What is DPC?
DPC (Deferred Procedure Call) is the operation that Windows uses to assign a priority to processes/drivers that run at the same time in the same system. When certain processes unrelated to streaming audio take longer to process than normal, audio drivers will have difficulty sending and receiving the processed data, often resulting in audio distortion, pops and clicks, and will occasionally cause interfaces or devices to disconnect from your computer altogether.
When troubleshooting DPC Latency, it's important to realize that the primary deciding factor when these issues occur is largely going to center around device drivers. While required for usage, an outdated driver may cause additional strain on your computer's processes, resulting in slower processing time and
Its important to understand that DPC latency is not the only possible cause for the aforementioned audio distortion. To test whether or not this is the cause of this issue, you can use the following software, developed by Respledence : Latency Mon
(Windows 7 and later).
To run the tool, click the Play button while playing audio that is being processed by your interface. After several minutes, if there are no DPC problems, the scan will report such.
If problems do occur, the reporting text will be red and the drivers and processes that are the likely cause of the problem will be displayed.
Solving DPC Latency issues
Occasionally, device drivers can be updated through Windows Updates in addition to the manufacturer's release. Its important to ensure to check that these drivers are up to date as soon as you start experiencing DPC issues or any sort of audio distortion. To do this, you can follow the Windows OS specific instructions outlined below.:
- Windows 7: Go to Start > Programs > Windows Update > click 'Check for updates'
- Windows 8: Go to Control Panel > Windows Update > click 'Check for updates'
- Windows 10: Click the Windows icon in the bottom left corner of the screen > Settings > Updates and Security
Intel based systems use the Driver Update Support Assistant to find driver updates for your system. This tool can be downloaded here.
If updating these Windows drivers does not rectify your DPC issues, you must then isolate the driver or processes that are causing these issues to occur. Common problematic areas are:
- Network/WiFi adapters
- Card readers
- Unused Audio Devices
- Bluetooth adapters
- Graphics card
To narrow down which device causing the issue you can try disabling the above components in Control Panel > Device Manager (Note : on-board graphics cards should not be disabled as part of this troubleshooting) and then run the LatencyMon software. If no errors appear, it is safe to assume that the device you've disabled is the device causing these issues, and you should be able to continue with your work without further issues caused by DPC Latency.