Article update log
- 16.03.2012: Added some quick tips to 4.Tips & tweaks in reducing DPC latency
- 11.08.2010 : Added Win 7 & Asio results to 3.1 chapter (draft version)
- 3.08.2010 : Part 1 (First Revision)
1. What is DPC latency.
“If any kernel-mode device driver in your Windows system is implemented improperly and causes excessive latencies of Deferred Procedure Calls (DPCs) then probably drop-outs will occur when you use real-time audio or video streaming applications” – http://www.thesycon.de/eng/latency_check.shtml
Basically if you are watching a movie and your computer has high DPC latencies, your audio/video will pause or skip for a couple of seconds. The same will happen with games.
The worst part is that those audio/video dropouts will occur regardless if you have a single core P4 2.4 GHz processor or a quad core Core i7. Bad coding of the drivers is usually the fault for high and very high DPC latencies.
2. How to check DPC latency
First you have to download and run the DPC latency checker from here. Note that DPC latency varies depending on the applications you are running (foreground and background). And it’s mostly influenced by audio data streams, video data streams and network activity (wireless, ethernet, bluetooth) . But that’s not all, for example mouse movement also causes DPC latency levels to rise. When you use a P2P application and you watch a HD 5.1 movie, this can lead to a very bad movie experience, audio/video desynchronizations occurring several times during playtime.
3. Test Setup & Some Examples
Lets start with the test system: Core 2 Duo 8400 3.0 GHz, DFI LP UT P35 motherboard,Marvell 1 GB Lan onboard, Realtek ALC885 audio onboard ,2×2 GB Ram, ATI HD 3870 video card, Asus Xonar DX sound card, Windows XP x64 (sp2), Windows 7 x64
3.1 Asus Xonar DX vs Realtek ALC885 showcase
The tests where done with 5.1 channel/44.1KHz settings except the cases where there are other settings specified . For comparison I also tested my on-board audio card Realtek ALC885 with Realtek HD 2.50 driver
Values are approximates . Values between 0-300 are good, 300-500 are OK, 500-1000 are bad and values >1000 are terrible.
Don’t compare Windows XP results with those of Windows 7. Windows 7 is a clean install where Windows XP is fully loaded with programs. After closing the programs that where running in the background, such as Rainmeter, the results for Uni Xonar low DPC latency on XP where 68 µs .
As you can see Realtek did a pretty good job with their drivers, the differences are enormous between Realtek and ASUS/C-MEDIA drivers with the same settings. For those of you who don’t know, I made a version of the Xonar drivers (Uni Xonar low DPC latency) which disables Asus Audio Center from startup, resulting in a lower DPC latency at ~120µs . This doesn’t mean that if you disable autostartup for Realtek Panel you will get better results. ASUS Xonar drivers are special and issues pop-up where they shouldn’t.
3.2 Network activity impact on DPC latency – showcase
Here are 2 examples where increased network activity rises DPC latency
a) µtorrent network usage: 10 KBps Download, 310 KBps Upload
b) µtorrent network usage: 4,5 MBps Download, 300 KBps Upload
4.Tips & tweaks in reducing DPC latency
16.03.2012 – Sorry guys as I never got around to do the part 2 the way I previously intended.
If you have problems with high DPC latency, here are some quick tips:
- Update your drivers (especially audio, network LAN, WiFi, Bluetooth, TV tuner) . Try searching for them on the original chip manufacturer and not on the motherboard manufacturers page.
- Disable unused components like LAN, onboard audio card, Bluetooth etc. via BIOS or Device Manager.
- Make sure you have your Windows updated
- Disable any motherboard/CPU monitors that autostart with windows (like GigaByte EasyTune, ASUS AI Probe and so on)
- Disable High Precision Event Timer (HPET) if you are using Windows Vista/7/8/10.
- Update your motherboard BIOS to the latest version.
A very good read in regards to updating drivers and different performance enhancements here (by Von Dach) .