High ISR (Interrupted Service Routines) and DPC (Deferred Procedure Calls) latencies prevent your CPU from processing real-time digital audio efficiently (or at all, sometimes). LatencyMon from Resplendence is a free utility that checks your computer's ability to handle digital audio by measuring ISR and DPC execution times as well as hard page faults. It identifies the kernel modules and processes causing high latencies that lead to audio drop outs. LatencyMon also serves well as a simple ISR, DPC, or hard page fault monitor.
LatencyMon's plain but efficient interface has five tabs: Main, Stats, Processes, Drivers, and CPU. We clicked the Start button, and almost immediately LatencyMon delivered the (bad) news in a summary report bolstered by bar graphs: our dual-core Pentium 4-based system didn't have the chops to process raw digital audio and we were likely to experience the drop outs, clicks and pops typical of buffer under-runs. Digital clicks and pops make vinyl surface noise seem pleasant, so we considered ourselves warned. The test runs continuously until you stop it, so we clicked the Stop button, which enabled a Stats tab report summary we could save, copy, or print. The report offered specific recommendations for improving our system's ability to process audio, such as disabling our WLAN, updating the BIOS, and disabling CPU throttling controls. Under Processes, LatencyMon displayed all our system's running processes by file name, PID hard page faults, and other headings. The Drivers and CPU tabs offered similarly detailed reports. The program offers some useful options, such as the ability to select which logical cores to monitor, a tool to set ETW file size, and the ability to measure SMIs and CPU stalls and perform a CPU speed sanity check.
We ran LatencyMon on several PCs, with predictable results: newer, more-powerful machines with multicore CPUs fared best. We found that running LatencyMon after every tweak helped diagnose latency issues and verify the fixes. Whether you're setting up a studio or just want to know how your PC handles buffer-critical data like digital audio, LatencyMon's scans not only provide the data but also the answers.