DPC latency – yet another nightmare
It wouldn't be that fun if a musician recording on Windows platform didn't wake up with 165 BPM heartbeat from nightmarish dreams. Well, Microsoft definitely enjoys making our life more complicated and if you don't like audio latency, you will hate DPC one for sure!
There are times when I wish I wasn’t so addicted to Cakewalk’s Sonar audio workstation software. As Sonar is released just for Windows, I can’t take it elsewhere (onto Mac for example). And as a Windows user I have to solve a lot of problems when recording. The main problem is the latency.
For a long long time I have known about audio latency (which can be resolved to some extent by ASIO drivers) but a couple of months ago I happened to read something about DPC latency. I didn’t pay attention that much at the time, thinking it was not my problem, although the article reminded me fighting with Line6 UX2 and POD Farm and repeated crackles I heard when playing the guitar. Then Dell released a new BIOS upgrade for my laptop with description “1. Added Win7 support. 2. Fixed DPC Latency”. What? No way! Well, yes way…
What DPC latency is?
DPC stands for Deferred Procedure Call meaning that different hardware drivers on your computer request processing power of computer’s CPU (processor) to deal with particular tasks. CPU then reserves a certain amount of power for these tasks leaving fewer resources to process your recordings. Resulting in crackles, dropouts and glitches in the sound.
Of course not every aforementioned sound problem is caused by DPC. You can experience the same also when you set the buffer size of ASIO driver too low or use too many effects plug-ins or tracks in the project. So be careful and check those first before you blame DPC latency which usually causes sound issues repeating every so often.
DPC latency can affect all computers regardless of how powerful machines they are. Most vulnerable are laptop computers because DPC is mainly related to wireless cards and battery management. And, of course, we are talking mostly about PC platform as Apple guys have – again – much better situation…
But how can you find out for sure that you have DPC problems? Thankfully there is a little program called DPC Latency Checker by SysInternals that you can run without installation. Than just wait for good news in form of green (or occasional yellow) bars or bad ones of red bars.
Surely, the lower and more consistent flow of the bars the better performance of your system. If the graph displays bars going to red area (more than 2000μs) regularly, then your system is highly prone to audio dropouts.
The first step you can take when trying to resolve the DPC latency problem is to update all drivers and also BIOS in your computer.
Secondly, make sure you are not overloading your DAW software and your computer with tons of tracks, virtual instruments and plug-ins. Freeze some of the tracks and try to rise the ASIO buffer to acceptable level (during mastering, mixing or any post-recording processing you don’t need as low buffer settings as during recording).
If this hasn’t resolved your audio dropouts problems, third thing you can try is turning off Windows Aero if you are on Vista or Windows 7, set up Sleep mode to “Never”, turn off screen saver, disconnect from network, disable anti-virus and anti-spyware programs.
If that doesn’t resolve the issue, you can also try disabling hardware devices and checking the result. Run Device Manager (can be found in Control Panel) and try to disable (in right click menu) just one device at the time and check for change in DPC Latency Checker graph. However, don’t turn off all of the devices! Hardware that you should try to switch off are: wireless (WLAN) cards, built-in soundcard (if you are also using external, more professional device), some USB and FireWire devices. If there is no change in latency graph, re-enable the device.
The last solution I heard about is very risky and rather extreme as it suggests disabling Windows’ system driver ACPI.sys. This driver, among other functions, takes care about power management on laptop computers. I haven’t tried to disable it and would recommend to do so just at your own risk as it may take out some other Windows vital functionality. Generally it is easier to disable ACPI.sys on Windows XP machine than on more recent Windows versions.
My last words about this issue would be “better do deep research on the computer before buying it than trying to resolve DPC latency problem after you spent the money“. Check many different resources, like manufacturer’s or other forums. Don’t trust the fancy names like “Studio” as most of these laptops are not suitable for music production (oh dear, I wish I knew about DPC earlier – I own Dell Studio laptop…). And read my website to be aware of similar issues!
Wish you all good nerves and a lot of luck fighting DPC and other latencies! ;)