iOS 11.3下使用AKMIDISampler加载SoundFont无音频输出求助

Let’s walk through the common issues in your code and fix them one by step:

1. Missing SoundFont File Extension #

Your code references GigaPiano but doesn’t include the file extension. SoundFonts typically use .sf2 (Standard SoundFont 2) or .sfz formats. If your file is named GigaPiano.sf2, you need to include that extension in the path. Also, using Bundle.main.path(forResource:) is a safer way to locate bundle files than constructing the path manually:

let soundPath = Bundle.main.path(forResource: "GigaPiano", ofType: "sf2", inDirectory: "Sounds")!

Double-check that the SoundFont file is added to your Xcode project and marked as part of your target — if it’s not copied into the app bundle, the path will be invalid even with the correct extension.

2. You’re Not Triggering Any MIDI Notes #

Loading the SoundFont only prepares the sampler to play sounds, but you haven’t sent any MIDI note-on messages to it! To test audio output, add a simple note trigger after loading the SoundFont:

// Play middle C (MIDI note 60) at full velocity
midiSampler.play(noteNumber: 60, velocity: 127, channel: 0)

If you want the note to stop after a moment, add a delay and send a note-off:

DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
    self.midiSampler.stop(noteNumber: 60, channel: 0)
}

3. Audio Session Permissions & Configuration #

iOS 10+ requires explicit permission to access the audio system, and you need to set the correct audio session category for playback. Add this code before starting AudioKit:

do {
    try AKSettings.setSession(category: .playback)
} catch {
    print("Failed to set audio session category: \(error)")
}

Also, make sure you’ve added the NSAudioUsageDescription key to your Info.plist file (this tells iOS why your app needs audio access — without it, the audio session might fail to activate):

<key>NSAudioUsageDescription</key>
<string>Playback of sampled audio sounds</string>

4. AudioKit Startup & Connection Order #

Your current order has minor inconsistencies — it’s better to set AudioKit.output before starting the mixer, and ensure all connections are finalized before starting AudioKit.

Full Corrected Code #

import AudioKit

class AudioPlayer {
    let mixer = AKMixer()
    var midiSampler: AKMIDISampler!
    var samplerVolume: AKBooster!

    init() {
        // Initialize audio components
        midiSampler = AKMIDISampler()
        samplerVolume = AKBooster(midiSampler, gain: 1.0) // Explicit gain setting for clarity
        
        // Build audio chain
        mixer.connect(input: samplerVolume)
        AudioKit.output = mixer
        
        // Configure audio session for playback
        do {
            try AKSettings.setSession(category: .playback)
        } catch {
            print("Audio session configuration error: \(error)")
        }
        
        // Load SoundFont and trigger test note
        guard let soundPath = Bundle.main.path(forResource: "GigaPiano", ofType: "sf2", inDirectory: "Sounds") else {
            print("SoundFont file not found")
            return
        }
        
        do {
            try midiSampler.loadSoundFont(soundPath, preset: 0, bank: 0)
            print("SoundFont loaded successfully")
            
            // Play test note
            midiSampler.play(noteNumber: 60, velocity: 127, channel: 0)
            
            // Stop note after 2 seconds
            DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
                self.midiSampler.stop(noteNumber: 60, channel: 0)
            }
        } catch {
            print("Error loading soundfont: \(error)")
        }
        
        // Start AudioKit
        do {
            try AudioKit.start()
            print("AudioKit started successfully")
        } catch {
            print("AudioKit start error: \(error)")
        }
    }
}

Additional Checks #

• Verify that your device/simulator isn’t muted (check the physical mute switch and volume level).
• If using the simulator, note that audio performance can be inconsistent — test on a physical iOS 11.3 device if possible.
• Ensure you’re using a compatible version of AudioKit for iOS 11.3 (older versions might have bugs with newer SDKs, but AKMIDISampler should work reliably on 11.3).

内容的提问来源于stack exchange，提问作者jbm