blame it's your router, Please don't call your self engineer holding a degree and when it's come to knowledge you engineer goes fiss..
Time to file online petition.
Terry-B has responded to my message regarding this issue. He acknowledges that there is a problem and has brought it to the attention of Dell's engineering team (though, I'm not exactly sure if that will result in anything significant). I will attach the conversation below for those monitoring this thread.
If Engineering is taking that stance, will they continue looking into this issue? I respect their answer, but if this problem is caused by Windows 7, couldn't this problem be replicated by EVERYONE who uses the 15z out-of-the-box? I know several other people with identical 15z's and have never heard the crackling audio from the day they got it.
Recently, another thread concerning this issue has been created on the Dell Forum. We believe that a driver update to the Centrino 6230 card can potentially resolve this issue. On behalf of myself and others who are still experiencing this issue, we would GREATLY appreciate if this forum was forwarded to Engineering. I have attached the link to the forum below.
Yeah that is a great post. I know some of the guys from engineering are taking a look at it. They still have not changed their stance on it yet and I have escalated this a couple of times. I will keep pointing out to them how disatisfied you all are. I wish that I had more for you now.
Regarding new drivers, there have been multiple drivers for the Centrino 6230 card since the XPS 15z has been released and I certainly suggest uninstalling and reinstalling the latest driver if you have not already done so.
I also know that Intel is working hand in hand with Dell regarding drivers for their centrino products and I expect new drivers are on their way although I have no ETA.
If these drivers are going to help with possible DPS latency issues I can't say. Engineering are aware of these posts.