CTS Verifier Pro Audio Test

This document describes the Android 10 CTS Verifier test for Pro Audio compliance. While most test activities automatically occur when the test begins, testing round-trip latency requires human intervention to connect an appropriate peripheral to the device under test.

Installing the external loopback application

The CTS Verifier Pro Audio Test uses the Dr. Rick O'Rang loopback application to measure round-trip latency through the audio path. This application should be installed using the Play Store link. The source code is available on GitHub.

Assembling required peripherals

To measure round-trip latency through the audio path, you must directly connect an appropriate audio peripheral with playback and record functionality to the device under test.

An acceptable peripheral can be any one of the following:

Description Photo
USB audio interface
  • Can be any USB audio interface that can have its outputs and inputs directly connected to the device with a patch cable(s).
  • Any of the mandated USB audio interfaces required by the USB Audio Peripherals Play or Record CTS Verifier Test meet this peripheral requirement.
CTS Pro Audio
Figure 1. CTS verifier icon
Loopback plug with:
  • USB-C digital to analog adapter

  • 3.5mm analog jack
CTS Pro Audio
Figure 2. Loopback plug with USB-C digital-to-analog adapter
CTS Pro Audio
Figure 3. Loopback plug with 3.5mm analog jack

Calibrating the Loopback app

Before running the Pro Audio test, you must calibrate the sound levels on the Loopback app. To perform calibration:

  1. Ensure the USB interface peripheral is directly connected to the device under test.
  2. Launch the Loopback app on the device.
  3. Run the function Calibrate Sound Level Now.
  4. Adjust the input levels on the USB interface as needed to get a signal level that can be measured. See Figure 4 for example.

    CTS Pro Audio
    Figure 4. USB interface input levels (Presonus AudioBox USB shown)

After calibration is complete, you are ready to run the Pro Audio test. The Loopback app will retain its calibrated settings until the next device reboot.

Running the Pro Audio test

To run the CTS Verifier Pro Audio test:

  1. Open the CTS Verifier application on the device.
  2. Select the Pro Audio Test in the list of tests.
  3. Verify test prerequisites are met (i.e. values are true or N/A) on the Pro Audio Test module.
  4. Tap Round-Trip Test to start the Loopback App (which briefly appears onscreen before automatically running the Pro Audio test).
    CTS Pro Audio
    Figure 5. Pro Audio test module
    CTS Pro Audio
    Figure 6. Loopback app
  5. Wait for the Loopback app to determine the round-trip latency. When the test completes, the app returns the Round Trip Latency measurement and a Confidence value.
    • To get a sufficient Confidence value, you might need to run the test more than once.
    • When using a USB Interface with input level controls, you need to adjust the controls to a non-zero value. This is typically done when calibrating the signal level.
    • Verify all CDD Pro Audio requirements have been met. For details on latency criteria, refer to the Professional Audio section in the Android CDD.
    • Tap CTS Pro Audio to indicate compliance.