Overview

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. If processes that aren't involved in streaming audio take up processing time for longer than they really should then this can prevent audio drivers from being able to send/receive data in an appropriate amount of time, leading to audible issues (e.g. pops/clicks, dropouts, 'glitchy' audio and sometimes even device disconnections).

A common cause for DPC latency is out of date device drivers and Windows processes that are not optimised correctly. Many processes/drivers are involved in streaming audio, and many other processes/drivers can cause interruptions in the audio stream.

Analysis

To analyse whether DPC latency could be the cause for any pops, clicks, or disconnections you might be experiencing, you can run the following software tool: Latency Mon (Windows 7 and later).

To run the tool, click the Play button and then play audio from any application through your audio interface for a couple of minutes. If there are no DPC problems, the scan will report this:

If there are problems, the reporting text will be black/red and the drivers/processes that are the likely cause of the problem will be displayed:

Solving DPC Latency issues

Updates for some processes/drivers are often delivered via Windows Update. It's recommended that you ensure that your version of Windows is fully up-to-date should you encounter any DPC problems, you can update Windows by following these steps:

• 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 10/11: Click the Windows icon in the bottom left corner of the screen > Settings > Updates and Security

If you use an Intel-based system, you can use the Driver Update Support Assistant to find driver updates for your system. This tool can be downloaded here.

If the DPC problems persist after installing all Windows updates, then the next step is to try to deduce the device that's causing the problem. Common problematic areas are:

• Network/Wi-Fi adapters
• Card readers
• Other sound devices that aren't in use
• Bluetooth adapters
• Graphics card

To narrow down which device causing the issue, you can try disabling the above components in Control Panel > Device Manager (only disable your graphics card if you have on-board graphics as well) and then run the DPC test again. If this fixes the problem then this would be a strong indicator that this particular device is the cause of the issue - you can then either leave this disabled when working with audio or check for any updates from the component manufacturer.

Storport.sys issues may be resolved by running the System File Checker as described here.