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

RTL Utility is free for use, however if you would like to contribute towards its development, then you are most welcome to do so!


User guide (PDF)

Version Date Builds Changes
1.0.4 24‑Apr‑2022
  • Added a column for user notes to the log table (double click to edit)
  • Better detection of sample rate changes from device's own control panel (or from Audio & Midi settings on MacOS)
  • Test now fails and aborts if device is reconfigured externally
  • More informative notifications when test signal not detected
  • Improved font rendering on lower resolution monitors
  • Fixed issue with initial sort order of log table
  • Styling tweaks
1.0.3 30‑Dec‑2021
  • Fixed bug causing crashes when trying to select WASAPI (Windows Audio) devices
1.0.2 18‑Nov‑2021
  • Fixed issue where some devices would have incorrect measurements for buffer sizes larger than 2048 samples
  • Fixed issue where the clear log buttons had no effect - sorry about that!
1.0.1 10‑Nov‑2021 Bug fix for MOTU M4 devices enabling them to test at other sample rates
1.0.0 02‑Oct‑2021 New features
  • Completely new & robust detection algorithm which performs optimally for both clean and noisy loopback paths
    • Works nicely for loopback paths with acoustic coupling, e.g. PA system measurements. Note that the RTL will include the delay due to the physical distance between the transducers.
    • If multiple channels are tested at the same time, only the result for the best channel will be recorded.
  • The results table on the Log tab has been updated
    • History from previous runs is now retained
    • You can delete a row by selecting it and pressing the delete key
    • You can sort the table by clicking on a column header
    • Column settings will be persisted between sessions
    • You can click a button to reset to the default layout
    • You will now be asked to confirm if you want to clear the log table
  • Added details of the components of latency for CoreAudio (device latency, safety offset and stream latency)
  • The tooltip for the msec result now shows the equivalent distance for the delta between stored and current measurement (assuming speed of sound = 343 m/s)
  • Added support for sample rates up to 768 kHz and samples sizes of 32768
  • Added an application debug log which includes audio device and RTL measurement debug info (including a chart of the detection output)
  • You can now zoom the GUI (use the buttons in the bottom right, or Ctrl + Mouse Wheel on the background, double-click on background to reset)
  • Previous size of the application window, zoom level and full screen status are restored at launch
  • Improved handling of external buffer size changes so that the app updates correctly (e.g. with RME devices)
  • The audio device manager now refreshes available buffer sizes after the sample rate is changed (e.g. with RME devices)
Other improvements
  • Replaced return loss with return level (e.g. a return loss of 11.0 dB will now be referred to as a return level of -11.0 dB)
  • Added Reported RTL to the most recent results panel (now show this and signal quality metrics even if measurement was invalid)
  • Added warning that measuring RTL using Windows Audio is not recommended (use ASIO instead)
  • Warnings about suspect results are now shown on the most recent results panel instead of showing an alert window
0.5.2 19‑Sep‑2020
  • 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 16‑Apr‑2020
  • 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 30‑Dec‑2018
  • 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 03‑Nov‑2018
  • Fresh build with latest from the JUCE develop branch (including lower sample rate options)
  • OS X build not updated
0.4.9 29‑Jul‑2018
  • Fixed issue where invalid measurements where being logged as valid
  • Added OS X build

Problems opening the download on macOS?

Oblique Audio is not not registered with Apple, so you may get warned against opening the app after download. For information on how to proceed, see here. TLDR; right-click or control-click then choose "Open".

Problems with SmartScreen on Windows?

We have registered RTL Utility with Microsoft but due to the relatively small number of downloads it usually gets flagged as unrecognised. If you get a notice that "Windows protected your PC" you may choose to click the "More info" link, then "Run anyway".

Other 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.