DPC (Deferred Procedure Call) latency is the leading cause of audio crackles, pops, and recording glitches in Windows. It can also contribute to micro-stuttering in games. LatencyMon from Resplendence Software is the go-to diagnostic tool for identifying which drivers are causing high latency spikes.

What is DPC Latency?

When hardware needs CPU attention, it generates an interrupt. The CPU defers non-critical work to DPCs — small routines that run at very high priority. Poorly written drivers can hold the CPU in a DPC too long, blocking the audio engine from refilling its buffer. The result: clicks, pops, or dropouts in audio.

Target DPC latency for clean real-time audio: under 300 microseconds. Under 150µs is excellent.

Download and Run LatencyMon

Download from resplendence.com/latencymon (free)
Run as Administrator
Click the Play button to start monitoring
Browse the web, play audio, use your PC normally for 5–10 minutes
Watch the Highest DPC routine execution time graph

A green bar throughout = your system is fine. Yellow/red spikes = problem drivers.

Reading the Results

Switch to the Drivers tab for the most important view:

Highest execution (µs): worst-case DPC time — this column matters most
Total execution (µs): aggregate time across all runs
Count: how many DPCs this driver triggered

Look for any driver with a Highest execution value over 1000µs (1ms). Common culprits:

Driver	Culprit
`ndis.sys`	Network adapter (WiFi especially)
`nvlddmkm.sys`	NVIDIA GPU driver
`ataport.sys`	Storage controller / HDD
`usbxhci.sys`	USB 3.0 controller
`dxgkrnl.sys`	DirectX kernel — often GPU related
`intelppm.sys`	Intel CPU power management
`storport.sys`	Storage port driver
`acpi.sys`	ACPI / power management

Fixing Common DPC Latency Causes

WiFi adapter (ndis.sys)

WiFi drivers are the #1 cause of DPC latency:

Device Manager → Network Adapters → right-click WiFi → Properties → Advanced tab
Disable: Interrupt Moderation, U-APSD (if present), Power Save Mode (set to Maximum Performance)
Or switch to Ethernet — wired connections rarely cause DPC issues

# Disable WiFi adapter power management
Get-NetAdapter | Where {$_.Name -like "*Wi-Fi*"} | Set-NetAdapterPowerManagement -AllowComputerToTurnOffDevice Disabled

NVIDIA GPU driver (nvlddmkm.sys)

NVIDIA drivers are a common culprit:

Use DDU (Display Driver Uninstaller) to fully remove, then reinstall the latest Studio or Game Ready driver
In NVIDIA Control Panel → Power Management Mode → Prefer Maximum Performance
Disable NVIDIA High Definition Audio driver if not using HDMI audio

USB controller (usbxhci.sys)

Disconnect USB devices one at a time and re-run LatencyMon to identify the problem device. USB DACs, audio interfaces, and some hubs cause DPC spikes.

Disable USB selective suspend:

Control Panel → Power Options → Change plan settings → Change advanced power settings
USB settings → USB selective suspend setting → Disabled

Storage (ataport.sys, storport.sys)

Update storage controller drivers (Intel RST or AMD SATA drivers)
Disable HDD power management in Device Manager → Disk Drives → Properties → Policies

Intel CPU power management (intelppm.sys)

On Intel systems, aggressive P-state transitions can spike DPC:

Set Windows power plan to High Performance or Ultimate Performance
In Intel’s Extreme Tuning Utility: disable Speed Shift or set EPP to 0 for minimum latency

BIOS Settings for Lower Latency

Several BIOS options reduce DPC latency:

C-States: disable C6, C7, C8 sub-states (or all C-states for maximum latency reduction)
HPET (High Precision Event Timer): controversial — test with and without
CPU Power Management: disable in BIOS for real-time audio work
USB Legacy Support: disable if not needed

# Enable/disable HPET in Windows
bcdedit /set useplatformclock true   # enable HPET
bcdedit /set useplatformclock false  # disable HPET (default in Win 11)

Test both and use LatencyMon to see which is better on your hardware.

Audio Buffer Size

Even with perfect DPC latency, too-small audio buffers cause dropouts:

In your DAW or audio interface software, increase the buffer size to 128 or 256 samples
Only reduce buffer size as low as your system can handle for real-time recording
For playback-only, 512–1024 samples is fine

LatencyMon Report

At any time, save a detailed HTML report:

File → Save HTML Report

This captures all driver statistics, hardware info, and system info — useful for posting in support forums.

For most users, disabling WiFi adapter power management and updating GPU drivers eliminates 90% of DPC latency problems. Ethernet + a clean driver installation is the fastest path to a latency-clean system.