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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.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-02-27 UTC."],[],[],null,["# Audio loopback dongle\n\nThe diagram and photo below show an audio loopback\n[dongle](http://en.wikipedia.org/wiki/Dongle)\nfor the\n[headset connector](http://en.wikipedia.org/wiki/Phone_connector_(audio)).\nThe Chrome hardware team designed this circuit and plug for functional testing;\nhowever it has many other uses too. The Android audio team uses it to measure\n[round-trip audio latency](/docs/core/audio/latency/measure#measuringRoundTrip),\nby sending an encoded signal through the output and then looking for that matching signal on the input.\nThe time between the two is the combined input plus output latency.\nThis technique is used in [OboeTester](https://github.com/google/oboe/tree/main/apps/OboeTester/docs) and in CTS Verifier.\n\nA Loopback Dongle based on the circuit below is available from\n[PassMark Software](https://www.passmark.com/products/audio-loopback-plug/index.php).\nThis isn't a recommendation or an endorsement. Google does not have a business relationship with PassMark.\n\nCircuit\n-------\n\n\n**Figure 1.** circuit diagram\n\n\nTo ensure that the output signal will not overload the microphone input,\nwe cut it down by about 20dB.\nThe resistor loads tell the microphone polarity switch that\nthe audio loopback dongle is a US/CTIA pinout Tip Ring Ring Shield (TRRS) plug.\n\nAssembled\n---------\n\n\n**Figure 2.** Assembled"]]
