VoxaTrace/com.musicmuni.voxatrace.sonix/SonixMixer

SonixMixer

Multi-track audio mixer with synchronized playback.

Quick Start

Kotlin

val mixer = SonixMixer.create()
mixer.addTrack("backing", "/path/to/backing.mp3")  // Auto-decodes
mixer.addTrack("vocal", "/path/to/vocal.mp3")
mixer.play()

// Control individual tracks
mixer.setTrackVolume("vocal", 0.5f)  // Reduce vocal volume
mixer.fadeTrackVolume("vocal", 0f, 2000)  // Fade out over 2 seconds

// Release when done
mixer.release()

Swift

let mixer = SonixMixer.create(
    config: .default,
    audioSession: .playback
)
await mixer.addTrack(name: "backing", filePath: "/path/to/backing.mp3")
await mixer.addTrack(name: "vocal", filePath: "/path/to/vocal.mp3")
mixer.play()

// Control individual tracks
mixer.setTrackVolume(name: "vocal", volume: 0.5)
mixer.fadeTrackVolume(name: "vocal", targetVolume: 0, durationMs: 2000)

// Release when done
mixer.release()

Builder Pattern (Advanced)

Kotlin

val config = SonixMixerConfig.Builder()
    .loopCount(3)
    .onPlaybackComplete { println("All loops done!") }
    .onLoopComplete { index -> println("Completed loop $index") }
    .build()
val mixer = SonixMixer.create(config)

StateFlows

StateFlow	Type	Description
`currentTime`	Long	Current playback time in ms
`isPlaying`	Boolean	True while playing
`error`	SonixError?	Error state

Platform Notes

iOS

Uses AVAudioEngine for synchronized playback
Automatically configures audio session

Android

Software-mixes all tracks into a single AudioTrack (sample-locked by construction)
Automatically configures audio focus

Common Pitfalls

addTrack is suspend: Call from coroutine or use addTrack(name, data, rate, channels)
Forgetting to release: Call release() when done
Track names must be unique: Adding a track with same name replaces it
Different sample rates: Tracks are automatically resampled to match

Types

Companion

object Companion

PlaybackListener

interface PlaybackListener

Listener interface for playback events.

Properties

asPlaybackInfoProvider

open override val asPlaybackInfoProvider: PlaybackInfoProvider

This mixer as a PlaybackInfoProvider for recorder sync.

completedLoops

val completedLoops: Int

Number of completed loop iterations.

currentTime

open override val currentTime: StateFlow<Long>

Current playback time in milliseconds.

duration

val duration: Long

Total duration in milliseconds (based on longest track).

error

val error: StateFlow<SonixError?>

Error state, null if no error.

isPlaying

open override val isPlaying: StateFlow<Boolean>

Whether playback is currently active.

loopCount

var loopCount: Int

Current loop count setting.

outputRoute

val outputRoute: SonixOutputRoute

The route this mixer's audio is currently going out on.

pitch

var pitch: Float

Pitch shift in semitones (tempo-preserving), applied to every track.

Functions

addTrack

suspend fun addTrack(name: String, filePath: String): Boolean

Add track from file path (auto-decodes).

fun addTrack(name: String, data: ByteArray, sampleRate: Int, channels: Int, pitchExempt: Boolean = false): Boolean

Add track from raw PCM data (for advanced use cases).

audibleTimeMsAtWallNanos

open override fun audibleTimeMsAtWallNanos(wallNanos: Long): Long

Audible player time for a wall moment, with the output-latency compensation for the live outputRoute subtracted (SonixPlayer.compensationForRoute) — identical to SonixPlayer.audibleTimeMsAtWallNanos. Both PlaybackController impls must apply it: the live-eval scorer anchors student frames through whichever one plays the reference, and practice plays the reference in this mixer (accompaniment + reference + shruti shift). Compensating only the bare player left the mixer path — i.e. every real practice take — uncompensated.

fadeTrackVolume

fun fadeTrackVolume(name: String, targetVolume: Float, durationMs: Long)

Fade a track's volume smoothly from current to target.

fun fadeTrackVolume(name: String, startVolume: Float, endVolume: Float, durationMs: Long)

Fade a track's volume smoothly from start to end value.

getTrackNames

fun getTrackNames(): List<String>

Get names of all loaded tracks.

hasTrack

fun hasTrack(name: String): Boolean

Check if a track is loaded.

pause

open override fun pause()

Pause playback of all tracks.

play

open override fun play()

Start playback of all tracks.

release

open override fun release()

Release all resources.

removeTrack

fun removeTrack(name: String)

Remove a track from the mixer.

reset

fun reset()

Reset playback position to the beginning without stopping.

seek

open override fun seek(positionMs: Long)

Seek all tracks to a specific position.

setPlaybackListener

fun setPlaybackListener(listener: SonixMixer.PlaybackListener?)

Set a listener for playback events.

setReferenceTrack

fun setReferenceTrack(name: String)

Designate the reference track — typically the lesson track a live evaluator scores against. While one is set, currentTime and audibleTimeMsAtWallNanos ride the DAC-presentation clock of its playback (on Android the single mix sink all tracks share; on iOS the reference player node), so accompaniment and evaluation live on one clock. Without one, time falls back to a wall-clock estimate.

setTrackVolume

fun setTrackVolume(name: String, volume: Float)

Set volume for a specific track.

stop

fun stop()

Stop playback and reset to beginning.

SonixMixer

Quick Start

Kotlin

Swift

Builder Pattern (Advanced)

Kotlin

StateFlows

Platform Notes

iOS

Android

Common Pitfalls

See also

Types

Properties

Functions