AVAudiounit：我无法播放具有延迟效果的声音

Question

我是 Objective c 的新手，并尝试编写一个可以播放带有效果的声音的程序，例如混响或延迟。不幸的是，我只能播放声音，但没有效果。我现在被困了3天，找不到解决方案。有谁可以告诉我做错了什么？ 我试过这段代码，但它根本没有声音：

- (void)viewDidLoad {
    [super viewDidLoad];
    AVAudioEngine *engine = [AVAudioEngine new];
    AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];

    playerA.volume = 0.5;


    NSURL *Mia1url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"MIA1" ofType:@"m4a"]];

    AVAudioFile *MIA1 = [[AVAudioFile alloc] initForReading:Mia1url error:nil];
    AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:MIA1.processingFormat frameCapacity:1024];
    [MIA1 readIntoBuffer:buffer error:nil];

    AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
    delay.delayTime = 100;
    delay.wetDryMix = 90;

    [engine attachNode:playerA];
    [engine attachNode:delay];

    [engine connect: playerA to: delay format:MIA1.processingFormat];
    [engine connect: delay to: engine.mainMixerNode format: MIA1.processingFormat];

    [playerA scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];

    [engine prepare];
    [engine startAndReturnError:nil];

    [playerA play];
}

之后我尝试了这段代码，但声音只是没有效果：

- (void)viewDidLoad {
    [super viewDidLoad];
    AVAudioEngine *engine = [AVAudioEngine new];
    AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];

    playerA.volume = 0.5;

    NSURL *Mia1url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"MIA1" ofType:@"m4a"]];

    AVAudioFile *MIA1 = [[AVAudioFile alloc] initForReading:Mia1url error:nil];
    AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:MIA1.processingFormat frameCapacity:1024];
    [MIA1 readIntoBuffer:buffer error:nil];

    AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
    delay.delayTime = 100;
    delay.wetDryMix = 90;

    [engine attachNode:playerA];
    [engine attachNode:delay];

    [engine connect: playerA to: delay format:MIA1.processingFormat];
    [engine connect: delay to: engine.mainMixerNode format: MIA1.processingFormat];

    [playerA scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];

    [engine prepare];
    [engine startAndReturnError:nil];

    //change
    self.playerA = [[AVAudioPlayer alloc] initWithContentsOfURL:Mia1url error:nil];

    //change from [playerA play] to:
    [self.playerA play];
}

Answer 1

你忘了实例化你的对象：

//AVAudioEngine *engine; // no instance exists. 
AVAudioEngine *engine = [AVAudioEngine new]; 
AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];

...

AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
...

另外，playerA 只需在使用前初始化一次。

要深入挖掘，您可能需要查看Apples code samples。