Sonix Overview

Sonix is the audio engine module of VoxaTrace, providing:

• Audio Playback — Play audio files with pitch shifting and tempo control
• Recording — Record audio to M4A or MP3 formats
• Multi-track Mixing — Mix multiple audio tracks with individual controls
• Metronome — Programmable metronome with visual feedback
• MIDI Synthesis — Play MIDI notes using SoundFont instruments

Sonix in Action

Mixing Multiple Tracks

Track 1 (Backing):  ████████████████████████████████  vol: 0.8
Track 2 (Vocals):   ░░░░████████████████░░░░░░░░░░░░  vol: 1.0
Track 3 (Guide):    ████████████████████████████████  vol: 0.3 (muted)
Track 4 (Click):    █░░░█░░░█░░░█░░░█░░░█░░░█░░░█░░░  vol: 0.5
                    ─────────────────────────────────
Output:             Mixed audio to speakers

Pitch Shifting

Original:     C4 ──── D4 ──── E4 ──── F4 ────
              262 Hz  294 Hz  330 Hz  349 Hz

+2 semitones: D4 ──── E4 ──── F#4 ─── G4 ────
              294 Hz  330 Hz  370 Hz  392 Hz

The melody stays the same, just in a different key.

Recording Pipeline

Microphone
    │
    ▼
┌─────────────────┐
│ SonixRecorder   │──── audioBuffers (real-time for visualization)
│                 │──── level (VU meter)
│ ┌─────────────┐ │
│ │ MP3 Encoder │ │──── output.mp3
│ └─────────────┘ │
└─────────────────┘

Key Features

Playback

val player = SonixPlayer.create("song.mp3")
player.play()
player.pitch = 2f     // +2 semitones (higher key)
player.tempo = 0.8f   // 80% speed (slower)
player.seek(30_000)   // Jump to 30 seconds

Feature	Range
Formats	M4A, MP3, WAV
Pitch shifting	-12 to +12 semitones
Tempo control	0.5x to 2x speed
Looping	Any region

Recording

val recorder = SonixRecorder.create(
    SonixRecorderConfig.Builder()
        .format(AudioFormat.MP3)
        .outputPath("recording.mp3")
        .build()
)
recorder.start()
// ... user sings ...
recorder.stop()

Feature	Options
Output formats	M4A (AAC), MP3
Sample rates	16kHz, 44.1kHz, 48kHz
Echo cancellation	Built-in support
Background recording	Supported

Multi-track Mixing

Perfect for karaoke apps that need backing track + vocal guide + click track:

val mixer = SonixMixer.create()
mixer.loadTrack(0, "backing.mp3")
mixer.loadTrack(1, "vocal_guide.mp3")
mixer.setVolume(0, 0.8f)  // Backing at 80%
mixer.setVolume(1, 0.3f)  // Guide quiet
mixer.play()

Feature	Specification
Simultaneous tracks	Up to 8
Per-track controls	Volume, pan, solo, mute
Synchronization	Sample-accurate

Metronome

val metronome = SonixMetronome.create(bpm = 120)
metronome.onBeat { beat, isAccent ->
    // Update UI on each beat
}
metronome.start()

Feature	Range
BPM	40 – 240
Time signatures	Any
Custom sounds	Supported

MIDI Synthesis

Generate vocal guides or accompaniment from MIDI:

val synth = SonixMidiSynthesizer.create("piano.sf2")
synth.noteOn(channel = 0, note = 60, velocity = 100) // Middle C
synth.noteOff(channel = 0, note = 60)

Feature	Specification
SoundFont support	.sf2 files
Channels	16 (MIDI standard)
Events	Note on/off, program change, pitch bend

Next Steps

API Reference

• SonixPlayer — Audio playback with pitch shifting and tempo control
• SonixRecorder — Record audio to M4A, MP3, or WAV
• SonixMixer — Multi-track mixing with per-track volume
• SonixMetronome — Programmable click track
• SonixDecoder — Decode audio files to raw PCM
• SonixEncoder — Encode PCM to compressed formats
• SonixResampler — Sample rate conversion
• SonixMidiSynthesizer — MIDI to audio synthesis
• SonixLessonSynthesizer — Lesson audio from svara sequences
• Utilities — Parser, frames, and error types

Guides

• Playing Audio Guide — In-depth SonixPlayer guide