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Wwise SDK 2025.1.0
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Android audio latency has always been an issue for all applications. Some devices exhibit up to 150 ms of latency, although the usual latency is below 100 ms.
Over the years, Google introduced the several "paths" through which audio can flow from an app to the device's audio hardware:
When supported, these paths bypass various levels of internal processing to reduce the latency between the app and the hardware. Overall latency can be reduced to a few dozen milliseconds. It is important to note that it is not mandatory for the hardware manufacturers to implement these paths; many do not. Furthermore, some devices can report a fast path without it actually being implemented. Therefore, a game cannot rely on the existence of fast audio paths on the end-user's devices. If your game is for a wide target market, you should design your game audio without using this feature.
Generally, a lower latency will incur a higher CPU cost. The processing of RTPC updates, game object positions, and other game inputs is done on a per-frame basis. Therefore, with a smaller frame, this is processed more often. The balance between latency and CPU usage can only be found through experimentation. There is no hard rule.
A few settings will control the latency of audio in the Wwise SDK:
AkPlatformInitSettings::uSampleRate: Sample rate to use. When set to 0 (the default), the hardware preferred rate is selected, allowing use of the fast audio path.AkPlatformInitSettings::uNumRefillsInVoice: Number of buffers to pre-process. This is protection against CPU availability issues or interruption.AkInitSettings::uNumSamplesPerFrame: Number of samples per buffer.AkPlatformInitSettings::eAudioPath: Which audio path to prefer based on device capabilities.The default settings returned by AK::SoundEngine::GetDefaultSettings() and AK::SoundEngine::GetDefaultPlatformInitSettings() are "safe" settings for most devices in most conditions. Using those will set:
uSampleRate to the hardware preferred rate. This is usually 48 kHz or 44.1 kHz.uNumSamplesPerFrame to 512.uNumRefillsInVoice to 4.AkPlatformInitSettings::eAudioPath to AkAudioPath_LowLatency.Advantages: This setup will select an appropriately low-latency audio path on devices that support it. There are also many fewer constraints on the CPU usage of the audio design.
Disadvantages: Four frames of audio are pre-processed to allow some room in CPU variation, which can cause higher latency on devices that may not need the headroom.
To initialize Wwise with the lowest latency, call AK::SoundEngine::GetDefaultSettings() and AK::SoundEngine::GetDefaultPlatformSettings(), then apply the following changes:
AkPlatformInitSettings::uNumRefillsInVoice to 2.AkPlatformInitSettings::eAudioAPI to AkAudioAPI_AAudio.AkPlatformInitSettings::eAudioPath to AkAudioPath_Exclusive.Advantages: Lowest latency possible.
Disadvantages: Available CPU is limited. The time allotted to rendering audio is very short and can be easily disturbed by other events on the system. CPU overhead of audio designs (such as RTPCs, Switches, Positioning, and containers) is a concern and needs to be monitored carefully. Also, device compatibility is reduced. Only devices running Android 8.1 and above will have audio.
When the time required to process an audio frame is lower than what the CPU can handle, audio starvation occurs. At this point, users may hear audible pops and glitches if the game is not outputting silence.
If this glitching is unacceptable, you may opt out of this behavior by making sure to set uNumRefillsInVoice to an initial value large enough to never cause starvation. uNumRefillsInVoice will need to be set to at least 3, usually 4 in most games, to have some headroom for CPU usage variations.
Many Bluetooth devices cannot be low latency or use a fast audio path. In fact, to have glitchless audio with a Bluetooth device, the buffering must be a lot higher. Wwise will detect the usage of a high-latency Bluetooth headset and automatically override AkPlatformInitSettings::uNumRefillsInVoice to reach a latency of 170 ms.
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