我正在构建一个 iPhone 应用程序，它通过以“caf”格式播放单独录制的吉他音符来生成随机吉他音乐。这些音符的持续时间从 3 秒到 11 秒不等，具体取决于延音量。

我最初使用 AVAudioPlayer 进行播放，在模拟器中以 120 bpm 播放 16 分音符，它唱得很漂亮，但在我的手机上，只要我
将速度提高到 60 bpm 以上，只演奏 1/4 音符，它跑得像条狗，跟不上时间。我的兴高采烈是很短暂的。

为了减少延迟，我尝试使用 Apple MixerHost 项目作为音频引擎的模板，通过 Audio Units 实现播放，但是在我用 bolt 固定并连接所有东西后，仍然出现错误的访问错误。

经过几个小时的努力，我放弃了这种想法，转而使用 Novocaine 音频引擎。

我现在遇到了一堵砖墙，试图将它连接到我的模型。

在最基本的层面上，我的模型是一个 Neck 对象，其中包含一个 NSDictionary 的 Note 对象。

每个 Note 对象都知道它在吉他琴颈上的弦和品格，并包含自己的 AVAudioPlayer。

根据用户偏好中选择的琴颈尺寸，我构建了一个包含 122 个音符(6 弦 x 22 品)或 144 个音符(6 弦 x 24 品)的半音吉他琴颈。

我使用这些音符作为我的单一事实点，因此音乐引擎生成的所有标量音符都是指向这个半音音符桶的指针。

@interface Note : NSObject <NSCopying>
{
    NSString *name;
    AVAudioPlayer *soundFilePlayer;
    int stringNumber;
    int fretNumber; 
}

- (void)runMusicGenerator:(NSNumber *)counter
{
if (self.isRunning) {
    Note *NoteToPlay;
    // pulseRate is the time interval between beats
    // staticNoteLength = 1/4 notes, 1/8th notes, 16th notes, etc.

    float delay = self.pulseRate / [self grabStaticNoteLength];

    // user setting to play single, double or triplet notes. 
    if (self.beatCounter == CONST_BEAT_COUNTER_INIT_VAL) {
        NoteToPlay = [self.GuitarNeck generateNoteToPlayNext];
    } else {
        NoteToPlay = [self.GuitarNeck cloneNote:self.GuitarNeck.NoteToPlayNow];
    }

    self.GuitarNeck.NoteToPlayNow = NoteToPlay;

    [self callOutNoteToPlay];

    [self performSelector:@selector(runDrill:) withObject:NoteToPlay afterDelay:delay];
}

- (Note *)generateNoteToPlayNext
{
    if ((self.musicPaused) || (self.musicStopped)) {
        // grab the root note on the string to resume
        self.NoteToPlayNow = [self grabRootNoteForString];

        //reset the flags
        self.musicPaused = NO;
        self.musicStopped = NO;
    } else {
        // Set NoteRingingOut to NoteToPlayNow
        self.NoteRingingOut = self.NoteToPlayNow;

        // Set NoteToPlaNowy to NoteToPlayNext
        self.NoteToPlayNow = self.NoteToPlayNext;
        if (!self.NoteToPlayNow) {
            self.NoteToPlayNow = [self grabRootNoteForString];

            // now prep the note's audio player for playback
            [self.NoteToPlayNow.soundFilePlayer prepareToPlay];
        }        
    }

    // Load NoteToPlayNext
        self.NoteToPlayNext = [self generateRandomNote];
    }

    - (void)callOutNoteToPlay
    {    
        self.GuitarNeck.NoteToPlayNow.soundFilePlayer.delegate = (id)self;
        [self.GuitarNeck.NoteToPlayNow.soundFilePlayer setVolume:1.0];
        [self.GuitarNeck.NoteToPlayNow.soundFilePlayer setCurrentTime:0];
        [self.GuitarNeck.NoteToPlayNow.soundFilePlayer play];
    }

- (AVAudioPlayer *)buildStringNotePlayer:(NSString *)nameOfNote
{
    NSString *soundFileName = @"S";
    soundFileName = [soundFileName stringByAppendingString:[NSString stringWithFormat:@"%d", stringNumber]];
    soundFileName = [soundFileName stringByAppendingString:@"F"];

    if (fretNumber < 10) {
        soundFileName = [soundFileName stringByAppendingString:@"0"];
    }
    soundFileName = [soundFileName stringByAppendingString:[NSString stringWithFormat:@"%d", fretNumber]];

    NSString *soundPath = [[NSBundle mainBundle] pathForResource:soundFileName ofType:@"caf"];
    NSURL *fileURL = [NSURL fileURLWithPath:soundPath];
    AVAudioPlayer *audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL error:nil];

    return notePlayer;
}

Novocaine *audioManager = [Novocaine audioManager];
[audioManager setOutputBlock:^(float *audioToPlay, UInt32 numSamples, UInt32 numChannels) {
    // All you have to do is put your audio into "audioToPlay".
}];

// AUDIO FILE READING OHHH YEAHHHH
// ========================================
NSURL *inputFileURL = [[NSBundle mainBundle] URLForResource:@"TLC" withExtension:@"mp3"];

fileReader = [[AudioFileReader alloc]
              initWithAudioFileURL:inputFileURL
              samplingRate:audioManager.samplingRate
              numChannels:audioManager.numOutputChannels];

[fileReader play];
fileReader.currentTime = 30.0;

[audioManager setOutputBlock:^(float *data, UInt32 numFrames, UInt32 numChannels)
{
    [fileReader retrieveFreshAudio:data numFrames:numFrames numChannels:numChannels];
    NSLog(@"Time: %f", fileReader.currentTime);
}];

最佳答案

Novocaine 无需手动设置 RemoteIO AudioUnit，让您的生活更轻松。这包括不得不痛苦地填充一堆 CoreAudio 结构并提供一堆回调，例如这个音频处理回调。
static OSStatus PerformThru(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData);
相反，Novocaine 在其实现中处理它，然后调用您通过执行此操作设置的 block 。
[audioManager setOutputBlock: ^(float *audioToPlay, UInt32 numSamples, UInt32 numChannels){} ];
无论你写什么audioToPlay被玩。

[audioManager setOutputBlock:^(float *data, UInt32 numFrames, UInt32 numChannels){
    static int count = 0;
    for(int i=0; i<numFrames; ++i){
        //Mono mix each sample of each sound together. Since result can be 4x louder, divide the total amp by 4. 
        //You should be using `vDSP_vadd` from the accelerate framework for added performance.
        data[count] = (guitarC[count] + guitarE[count] + guitarG[count] + guitarB[count]) * 0.25;
        if(++count >= 44100) count = 0;    //Plays the mix for 1 sec
    }
}];

关于iphone - 在音频应用程序中使用诺卡因，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13291119/