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47 lines
2.0 KiB
47 lines
2.0 KiB
Mega Drone
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==========
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Ever wondered what 100 square waves sound like when played together? Well now you can find out!
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Mega Drone is an app which creates 100 oscillators, combines their output in a mixer and plays the resulting sound.
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This sample demonstrates how to obtain the lowest latency and optimal computational throughput by:
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1) Leaving Oboe to choose the best default stream properties for the current device
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2) Setting performance mode to LowLatency
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3) Setting sharing mode to Exclusive
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4) Setting the buffer size to 2 bursts
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5) Using the `-Ofast` compiler optimization flag, even when building the `Debug` variant
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6) Using [`getExclusiveCores`](https://developer.android.com/reference/android/os/Process#getExclusiveCores()) (API 24+) and thread affinity to bind the audio thread to the best available CPU core(s)
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7) Using a `StabilizedCallback` which aims to spend a fixed percentage of the callback time to avoid CPU frequency scaling ([video explanation](https://www.youtube.com/watch?v=C0BPXZIvG-Q&feature=youtu.be&t=1158))
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This code was presented at [AES Milan](http://www.aes.org/events/144/) and [Droidcon Berlin](https://www.de.droidcon.com/) as part of a talk on Oboe.
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The [following article explaining how to debug CPU performance problems](https://medium.com/@donturner/debugging-audio-glitches-on-android-ed10782f9c64) may also be useful when looking at this code.
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Implementation details
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---
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The stream properties are left to Oboe as such the app must output audio data in a format which matches that of the stream.
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Four different formats are supported:
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|Channel count|Format|
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|-------------|------|
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|1 - Mono|16-bit int|
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|2 - Stereo|16-bit int|
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|1 - Mono|Float|
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|1 - Stereo|Float|
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The signal chain for mono streams is:
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Oscillators->Mixer
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For stereo chains a mono to stereo converter is added to the end of the chain:
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Oscillators->Mixer->MonoToStereo
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The compiler optimization flag `-Ofast` can be found in [CMakeLists.txt](CMakeLists.txt).
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Screenshots
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-----------
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