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Audio Latency Measurements

In this document

This article gives round-trip audio latency measurements for select devices and platform versions.

Definition

Latency is an important system performance metric. There are many kinds of audio latency metrics. One useful and well-understood metric is round-trip latency. 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.

Round-trip audio latency on device

Figure 1. Round-trip audio latency on device: Toutput - Tinput

Why we measure latency

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 all devices. Please join us in our commitment to reducing audio latency.

Application impact on latency

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 finite impulse response (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.

How we measure

The measurements below were taken with the Dr. Rick O'Rang audio loopback dongle and an audio feedback (Larsen effect) test.

For our measurements, we assume the application signal processing adds zero algorithmic delay and near zero computational delay.

We measure round-trip latency via the headset connector for several reasons:

  • There are important music applications, such as guitar and voice processing, that use the headset connector.
  • 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.
  • 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.

There are cases where on-device microphone and speaker latencies do matter, but they are usually for one direction, not round-trip. Techniques for measuring unidirectional latency are described at Measuring Output Latency and Measuring Input Latency.

Round-trip latency via headset connector

Figure 2. Round-trip latency via headset connector: Toutput - Tinput

Example measurements

The measurements shown are specific to a build number. 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.

Model Platform
version
Build
number
Sample rate
(Hz)
Buffer size
(frames)
Buffer size
(ms)
Round-trip
latency (ms)
± one buffer
Nexus One 2.3.6 GRK39F 44100 768 17.4 345
Nexus S 2.3.6 GRK39F 44100 1024 23.2 260
Nexus S 4.0.4 IMM76D 44100 1024 23.2 260
Nexus S 4.1.2 JZO54K 44100 880 20 210
Galaxy Nexus 4.0.1 ITL41D 44100 976 22.1 270
Galaxy Nexus 4.3 JWR66Y 44100 144 3.3 130
Nexus 4 4.2.2 JDQ39E 48000 240 5 195
Nexus 4 5.1 LMY47O 48000 240 5 58
Nexus 10 5.0.2 LRX22G 44100 256 5.8 36
Nexus 10 5.1 LMY47D 44100 256 5.8 35
Nexus 7
2013
4.3 JSR78D 48000 240 5 149
Nexus 7
2013
4.4 KRT16S 48000 240 5 85
Nexus 7
2013
5.0.2 LRX22G 48000 240 5 64
Nexus 7
2013
5.1 LMY47O 48000 240 5 55
Nexus 7
2013
6.0 MRA58K 48000 240 5 55
Nexus 5 4.4.4 KTU84P 48000 240 5 95
Nexus 5 5.0.0 LRX21O 48000 240 5 47
Nexus 5 5.1 LMY47I 48000 240 5 42
Nexus 5 6.0 MRA58K 48000 192 4 38
Nexus 9 5.0.0 LRX21L 48000 256 5.3 35
Nexus 9 5.0.1 LRX22C 48000 256 5.3 38
Nexus 9 5.1.1 LMY47X 48000 256 5.3 32
Nexus 9 6.0 MRA58K 48000 128 2.6 15
Nexus 6 5.0.1 LRX22C 48000 240 5 65
Nexus 6 5.1 LMY47I 48000 240 5 42
Nexus 6 6.0 MRA58K 48000 192 4 33
Nexus 5X 6.0 MDA89E 48000 192 4 18
Nexus 6P 6.0 MDA89D 48000 192 4 18

Figure 3. Round trip latencies.