Docs: Fixing updates from the Audio team, renaming funplug to
loopback
Bug: 19283199
Change-Id: Ib58f6805472bd453c93fa3668efda546ac0588d5
diff --git a/src/devices/audio/loopback.jd b/src/devices/audio/loopback.jd
new file mode 100644
index 0000000..933972f
--- /dev/null
+++ b/src/devices/audio/loopback.jd
@@ -0,0 +1,58 @@
+page.title=Audio Loopback Dongle
+@jd:body
+
+<!--
+ Copyright 2014 The Android Open Source Project
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+<div id="qv-wrapper">
+ <div id="qv">
+ <h2>In this document</h2>
+ <ol id="auto-toc">
+ </ol>
+ </div>
+</div>
+
+<p>
+The diagram and photo below show an audio loopback
+<a href="http://en.wikipedia.org/wiki/Dongle">dongle</a>
+for the
+<a href="http://en.wikipedia.org/wiki/Phone_connector_(audio)">headset connector</a>
+that we call the "Dr. Rick O'Rang audio loopback dongle."
+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
+<a href="latency_measure.html#measuringRoundTrip">round-trip audio latency</a>,
+via the Larsen effect (feedback loop).
+</p>
+
+<h2 id="loopbackCircuit">Circuit</h2>
+
+<img src="images/loopback_circuit.png" alt="circuit" id="figure1" />
+<p class="img-caption">
+ <strong>Figure 1.</strong> circuit diagram
+</p>
+
+<p>
+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.
+</p>
+
+<h2 id="loopbackAssembled">Assembled</h2>
+
+<img src="images/loopback_assembled.jpg" alt="fully assembled" id="figure2" />
+<p class="img-caption">
+ <strong>Figure 2.</strong> Assembled
+</p>