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| <title>Audio Latency Measurements</title> |
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| |
| <p><a href="http://en.wikipedia.org/wiki/Latency_%28engineering%29">Latency</a> |
| is an important system performance metric. While many kinds of |
| <a href="latency.html">audio latency</a> metrics exist, one useful and |
| well-understood metric is |
| <a href="latency_measure.html#measuringRoundTrip">round-trip latency</a>, |
| defined as the time it takes for an audio signal to enter the input of a mobile |
| device, be processed by an app running on the application processor, and exit |
| the output.</p> |
| |
| <img src="images/round_trip_on_device.png" alt="Round-trip audio latency on |
| device" id="figure1" /> |
| <p class="img-caption"><strong>Figure 1.</strong> Round-trip audio latency on |
| device: T<sub>output</sub> - T<sub>input</sub></p> |
| |
| <p>This page provides round-trip audio latency measurements for select |
| Nexus/Pixel devices and Android platform versions.</p> |
| |
| <h2 id="why">Why we measure latency</h2> |
| |
| <p>Google measures and reports latency so Android application developers have |
| the data they need to make informed decisions about available latency on actual |
| devices. By sharing latency numbers for select Nexus and Pixel devices, we hope |
| to encourage the entire Android community to measure, publish, and reduce |
| latency on <em>all</em> Android devices. Please join us in our commitment to |
| reducing audio latency!</p> |
| |
| <h2 id="app">Application impact on latency</h2> |
| |
| <p>Signal processing can add the following types of delay to latency:</p> |
| <ul> |
| <li><strong>Algorithmic</strong>. This delay is inherent and does not vary with |
| the CPU. An example is the delay added by a |
| <a href="http://en.wikipedia.org/wiki/Finite_impulse_response">finite impulse |
| response</a> (FIR) filter.</li> |
| <li><strong>Computational</strong>. This delay is related to the number of |
| required CPU cycles. For example, attenuation of a signal is usually done by a |
| multiplication operation that takes a varying number of cycles depending on the |
| CPU.</li> |
| </ul> |
| |
| <h2 id="how">How we measure</h2> |
| |
| <p>We made the measurements listed on this page using the |
| <a href="loopback.html">Dr. Rick O'Rang audio loopback dongle</a> and an |
| <a href="latency_measure.html#larsenTest">audio feedback (Larsen effect) |
| test</a>. Measurements assume the application signal processing adds zero |
| algorithmic delay and near-zero computational delay.</p> |
| |
| <p>We measure round-trip latency via the headset connector for several reasons: |
| </p> |
| <img src="images/round_trip_via_headset_connector.png" alt="Round-trip latency |
| via headset connector" id="figure2" /> |
| <p class="img-caption"><strong>Figure 2.</strong> Round-trip latency via headset |
| connector: T<sub>output</sub> - T<sub>input</sub></p> |
| <ul> |
| <li>Important music applications (such as guitar and voice processing) use the |
| headset connector.</li> |
| <li>Measuring round-trip latency of the on-device microphone and speaker can be |
| cumbersome, as it is difficult to keep a feedback loop in open air from entering |
| uncontrolled oscillation.</li> |
| <li>On-device transducers are small and sacrifice frequency response to achieve |
| their small size. To compensate, digital signal processing is applied but |
| increases algorithmic delay for the on-device path.</li> |
| </ul> |
| |
| <p>There are cases where on-device microphone and speaker latencies <em>do</em> |
| matter, but they are usually for one direction, not round-trip. Techniques for |
| measuring unidirectional latency are described at |
| <a href="latency_measure.html#measuringOutput">Measuring Output Latency</a> |
| and |
| <a href="latency_measure.html#measuringInput">Measuring Input Latency</a>.</p> |
| |
| <h2 id="examples">Example measurements</h2> |
| |
| <p>The measurements listed below are specific to a |
| <a href="/setup/build-numbers.html">build number</a>. Devices are listed in |
| approximate order of initial release and by platform version; you can also |
| <a href="#chart">view latencies in a chart</a>. The test application uses the |
| Android native audio API based on OpenSL ES.</p> |
| |
| <table> |
| <tr> |
| <th>Model</th> |
| <th>Platform<br />version</th> |
| <th>Build<br />number</th> |
| <th>Sample rate<br />(Hz)</th> |
| <th>Buffer size<br />(frames)</th> |
| <th>Buffer size<br />(ms)</th> |
| <th>Round-trip<br />latency (ms)<br />± one buffer</th> |
| </tr> |
| |
| <tr> |
| <td>Nexus One</td> |
| <td>2.3.6</td> |
| <td>GRK39F</td> |
| <td>44100</td> |
| <td>768</td> |
| <td>17.4</td> |
| <td>345</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus S</td> |
| <td>2.3.6</td> |
| <td>GRK39F</td> |
| <td>44100</td> |
| <td>1024</td> |
| <td>23.2</td> |
| <td>260</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus S</td> |
| <td>4.0.4</td> |
| <td>IMM76D</td> |
| <td>44100</td> |
| <td>1024</td> |
| <td>23.2</td> |
| <td>260</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus S</td> |
| <td>4.1.2</td> |
| <td>JZO54K</td> |
| <td>44100</td> |
| <td>880</td> |
| <td>20</td> |
| <td>210</td> |
| </tr> |
| |
| <tr> |
| <td>Galaxy Nexus</td> |
| <td>4.0.1</td> |
| <td>ITL41D</td> |
| <td>44100</td> |
| <td>976</td> |
| <td>22.1</td> |
| <td>270</td> |
| </tr> |
| |
| <tr> |
| <td>Galaxy Nexus</td> |
| <td>4.3</td> |
| <td>JWR66Y</td> |
| <td>44100</td> |
| <td>144</td> |
| <td>3.3</td> |
| <td>130</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 4</td> |
| <td>4.2.2</td> |
| <td>JDQ39E</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>195</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 4</td> |
| <td>5.1</td> |
| <td>LMY47O</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>58</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 10</td> |
| <td>5.0.2</td> |
| <td>LRX22G</td> |
| <td>44100</td> |
| <td>256</td> |
| <td>5.8</td> |
| <td>36</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 10</td> |
| <td>5.1</td> |
| <td>LMY47D</td> |
| <td>44100</td> |
| <td>256</td> |
| <td>5.8</td> |
| <td>35</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 7<br />2013</td> |
| <td>4.3</td> |
| <td>JSR78D</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>149</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 7<br />2013</td> |
| <td>4.4</td> |
| <td>KRT16S</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>85</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 7<br />2013</td> |
| <td>5.0.2</td> |
| <td>LRX22G</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>64</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 7<br />2013</td> |
| <td>5.1</td> |
| <td>LMY47O</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>55</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 7<br />2013</td> |
| <td>6.0</td> |
| <td>MRA58K</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>55</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5</td> |
| <td>4.4.4</td> |
| <td>KTU84P</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>95</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5</td> |
| <td>5.0.0</td> |
| <td>LRX21O</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>47</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5</td> |
| <td>5.1</td> |
| <td>LMY47I</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>42</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5</td> |
| <td>6.0</td> |
| <td>MRA58K</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>38</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 9</td> |
| <td>5.0.0</td> |
| <td>LRX21L</td> |
| <td>48000</td> |
| <td>256</td> |
| <td>5.3</td> |
| <td>35</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 9</td> |
| <td>5.0.1</td> |
| <td>LRX22C</td> |
| <td>48000</td> |
| <td>256</td> |
| <td>5.3</td> |
| <td>38</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 9</td> |
| <td>5.1.1</td> |
| <td>LMY47X</td> |
| <td>48000</td> |
| <td>256</td> |
| <td>5.3</td> |
| <td>32</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 9</td> |
| <td>6.0</td> |
| <td>MRA58K</td> |
| <td>48000</td> |
| <td>128</td> |
| <td>2.6</td> |
| <td>15</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 6</td> |
| <td>5.0.1</td> |
| <td>LRX22C</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>65</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 6</td> |
| <td>5.1</td> |
| <td>LMY47I</td> |
| <td>48000</td> |
| <td>240</td> |
| <td>5</td> |
| <td>42</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 6</td> |
| <td>6.0</td> |
| <td>MRA58K</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>33</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5X</td> |
| <td>6.0</td> |
| <td>MDA89E</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5X</td> |
| <td>8.0.0</td> |
| <td>OPR4.170623.020</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 5X</td> |
| <td>8.1.0</td> |
| <td>OPM2.171019.029.C1</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 6P</td> |
| <td>6.0</td> |
| <td>MDA89D</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 6P</td> |
| <td>8.0.0</td> |
| <td>OPR5.170623.014</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Nexus 6P</td> |
| <td>8.1.0</td> |
| <td>OPM5.171019.019</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Pixel</td> |
| <td>7.1.2</td> |
| <td>NHG47L</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Pixel</td> |
| <td>8.0.0</td> |
| <td>OPR3.170623.013</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Pixel</td> |
| <td>8.1.0</td> |
| <td>OPM1.171019.021</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Pixel XL</td> |
| <td>7.1.2</td> |
| <td>NHG47L</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| <tr> |
| <td>Pixel XL</td> |
| <td>8.0.0</td> |
| <td>OPR3.170623.013</td> |
| <td>48000</td> |
| <td>192</td> |
| <td>4</td> |
| <td>18</td> |
| </tr> |
| |
| </table> |
| |
| <a id=chart></a> |
| <img src="/devices/audio/images/round-trip-latencies.png" /> |
| <p class="img-caption"><strong>Figure 3.</strong> Round trip latencies.</p> |
| |
| </body> |
| </html> |
