CTS Verifier Pro Audio Test

Android 10 and higher include a CTS Verifier test for Pro Audio compliance, which tests round-trip audio latency. Unlike many CTS Verifier tests that run automatically, the Pro Audio test requires user intervention to select and connect an appropriate peripheral to the device under test (DUT).

Selecting an audio peripheral

An appropriate peripheral is one that has sufficient playback and record functionality and can directly connect to the DUT to accurately measure round-trip latency through the audio path.

Note: Because analog, digital, and Bluetooth headsets can't be directly connected to device outputs and inputs, these peripherals are not appropriate peripherals and can't used for the Pro Audio test.

Acceptable peripherals include the following:

• USB audio interface. This peripheral can be any USB audio interface that can have its outputs and inputs directly connected to the device with patch cables. All mandated USB audio interfaces required by the USB Audio Peripherals Play or Record CTS Verifier test meet this peripheral requirement. See the figure below for an example.

  

  Figure 1. Example USB audio interface

  When using a USB interface with input level controls, you might need to adjust the controls to a nonzero value; this is typically done when calibrating the signal level (described below). If the audio interface passed the USB Audio Peripheral Record test, the input level setting used in that test should work in the Pro Audio test as well.

• Loopback plug, USB-C digital-to-analog adapter. See the figure below for an example.

  

  Figure 2. Example loopback plug with USB-C digital-to-analog adapter

• Loopback plug, 3.5 mm analog jack. See the figure below for an example.

  

  Figure 3. Example loopback plug with 3.5 mm analog jack

Setting up the test environment

To measure round-trip latency through the audio path, set up a test environment that includes the selected audio peripheral and the DUT with the necessary loopback app installed. When using a USB interface peripheral, calibrate the sound levels to ensure that the Pro Audio tests runs smoothly.

To set up the test environment:

1. Directly connect an appropriate audio peripheral to the DUT.

2. On the device, download and install the Dr. Rick O'Rang loopback app. For app source code, refer to GitHub.

3. Ensure that the loopback app has been granted all requested permissions. (If the app doesn't have all permissions, it will run but won't return test values.)

4. Calibrate the loopback app (optional). You might need to calibrate the sound levels on the loopback app when using a USB interface (calibration isn't typically needed when using a 3.5 mm analog jack). After setting sound levels, the loopback app retains calibrated settings until the next device reboot. To calibrate:

   1. On the device, launch the loopback app and run the function Calibrate Sound Level Now.

   2. On the USB interface, adjust the input levels as needed to get a signal level that can be measured. See the figure below for an example from a PreSonus AudioBox USB.

      

      Figure 4. Example USB interface input levels

Running the Pro Audio test

After you've directly connected the selected audio peripheral to the device and installed the loopback app (with all permissions granted) on the device, you're ready to run the Pro Audio test.

To run the CTS Verifier Pro Audio test:

1. On the device, launch the CTS Verifier app.

2. In the list of tests, select Pro Audio Test.

3. In the Pro Audio Test module, verify that test prerequisites are met (values are true or N/A), then tap Round-Trip Test. See the figure below for an example.

   

   Figure 5. Example CTS Verifier, Pro Audio test module

   The loopback app appears onscreen briefly, then automatically runs the Pro Audio test to determine the round-trip latency. See the figure below for an example.

   

   Figure 6. Example loopback app before starting the Pro Audio test

4. Wait for the loopback app to complete the test. When finished, the app returns a Round Trip Latency measurement and a Confidence value.

5. Use the returned values to verify that all CDD Pro Audio requirements have been met. For latency criteria, see Professional Audio.

6. Tap to indicate compliance.

Troubleshooting

The loopback app runs but doesn't return any values.

Ensure that the loopback app has been granted all requested permissions, then run the test again.

The Confidence value is too low or unknown.

To get a sufficient Confidence value, you might need to run the test more than once.