I’m facing a problem in implementing spatial audio effects in my iOS 18 app. I have tried several approaches to achieve 3D audio effect, but the result never felt good enough or it didn’t work at all.

Issue that mostly troubles me is I noticed that AirPods I have don't recognize my app as one having spatial audio. In audio settings it shows "Spatial Audio Not Playing", which makes me think my app doesn't use spatial audio potential.

It might be relevant to mention that I am using a personal team account.

First approach uses AVAudioEnviromentNode with AVAudioEngine. Despite setting the playerNode.position and listener parameters, the spatial effects don’t seem to work. Changing the listenerPosition or playerNode.position has no noticeable impact on playback.

Here's simplified example how i initialize AVAudioEngine:

import Foundation
import AVFoundation

class AudioManager: ObservableObject {
// important class variables
    var audioEngine: AVAudioEngine!
    var environmentNode: AVAudioEnvironmentNode!
    var playerNode: AVAudioPlayerNode!
    var audioFile: AVAudioFile?
...
   //Sound set up
func setupAudio() {
        do {
            let session = AVAudioSession.sharedInstance()
            try session.setCategory(.playback, mode: .default, options: [])
            try session.setActive(true)
        } catch {
            print("Failed to configure AVAudioSession: \(error.localizedDescription)")
        }

        audioEngine = AVAudioEngine()
        environmentNode = AVAudioEnvironmentNode()
        playerNode = AVAudioPlayerNode()
        audioEngine.attach(environmentNode)
        audioEngine.attach(playerNode)
        audioEngine.connect(playerNode, to: environmentNode, format: nil)
        audioEngine.connect(environmentNode, to: audioEngine.mainMixerNode, format: nil)
        environmentNode.listenerPosition = AVAudio3DPoint(x: 0, y: 0, z: 0)
        environmentNode.listenerAngularOrientation = AVAudio3DAngularOrientation(yaw: 0, pitch: 0, roll: 0)
      environmentNode.distanceAttenuationParameters.referenceDistance = 1.0        environmentNode.distanceAttenuationParameters.maximumDistance = 100.0
        environmentNode.distanceAttenuationParameters.rolloffFactor = 2.0
        // example.mp3 is mono sound
        guard let audioURL = Bundle.main.url(forResource: "example", withExtension: "mp3") else {
            print("Audio file not found")
            return
        }

        do {
            audioFile = try AVAudioFile(forReading: audioURL)
        } catch {
            print("Failed to load audio file: \(error)")
        }
   }
...
    //Playing sound
    func playSpatialAudio(pan: Float ) {
        guard let audioFile = audioFile else { return }
        //  left side
        playerNode.position = AVAudio3DPoint(x: pan, y: 0, z: 0)
        playerNode.scheduleFile(audioFile, at: nil, completionHandler: nil)

        do {
            try audioEngine.start()
            playerNode.play()
        } catch {
            print("Failed to start audio engine: \(error)")
        }
...
}    

Second approach is more complex using PHASE - it did better. I’ve made an exemplary app that allows players to move audio source in 3D space. I have added reverb, and sliders changing audio position up to 10 meters each direction from listener but audio seems to only really change left to right (x axis) - again I think it might be trouble with the app not being recognized as spatial (AirPods settings still show “Spatial Audio Not Playing”).

Here's the example setup:

class PHASEAudioController: ObservableObject{
    //Crucial class Variables:
    private var soundSourcePosition: simd_float4x4 = matrix_identity_float4x4
    private var audioAsset: PHASESoundAsset!
    private let phaseEngine: PHASEEngine
    private let params = PHASEMixerParameters()
    private var soundSource: PHASESource
    private var phaseListener:  PHASEListener!
    private var soundEventAsset: PHASESoundEventNodeAsset?

// Initialization of PHASE
init{     
 do {
            let session = AVAudioSession.sharedInstance()
            try session.setCategory(.playback, mode: .default, options: [])

            try session.setActive(true)
        } catch {
            print("Failed to configure AVAudioSession: \(error.localizedDescription)")
        }
        // Init PHASE Engine
        phaseEngine = PHASEEngine(updateMode: .automatic)
        phaseEngine.defaultReverbPreset = .mediumHall
        phaseEngine.outputSpatializationMode = .automatic //nothing helps        
        // Set listener position to (0,0,0) in World space
        let origin: simd_float4x4 = matrix_identity_float4x4
        phaseListener = PHASEListener(engine: phaseEngine)
        phaseListener.transform = origin
        phaseListener.automaticHeadTrackingFlags = .orientation
        try! self.phaseEngine.rootObject.addChild(self.phaseListener)
        do{
            try self.phaseEngine.start();
        }
        catch {
            print("Could not start PHASE engine")
        }
 
        audioAsset = loadAudioAsset()
        // Create sound Source
        // Sphere
        soundSourcePosition.translate(z:3.0)
        let sphere = MDLMesh.newEllipsoid(withRadii: vector_float3(0.1,0.1,0.1), radialSegments: 14, verticalSegments: 14, geometryType: MDLGeometryType.triangles, inwardNormals: false, hemisphere: false, allocator: nil)
        let shape = PHASEShape(engine: phaseEngine, mesh: sphere)
        soundSource = PHASESource(engine: phaseEngine, shapes: [shape])
        soundSource.transform = soundSourcePosition
        print(soundSourcePosition)
        do {
            try phaseEngine.rootObject.addChild(soundSource)
        }
        catch {
            print ("Failed to add a child object to the scene.")
        }
        let simpleModel = PHASEGeometricSpreadingDistanceModelParameters()
        simpleModel.rolloffFactor = rolloffFactor
        soundPipeline.distanceModelParameters = simpleModel
        
        let samplerNode = PHASESamplerNodeDefinition(
            soundAssetIdentifier: audioAsset.identifier,
            mixerDefinition: soundPipeline,
            identifier: audioAsset.identifier + "_SamplerNode")
        samplerNode.playbackMode = .looping
        do {soundEventAsset = try
            phaseEngine.assetRegistry.registerSoundEventAsset(
            rootNode: samplerNode,
            identifier: audioAsset.identifier + "_SoundEventAsset")
        } catch {
            print("Failed to register a sound event asset.")
            soundEventAsset = nil
        }
}

//Playing sound
 func playSound(){
        // Fire new sound event with currently set properties
        guard let soundEventAsset else { return }
        
        params.addSpatialMixerParameters(
            identifier: soundPipeline.identifier,
            source: soundSource,
            listener: phaseListener)
        let soundEvent = try! PHASESoundEvent(engine: phaseEngine,
                                              assetIdentifier: soundEventAsset.identifier,
                                              mixerParameters: params)
        soundEvent.start(completion: nil)
    }
...
}

Also I have experimented with RealityKit, but I hope to find a solution without using AR view, PHASE seems to be best option if it worked as intended.

What I expect I hope my app will position audio in 3D space correctly in all axes like in some other spatial apps available on iOS and app will be recognized as spatial audio enabled app by e.g. AirPods.