Effective in 2026, to align with our trunk stable development model and ensure platform stability for the ecosystem, we will publish source code to AOSP in Q2 and Q4. For building and contributing to AOSP, we recommend utilizing android-latest-release instead of aosp-main. The android-latest-release manifest branch will always reference the most recent release pushed to AOSP. For more information, see Changes to AOSP.
Audio loopback dongle
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The diagram and photo below show an audio loopback
dongle
for the
headset connector.
The Chrome hardware team designed this circuit and plug for functional testing;
however it has many other uses too. The Android audio team uses it to measure
round-trip audio latency,
by sending an encoded signal through the output and then looking for that matching signal on the input.
The time between the two is the combined input plus output latency.
This technique is used in OboeTester and in CTS Verifier.
A Loopback Dongle based on the circuit below is available from
PassMark Software.
This isn't a recommendation or an endorsement. Google does not have a business relationship with PassMark.
Circuit
Figure 1. circuit diagram
To ensure that the output signal will not overload the microphone input,
we cut it down by about 20dB.
The resistor loads tell the microphone polarity switch that
the audio loopback dongle is a US/CTIA pinout Tip Ring Ring Shield (TRRS) plug.
Assembled
Figure 2. Assembled
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
Last updated 2025-02-27 UTC.
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