Hybrid Android / JUCE Audio Library Targeting Music Applications
Maqam
Mobile App Quick Audio & MIDI
Maqam is a graph-based audio processing library for the Android platform. It leverages JUCE for DSP development while leaving the choice of UI frameworks up to the programmer.
It is developed by TAQS.IM and distributed under a friendly MIT license.
Features
- Prebuilt nodes: SFZ player, reverb, delay, low pass filter
- Support for custom nodes
- Compose friendly
- Automatic state persistence
Architecture
The Kotlin AudioGraph and AudioNode classes are backed by juce::AudioGraph
and juce::AudioProcessor respectively. JUCE is only used for DSP,
by design JUCE is used as little as possible. All I/O is managed by Maqam through
the standard Oboe and AMidi
Android libraries and bridged to a JUCE AudioGraph instance, which in turns
manages the individual AudioProcessor instances. This way JUCE does not impose
any kind of restriction over the native Android app, it is just a part of it.
The library deliberately does not an attempt to map JUCE interfaces one to one. It uses JUCE to implement some aspects of iOS' AVAudioEngine while not reinventing the wheel.
Since Android lacks an official audio plugin architecture like AudioUnit on iOS, Maqam's primary use case are standalone applications that generate sound, like for example synthesizers.
Usage
Initialization
Library.init(this) // loads the dynamic link library
val audio = AudioRoot(this)
Creating an audio graph is done following the builder pattern
val testTone = TestTone()
audio.graph = AudioGraph.Builder()
.add(testTone)
.build()
Finally audio is started
audio.start()
Importing this extension exposes node parameters as flows, so creating a slider composable that controls the test tone frequency in the above example is simple:
val frequency by testTone.sineWaveFrequency.valueFlow().collectAsStateWithLifecycle(0f)
Column {
Text(
text = "${frequency.roundToInt()} Hz"
)
Slider(
value = frequency,
valueRange = testTone.sineWaveFrequency.valueRange,
onValueChange = {
testTone.sineWaveFrequency.value = it
}
)
}
Custom DSP
Creating a custom node is done by extending the Kotlin AudioNode and
C++ juce::AudioProcessor classes. The former is a wrapper that handles
all JNI calls and the latter implements the actual DSP. Both must be linked
somehow, this is done by editing nodes.h.
See TestTone.kt
for an example wrapper.
It is also possible to implement custom nodes outside the library namespace by setting up NDK in the parent project and calling the functions defined in maqam.h
Links
A complete example is available here
For a real world app implementing Maqam check our flagship Android app World Piano at the Google Play Store
A similar project named AudioKit is available for iOS
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