Hello. We are trying to get audio volume from microphone. We have 2 questions. 1. Can anyone tell me about AVAudioEngine.InputNode.volume? AVAudioEngine.InputNode.volume Return 0 in the silence, Return float type value within 1.0 depending on the volume are expected work, but it looks 1.0 (default value) is returned at any time. Which case does it return 0.5 or 0? Sample code is below. Microphone works correctly. // instance member private var engine: AVAudioEngine! private var node: AVAudioInputNode! // start method self.engine = .init() self.node = engine.inputNode engine.prepare() try! engine.start() // volume getter print(\(self.node.volume)) 2. What is the best practice to get audio volume from microphone? Requirements are: Without AVAudioRecorder. We use it for streaming audio. it should withstand high frequency access. Testing info device: iPhone XR OS version: iOS 18 Best Regards.

Watch OS11 My recording play gets paused when watch I turned down. It was not happening in previous versions. In my app I recorded my recording. And When I play it in my app, it was playing good in debug mode(when Xcode is connected) could not debug. Otherwise, it was automatically paused(when my wrist is down or inactivity time is elapsed) I want it to be continued.

I need to find a way to allow recording from the mic while outputting two different sound streams to two different devices (speaker and headphones). I've done a fair bit of reading around using AVAudioSession.Category.multiroute but haven't found any modern examples. @theanalogkid posted a nice example using obj-C nine years ago, but others have noted that the code isn't readily translatable to Swift. To make matters worse, this is one of the very few examples on how to properly use multirouting. The official documentation is lacking, to say the least, and the WWDC 2012 session is, well, old enough to attend middle school and be a Taylor Swift fan, but definitely not in Swift. The few relevant forum posts here are spread over this middle schooler's life span and likely outdated, with most having no responses other than the poster's own plightful echo. They don't paint a pretty picture of .multiroute's health, with a recent poster noting that volume buttons don't work in this mode, contacting DTS and finding that there's no fix; another finding that it just doesn't work for certain devices, etc. Audio is giving me enough of a headache so I'd like to avoid slogging through this if possible. .multiroute feels like the developer mode of AVAudioSession, but without documentation. tl;dr - Without using .multiroute, is there a way to allow an app to output two different devices while simultaneously recording audio? If .multiroute is the only way to achieve this, can someone give me a quick rundown of how this category works?

Description: I am developing a recording-only application that supports background recording using AVAudioEngine. The app segments the recording into 60-second files for further processing. For example, a 10-minute recording results in ten 60-second files. Problem: The application functions as expected in the background. However, after the app receives an interruption (such as a phone call) and the interruption ends, I can successfully restart the recording. The problem arises when the app then transitions to the background; it fails to restart the recording. Specifically, after ending the call and transitioning the app to the background, the app encounters an error and is unable to restart AVAudioSession and AVAudioEngine. The only resolution is to close and restart the app, which is not ideal for user experience. Steps to Reproduce: 1. Start recording using AVAudioEngine. 2. The app records and saves 60-second segments. 3. Receive an interruption (e.g., an incoming phone call). 4. End the call. 5. Transition the app to the background. 6. Transition the app to the foreground and the session will be activated again. 7. Attempt to restart the recording. Expected Behavior: The app should resume recording seamlessly after the interruption and background transition. Actual Behavior: The app fails to restart AVAudioSession and AVAudioEngine, resulting in a continuous error. The recording cannot be resumed without closing and reopening the app. How I’m Starting the Recording: Configuration: internal func setAudioSessionCategory() { do { try audioSession.setCategory( .playAndRecord, mode: .default, options: [.defaultToSpeaker, .mixWithOthers, .allowBluetooth] ) } catch { debugPrint(error) } } internal func setAudioSessionActivation() { if UIApplication.shared.applicationState == .active { do { try audioSession.setPrefersNoInterruptionsFromSystemAlerts(true) try audioSession.setActive(true, options: .notifyOthersOnDeactivation) if audioSession.isInputGainSettable { try audioSession.setInputGain(1.0) } try audioSession.setPreferredIOBufferDuration(0.01) try setBuiltInPreferredInput() } catch { debugPrint(error) } } } Starting AVAudioEngine: internal func setupEngine() { if callObserver.onCall() { return } inputNode = audioEngine.inputNode audioEngine.attach(audioMixer) audioEngine.connect(inputNode, to: audioMixer, format: AVAudioFormat.validInputAudioFormat(inputNode)) } internal func beginRecordingEngine() { audioMixer.removeTap(onBus: 0) audioMixer.installTap(onBus: 0, bufferSize: 1024, format: AVAudioFormat.validInputAudioFormat(inputNode)) { [weak self] buffer, _ in guard let self = self, let file = self.audioFile else { return } write(file, buffer: buffer) } audioEngine.prepare() do { try audioEngine.start() recordingTimer = Timer.scheduledTimer(withTimeInterval: recordingInterval, repeats: true) { [weak self] _ in self?.handleRecordingInterval() } } catch { debugPrint(error) } } On the try audioEngine.start() call, I receive error code 561145187 in the catch block. Logs/Error Messages: • Error code: 561145187 Request: I would appreciate any guidance or solutions to ensure the app can resume recording after interruptions and background transitions without requiring a restart. Thank you for your assistance.

Hi there community, First and foremost, a big thank you to everyone who takes the time to read this. TL;DR: How, if even possible, can I record multiple audio streams simultaneously on an iOS application (iPad/iPhone)? I'm working on a recorder for the iPad to gather data for a machine learning project focused on speech recognition. Our goal is to capture extensive speech data, which requires recording from multiple microphones. Specifically, I need to record from all mics connected to our Scarlett 4i4 audio interface and, most importantly, also record from the built-in mic on the iPad or iPhone at the same time. As a newcomer to Swift development, I initially explored AVAudioRecorder. However, I quickly realized that it only supports one active audio node at a time, making multi-channel recording impossible. (perhaps you can proof me wrong, would make my day) Next, I transitioned to using AVAudioEngine, but encountered the same limitation: I couldn't manage to get input nodes for both the built-in mic and the Scarlett interface channels simultaneously. The application started behaving oddly, often resulting in identical audio data being recorded across all files. Determined to find a solution, I delved deeper into the Core Audio framework, specifically using Audio Toolbox. My approach involved creating and configuring multiple Audio Units, each corresponding to a different audio input device. Here's a brief overview of my current implementation: Listing Available Input Devices: I used AVAudioSession to enumerate all available input devices. Creating Audio Units: For each device, I created an Audio Unit and attempted to configure it for recording. Setting Up Callbacks: I set up input and output callbacks to handle the audio processing. Despite my efforts over the last few days, I haven't had much success. The callbacks for the Audio Units don't seem to be invoked correctly, and I'm struggling to achieve simultaneous multi-channel recording. Below is a snippet of my latest attempt: let audioUnitCallback: AURenderCallback = { ( inRefCon: UnsafeMutableRawPointer, ioActionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>, inTimeStamp: UnsafePointer<AudioTimeStamp>, inBusNumber: UInt32, inNumberFrames: UInt32, ioData: UnsafeMutablePointer<AudioBufferList>? ) -> OSStatus in guard let ioData = ioData else { return noErr } print("Input callback invoked") let audioUnit = inRefCon.assumingMemoryBound(to: AudioUnit.self).pointee var bufferList = AudioBufferList( mNumberBuffers: 1, mBuffers: AudioBuffer( mNumberChannels: 1, mDataByteSize: 0, mData: nil ) ) let status = AudioUnitRender(audioUnit, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, &bufferList) if status != noErr { print("AudioUnitRender failed: \(status)") return status } // Copy rendered data to output buffer let buffer = UnsafeMutableAudioBufferListPointer(ioData)[0] buffer.mData?.copyMemory(from: bufferList.mBuffers.mData!, byteCount: Int(bufferList.mBuffers.mDataByteSize)) buffer.mDataByteSize = bufferList.mBuffers.mDataByteSize print("Rendered audio data") return noErr } let outputCallback: AURenderCallback = { ( inRefCon: UnsafeMutableRawPointer, ioActionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>, inTimeStamp: UnsafePointer<AudioTimeStamp>, inBusNumber: UInt32, inNumberFrames: UInt32, ioData: UnsafeMutablePointer<AudioBufferList>? ) -> OSStatus in guard let ioData = ioData else { return noErr } print("Output callback invoked") // Process the output data if needed return noErr } In essence, I'm stuck and in need of guidance. Has anyone here successfully implemented multi-channel recording on iOS, especially involving both built-in microphones and external audio interfaces? Any shared experiences, insights, or suggestions on how to proceed would be immensely appreciated. Thank you once again for your time and assistance!

Hello, I hope this message finds you well. I am currently working on a Unity-based iOS application that requires continuous microphone input while also producing sound outputs. For this we need to use iOS echo cancellation, so some sounds need to be played via the iOS layer w/ echo cancellation, I am manually setting up the Audio Session after the app starts. Using the .playAndRecord mode of AVAudioSession. However, I am facing an issue where the volume of the sound output is inconsistent across different iOS devices and scenarios. The process is quite simple, for each AudioClip we are about to play via unity, we copy the buffer data to our iOS Swift layer, which then does all the processing then plays the audio via the native layer. Here are the specific issues I am encountering: The volume level for the game sound effects fluctuate between a normal audible volume and a very low volume. The sound output behaves differently depending on whether the app is launched with the device at full volume or on mute, and if the app is put into background and in foreground afterwards. The volume inconsistency affects my game negatively, as it is very hard to hear some audios, regardless of the device or its initial volume state. I have followed the basic setup for AVAudioSession as per the documentation, but the inconsistencies persist. I'm also aware that Unity uses FMOD to set up the audio routing in iOS, we configure our custom routing after that. We tried tweaking the output volume prior to playing an audio so there isn't much discrepancy, this seems to align the output volume, however there is still some places where the volume is super low, I've looked into the waveforms in Unity and they all seem consistent, there is no reason why the volume would take a dip. private var audioPlayer = AVAudioPlayerNode() @objc public func Play() { audioPlayer.volume = AVAudioSession.sharedInstance().outputVolume * 0.25 audioPlayer.play() } We also explored changing the audio session options to see if we had any luck but unfortunately nothing has changed. private func ConfigAudioSession() { let audioSession = AVAudioSession.sharedInstance(); do { try audioSession.setCategory(.playAndRecord, options: [.mixWithOthers, .allowBluetooth, .defaultToSpeaker]); try audioSession.setMode(.spokenAudio) try audioSession.setActive(true); } catch { //Treat error } } Could anyone provide guidance or suggest best practices to ensure a stable and consistent volume output in this scenario? Any advice on this issue would be greatly appreciated. Thank you in advance for your help!

Hi there, I am encountering an issue in my project which utilizes a speech recognizer and occasionally plays audio files. The problem arises when I configure the AVAudioSession and enable voice processing. The system volume changes unexpectedly and becomes uncontrollable. Specifically, the volume is excessively loud on iPhone but quite low on iPad let audioSession = AVAudioSession.sharedInstance() try audioSession.setCategory(.playAndRecord, mode: .default, options: [.defaultToSpeaker, .allowBluetooth, .interruptSpokenAudioAndMixWithOthers]) try audioSession.setActive(true, options: .notifyOthersOnDeactivation) try audioEngine.inputNode.setVoiceProcessingEnabled(true) try audioEngine.outputNode.setVoiceProcessingEnabled(true) I have provided a sample project here: Sample Project. To reproduce the issue, please follow these steps on a real device: Click on "Play recording" to hear the sound at normal volume. Click on "Start recording" to set up the category and speech recognizer. Click on "Stop recording" to stop the recording. Click on "Play recording" again and observe that the sound volume has changed. Thank you for your assistance.

Hello, I am currently developing an application for audiogram testing. What methods can I use to obtain the dB values of headphone levels in real-time?

I'm using AVAudioEngine to play AVAudioPCMBuffers. I'd like to synchronize some events with the playback. For example if the audio's frame position is >= some point && less than some point trigger some code. So I'm looking at - (void)installTapOnBus:(AVAudioNodeBus)bus bufferSize:(AVAudioFrameCount)bufferSize format:(AVAudioFormat * __nullable)format block:(AVAudioNodeTapBlock)tapBlock; Now I have frame positions calculated (predetermined before audio is scheduled I already made all necessary computations) . So I just need to fire code at certain points during playback: [playerNode installTapOnBus:bus bufferSize:bufferSize format:format block:^(AVAudioPCMBuffer * _Nonnull buffer, AVAudioTime * _Nonnull when) { //Inspect current audio here and fire... }]; [playerNode scheduleBuffer:fullbuffer atTime:startTime options:0 completionCallbackType:AVAudioPlayerNodeCompletionDataPlayedBack completionHandler:^(AVAudioPlayerNodeCompletionCallbackType callbackType) { // some code is here, not important to this question. }]; The problem I'm having is figuring out at what point in full buffer I'm at within the tap block. The tap block passes chunks (not the full audio buffer). I tried using the when parameter of the block to calculate the frame position relative to the entire audio but have be unsuccessful so far. I'm assuming the when parameter is relative to the buffer passed in the tap block (not my entire audio buffer I scheduled). Not installing a tap and just using a timer before scheduling my fullBuffer has given me good results but I'd rather avoid using a timer if possible and use sample time.

Hello everyone, I'm relatively new to iOS development, and I'm currently working on a Flutter plugin package. I want to use the AVFAudio package to load instrument sounds from an SF2 file into different channels. Specifically, I'd like to load individual instruments from the SF2 file onto separate channels. However, I've been struggling to find a way to achieve this. Could someone guide me on how to load SF2 instrument sounds into different channels using AVFAudio? I've tried various combinations of parameters (program number, soundbank MSB, and soundbank LSB), but none seem to work. If anyone has experience with AVFAudio and SF2 files, I'd greatly appreciate your help. Perhaps there's a proven approach or a way to determine the correct values for these parameters? Should I use a soundfont editor to inspect specific values within the SF2 file? Thank you in advance for any assistance! Best regards, Melih

Hi everybody, I'm trying to use the multi input of an usb device using the AVAudioEngine. My aim is to connect different inputNode channels to 2 or more different audionode (f.e. mixer). I'm able to get a spefic input channel from the engine inputNode with OSStatus err = AudioUnitSetProperty(avEngine.inputNode.audioUnit, kAudioOutputUnitProperty_ChannelMap, kAudioUnitScope_Output, 1, outputChannelMap, propSize); but this will change the routing to all the input node and to all the destination mixer nodes. How to send channel 1 of inputNode to a mixerNode1 and channel 2 to another mixerNode2?

I have a PCM audio buffer (AVAudioPCMFormatInt16). When I try to play it using AVPlayerNode / AVAudioEngine an exception is thrown: "[[busArray objectAtIndexedSubscript:(NSUInteger)element] setFormat:format error:&nsErr]: returned false, error Error Domain=NSOSStatusErrorDomain Code=-10868 (related thread https://forums.developer.apple.com/forums/thread/700497?answerId=780530022#780530022) If I convert the buffer to AVAudioPCMFormatFloat32 playback works. My questions are: Does AVAudioEngine / AVPlayerNode require AVAudioPCMBuffer to be in the Float32 format? Is there a way I can configure it to accept another format instead for my application? If 1 is YES is this documented anywhere? If 1 is YES is this required format subject to change at any point? Thanks! I was looking to watch the "AVAudioEngine in Practice" session video from WWDC 2014 but I can't find it anywhere (https://forums.developer.apple.com/forums/thread/747008).

My project has uses an AVAudioEngine with a very simple setup: A Speech recognizer running on a tap on the engine's input with separate AVAudioPlayerNodes handling playback. try session.setCategory(.playAndRecord, mode: .default, options: []) try session.setActive(true, options: .notifyOthersOnDeactivation) try session.setAllowHapticsAndSystemSoundsDuringRecording(true) filePlayerNode ---> engine.mainMixerNode bufferPlayerNode --> engine.mainMixerNode engine.mainMixerNode --> engine.outputNode //bufferPlayer.scheduleBuffer() is called on its own queue The input works fine since the buffers can be collected into a file and plays back correctly, and also because the recognizer works fine; but when I try to play the live audio by sending the buffer to the bufferPlayer on this or another device, the buffer audio plays at a very low volume, sometimes with severe distortions. If I lower the sample rate via AVAudioConverter, the distortions get worse. I've tried experimenting with the AVAudioSession category options, having separate AVAudioEngines, and much, much more, yet I still haven't figured this out. It's gotten to the point where I've fixed almost all the arcane and minor issues in my audio system, yet I still can't play back my voice properly. The ability to both play and record simultaneously is a basic feature of phones--when on speaker mode, a phone doesn't need to behave like a walkie-talkie. In my mind, it's inconceivable that the relatively new AVAudioEngine doesn't have a implementation for this, since the main issue (feedback loops) can be dealt with via a simple primitive circuit. Live video chat apps like FaceTime wouldn't be possible without this, yet to my surprise I found no answers online (what I did find were articles explaining how to write a file while playback is occurring). Is there truly no way to do this on AVAudioEngine? Am I missing something fundamental? Any pointers would be greatly appreciated

Hi everyone, I was working on some code that involves recording audio with AVAudioEngine and got an issue that just crashes the app: EXC_BREAKPOINT Exception 6, Code 1, Subcode 4304279688 +0x009888 AudioRecordModule.setupAudioEngine +0x009788 AudioRecordModule.setupAudioEngine +0x00c5bc AudioRecordModule.handleConfigurationChange Below is the relevant code in the Recorder class. public class AudioRecordModule: Module { private var audioEngine: AVAudioEngine? private func startRecording(options recordingOptions: RecordingOptions) { try AVAudioSession.sharedInstance().setCategory(.playAndRecord, options: .mixWithOthers) try AVAudioSession.sharedInstance().setActive(true) outputFormat = AVAudioFormat( commonFormat: recordingOptions.bitDepth == 32 ? .pcmFormatInt32 : .pcmFormatInt16, sampleRate: Double(recordingOptions.sampleRate), channels: AVAudioChannelCount(recordingOptions.channels), interleaved: true )! let fileUri = URL(string: recordingOptions.fileUri)! let formatSettings: [String: Any] = [ AVFormatIDKey: kAudioFormatMPEG4AAC, AVSampleRateKey: recordingOptions.sampleRate, AVNumberOfChannelsKey: recordingOptions.channels, AVEncoderBitRateStrategyKey: AVAudioBitRateStrategy_Constant, AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue, ] self.recordedFile = try AVAudioFile( forWriting: fileUri, settings: formatSettings, commonFormat: outputFormat.commonFormat, interleaved: outputFormat.isInterleaved ) if !hadSetupNotification { setupNotifications() } } func handleConfigurationChange() { DispatchQueue.main.async { self.releaseAudioEngine() self.setupAudioEngine() if self.state == "recording" { // we could attempt to keep recording do { try self.audioEngine?.start() } catch { self.internalPauseRecording() self.sendInterruptEvent() } } } } func setupNotifications() { nc.addObserver( forName: Notification.Name.AVAudioEngineConfigurationChange, object: nil, queue: nil ) { [weak self] _ in guard let weakself = self else { return } if weakself.state != "inactive" { weakself.handleConfigurationChange() } } } private func setupAudioEngine() { self.audioEngine = nil let audioEngine = AVAudioEngine() self.audioEngine = audioEngine let inputNode = audioEngine.inputNode let inputFormat = inputNode.inputFormat(forBus: 0) let converter = AVAudioConverter(from: inputFormat, to: outputFormat)! inputNode.installTap(onBus: 0, bufferSize: 1024, format: inputFormat) { (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in do { let inputBlock: AVAudioConverterInputBlock = { _, outStatus in outStatus.pointee = AVAudioConverterInputStatus.haveData return buffer } let frameCapacity = AVAudioFrameCount(self.outputFormat.sampleRate) * buffer.frameLength / AVAudioFrameCount(buffer.format.sampleRate) let outputBuffer = AVAudioPCMBuffer( pcmFormat: self.outputFormat, frameCapacity: frameCapacity )! var error: NSError? converter.convert(to: outputBuffer, error: &error, withInputFrom: inputBlock) if let error = error { throw error } else { try self.recordedFile?.write(from: outputBuffer) } } catch { print(error) } } } private func releaseAudioEngine() { if let audioEngine = self.audioEngine { audioEngine.inputNode.removeTap(onBus: 0) audioEngine.stop() } audioEngine = nil } } Beside that, the record module works normally. It is just the configuration change that it does not handle well. I understand that when configuration changes, I need to reinit the audio engine to have the correct input format (since the new config/audio device can have different sample rate and such). If I don't do that, the app also crashes perhaps due to the mismatch. AVAudioRecorder is not an option for me. Thank you for your help.

As the title suggests I am using AVAudioEngine for SpeechRecognition input & AVAudioPlayer for sound output. Apple says in this talk https://developer.apple.com/videos/play/wwdc2019/510 that the setVoiceProcessingEnabled function very usefully cancels the output from speaker to the mic. I set voiceProcessing on the Input and output nodes. It seems to work however the volume is low, even when the system volume is turned up. Any solution to this would be much appreciated.

Hello, I'm facing an issue with Xcode 15 and iOS 17: it seems impossible to get AVAudioEngine's audio input node to work on simulator. inputNode has a 0ch, 0kHz input format, connecting input node to any node or installing a tap on it fails systematically. What we tested: Everything works fine on iOS simulators <= 16.4, even with Xcode 15. Nothing works on iOS simulator 17.0 on Xcode 15. Everything works fine on iOS 17.0 device with Xcode 15. More details on this here: https://github.com/Fesongs/InputNodeFormat Any idea on this? Something I'm missing? Thanks for your help 🙏 Tom PS: I filed a bug on Feedback Assistant, but it usually takes ages to get any answer so I'm also trying here 😉

Hi there, I'm having some trouble with AVAudioMixerNode only working when there is a single input, and outputting silence or very quiet buzzing when >1 input node is connected. My setup has voice processing enabled, input going to a sink, and N source nodes going to the main mixer node, going to the output node. In all cases I am connecting nodes in the graph with the same declared format: 48kHz 1 channel Float32 PCM. This is working great for 1 source node, but as soon as I add a second it breaks. I can reproduce this behaviour in the SignalGenerator sample, when the same format is used everywhere. Again, it'll work fine with 1 source node even in this configuration, but add another and there's silence. Am I doing something wrong with formats here? Is this expected? As I understood it with voice processing on and use of a mixer node I should be able to use my own format essentially everywhere in my graph? My SignalGenerator modified repro example follows: import Foundation import AVFoundation // True replicates my real app's behaviour, which is broken. // You can remove one source node connection // to make it work even when this is true. let showBrokenState: Bool = true // SignalGenerator constants. let frequency: Float = 440 let amplitude: Float = 0.5 let duration: Float = 5.0 let twoPi = 2 * Float.pi let sine = { (phase: Float) -> Float in return sin(phase) } let whiteNoise = { (phase: Float) -> Float in return ((Float(arc4random_uniform(UINT32_MAX)) / Float(UINT32_MAX)) * 2 - 1) } // My "application" format. let format: AVAudioFormat = .init(commonFormat: .pcmFormatFloat32, sampleRate: 48000, channels: 1, interleaved: true)! // Engine setup. let engine = AVAudioEngine() let mainMixer = engine.mainMixerNode let output = engine.outputNode try! output.setVoiceProcessingEnabled(true) let outputFormat = engine.outputNode.inputFormat(forBus: 0) let sampleRate = Float(format.sampleRate) let inputFormat = format var currentPhase: Float = 0 let phaseIncrement = (twoPi / sampleRate) * frequency let srcNodeOne = AVAudioSourceNode { _, _, frameCount, audioBufferList -> OSStatus in let ablPointer = UnsafeMutableAudioBufferListPointer(audioBufferList) for frame in 0..<Int(frameCount) { let value = sine(currentPhase) * amplitude currentPhase += phaseIncrement if currentPhase >= twoPi { currentPhase -= twoPi } if currentPhase < 0.0 { currentPhase += twoPi } for buffer in ablPointer { let buf: UnsafeMutableBufferPointer<Float> = UnsafeMutableBufferPointer(buffer) buf[frame] = value } } return noErr } let srcNodeTwo = AVAudioSourceNode { _, _, frameCount, audioBufferList -> OSStatus in let ablPointer = UnsafeMutableAudioBufferListPointer(audioBufferList) for frame in 0..<Int(frameCount) { let value = whiteNoise(currentPhase) * amplitude currentPhase += phaseIncrement if currentPhase >= twoPi { currentPhase -= twoPi } if currentPhase < 0.0 { currentPhase += twoPi } for buffer in ablPointer { let buf: UnsafeMutableBufferPointer<Float> = UnsafeMutableBufferPointer(buffer) buf[frame] = value } } return noErr } engine.attach(srcNodeOne) engine.attach(srcNodeTwo) engine.connect(srcNodeOne, to: mainMixer, format: inputFormat) engine.connect(srcNodeTwo, to: mainMixer, format: inputFormat) engine.connect(mainMixer, to: output, format: showBrokenState ? inputFormat : outputFormat) // Put the input node to a sink just to match the formats and make VP happy. let sink: AVAudioSinkNode = .init { timestamp, numFrames, data in .zero } engine.attach(sink) engine.connect(engine.inputNode, to: sink, format: showBrokenState ? inputFormat : outputFormat) mainMixer.outputVolume = 0.5 try! engine.start() CFRunLoopRunInMode(.defaultMode, CFTimeInterval(duration), false) engine.stop()