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diff --git a/en/devices/audio/latency_measurements.html b/en/devices/audio/latency_measurements.html index 66a97925..d8483c0c 100644 --- a/en/devices/audio/latency_measurements.html +++ b/en/devices/audio/latency_measurements.html @@ -22,112 +22,85 @@ --> - -<p> -This article gives round-trip audio latency measurements for select devices and -platform versions. -</p> - -<h2 id="definition">Definition</h2> - -<p> -<a href="http://en.wikipedia.org/wiki/Latency_%28engineering%29">Latency</a> -is an important system performance metric. There are many kinds -of <a href="latency.html">audio latency</a> -metrics. One useful and well-understood metric is -<a href="latency_measure.html#measuringRoundTrip">round-trip latency</a>. -Round-trip latency is 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><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> -We measure and report latency so Android -app developers will have the data they need to make informed decisions about available -latency on actual devices. By sharing these numbers for select Nexus devices, we also hope to -encourage the entire Android community to measure, publish, and reduce -latency on <i>all</i> devices. -Please join us in our commitment to reducing audio latency. -</p> +<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> -There are two kinds of delays that a signal processing stage can add to latency: -algorithmic delay and computational delay. -Algorithmic 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. -Computational delay is related to the number of CPU cycles required. -For example, attenuation of a signal is usually done by a multiplication operation, -and this multiplication will take a varying number of cycles depending on the CPU. -</p> +<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> -The measurements below were taken with 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>. -</p> - -<p> -For our measurements, we assume the application signal processing -adds zero algorithmic delay and near zero computational delay. -</p> +<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>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> - There are important music applications, such as guitar and voice processing, - that 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> - The 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> +<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 -<i>do</i> -matter, but they are usually for one direction, not round-trip. -Techniques for measuring unidirectional latency are described at +<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> - -<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> +<a href="latency_measure.html#measuringInput">Measuring Input Latency</a>.</p> <h2 id="measurements">Example measurements</h2> -<p> -The measurements shown are specific to a -<a href="/source/build-numbers.html">build number</a>. -Devices are listed in approximate order of initial release and within device by platform version. -The test application uses the Android native audio API based on OpenSL ES. -</p> +<p>The measurements listed below are specific to a +<a href="/source/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> @@ -420,14 +393,31 @@ The test application uses the Android native audio API based on OpenSL ES. <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 XL</td> + <td>7.1.2</td> + <td>NHG47L</td> + <td>48000</td> + <td>192</td> + <td>4</td> + <td>18</td> +</tr> + </table> -<p></p> -<p></p> +<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> - <p></p> - <img src="/devices/audio/images/round-trip-latencies.png" /> - <p class="img-caption"> -<strong>Figure 3.</strong> Round trip latencies.</p> - </body> +</body> </html> |