RTL Utility

RTL Utility is a tool for measuring the Round Trip Latency of your Digital Audio Workstation (DAW) and audio interface. The utility is used for low latency performance testing by system builders, reviewers, device manufacturers and at dawbench.com.

When your DAW sends data to your audio interface for playback, it doesn’t send a continuous stream of data one bit at a time. What it does is fill up a section of RAM called a buffer and sends that in a single message when it is ready. Before sending the next message it has to fill the buffer again. This wait time introduces a latency, or delay, between something happening in your DAW and when you actually hear it.

While you are recording, the audio interface buffers and sends data to your DAW in a similar fashion. This introduces latency into your recordings.

If you send a signal from your DAW, out through the audio interface and back in via a loopback patch, then there will be a round trip latency which is the sum of the output and input delays. This is the RTL.

You'll need a physical loopback patch to measure RTL



User guide (PDF)


Version Date Builds Changes
0.5.2 19th September 2020 Windows 64-bit
Windows 32-bit
OS X
  • Reinstated manual tweaks to latency reported by driver for CoreAudio (fixes reported latency on macOS)
  • Just for Vin - show RTL (msec) to 3 decimal places
  • Fixed issues with https so version check works on macOS
0.5.1 16th April 2020 Windows 64-bit
Windows 32-bit
OS X
  • Improved latency measurement algorithm for acoustically coupled measurements
  • Removed manual tweaks to latency reported by driver (doesn't affect measurement)
  • Added feature to store measurement (comparisons shown in tooltips)
  • Added warning if driver reports buffer underrun or overrun
  • Updated and re-ordered columns in table and log file
0.4.11 30th December 2018 Windows 64-bit
Windows 32-bit
OS X
  • Increased robustness of the latency measurement algorithm
  • Slightly improved audio device compatibility (more tolerant of larger buffer sizes and higher channel counts)
  • Corrected return loss measurements
  • Minor GUI tweaks & fixes
0.4.10 3rd November 2018
  • Fresh build with latest from the JUCE develop branch (including lower sample rate options)
  • OS X build not updated
0.4.9 29th July 2018
  • Fixed issue where invalid measurements where being logged as valid
  • Added OS X build



Problems running on Windows?

In order to run RTL Utility, you need to have Microsoft Visual C++ Redistributable for Visual Studio 2015, 2017 and 2019 installed. As this package is needed by lots of different applications, you probably already have it on your system. If not, you will get one of the following errors:

If you see any of these errors then please install the latest redistributable from here.