Using LatencyMon to collect DPC Latency Data

Deferred Procedure Call (DPC) latency is the time your PC waits for a hardware device to complete a request for service (data) from the operating system.  If these latencies are very long in duration, on the order of 1500 microseconds (uS)  and greater, it can adversely effect your PC's ability to run a real-time audio application like PowerSDR or SmartSDR DAX, resulting in stuttering audio, corrupted audio buffers, distorted audio.

Long duration DPCs are *always* caused by poorly written device drivers (software).  This can be the driver itself or the PC's BIOS.  Upgrading the device driver to a more current version provided by the hardware manufacturer (and not Microsoft via Microsoft Update) and/or a BIOS update can mitigate the long duration DPC latency issues, but first you need to identify the offending driver.

For Windows Vista, Win7 and Win8, you can use a free application called LatencyMon to detect problems with your PC's ability to run a real-time audio application.  This information can be used to identify problem areas.

The following procedure will instruct you how to download, install, run and capture the LatencyMon data that can be used for problem troubleshooting.

  1. Download LatencyMon ( and install it.
  2. Run LatencyMon after installing it.
  3. Click on the Green side-ways triangle to start tracing. Start your FlexRadio SDR application and the digital mode program so that the audio anomalies are observed. Let LatencyMon run for several minutes or until the audio probles are observed.
  4. Then click on the Red square to stop tracing. Click on Edit and select "copy Report Text to Clipboard".
  5. Then copy the report to a text file or your HelpDesk ticket so that a Technical Support Engineer can evaluate the results.
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