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我正在解析一个 midi 文件，然后使用MIKMIDI将 midi 事件发送到连接的合成器，但我将事件时间戳四舍五入到整数秒而不是更具体的毫秒。我需要帮助准确计算时间。谢谢。// 前面定义的 class Note { var symbol:String var octave:Int var midiValue:Int var duration:Float }

let BPM:Double = 75
// Ode to joy simplified
var song:[Note] = [
  Note(symbol: "E", octave: 5),
  Note(symbol: "E", octave: 5),
  Note(symbol: "F", octave: 5),
  Note(symbol: "G", octave: 5),

  Note(symbol: "G", octave: 5),
  Note(symbol: "F", octave: 5),
  Note(symbol: "E", octave: 5),
  Note(symbol: "D", octave: 5),

  Note(symbol: "C", octave: 5),
  Note(symbol: "C", octave: 5),
  Note(symbol: "D", octave: 5),
  Note(symbol: "E", octave: 5),

  Note(symbol: "E", octave: 5, duration: 3/8),
  Note(symbol: "D", octave: 5, duration: 1/8),
  Note(symbol: "D", octave: 5, duration: 1/2)
]
let now = NSDate()
let totalDuration:Double = 0
for note:Note in song {
  let fullNoteValue:Double = (60000 / BPM) * 0.001 * 4
  let noteDuration:Double = fullNoteValue * Double(note.duration)
  let timestamp = now.dateByAddingTimeInterval(noteDuration + totalDuration)
  MidiDevice.sharedInstance().playNoteOn(note.midiValue, withTimestamp: timestamp)
  totalDuration += noteDuration
}

MidiDevice playNoteOn 定义

- (void)playNoteOn:(NSInteger)note withTimestamp:(MIDITimeStamp)timestamp {
  MIKMutableMIDINoteOnCommand *noteOn = [MIKMutableMIDINoteOnCommand commandForCommandType:MIKMIDICommandTypeNoteOn];
  noteOn.note = (NSUInteger) note;
  noteOn.velocity = 100;
  noteOn.timestamp = timestamp
  // noteOn.midiTimestamp = timestamp;

  NSMutableArray *destinations = [NSMutableArray array];

  for (MIKMIDIDevice *device in [[MIKMIDIDeviceManager sharedDeviceManager] availableDevices]) {
    for (MIKMIDIEntity *entity in [device.entities valueForKeyPath:@"@unionOfArrays.destinations"]) {
      [destinations addObject:entity];
    }
  }

  //  NSArray *destinations = [self.device.entities valueForKeyPath:@"@unionOfArrays.destinations"];
  if (![destinations count]) return;
  for (MIKMIDIDestinationEndpoint *destination in destinations) {
    NSError *error = nil;
    if(![self.deviceManager sendCommands:@[noteOn] toEndpoint:destination error:&error]) {
      NSLog(@"Unable to send command %@ to endpoint %@: %@", noteOn, destination, error);
    }
  }
}

如何将此时间戳更改为可以使用 MIDISend() 或 MIKMIDI 发送的准确时间戳？

4

1 回答 1

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您正在使用不兼容的时间测量。首先你这样说：

let now = NSDate()
let timestamp = now.dateByAddingTimeInterval(noteDuration + totalDuration)

但是然后你把它交给 MIDI 设备：

 MidiDevice.sharedInstance().playNoteOn(note.midiValue, withTimestamp: timestamp)

但事实证明，这里的时间戳应该是一个 MIDITimeStamp：

(void)playNoteOn:(NSInteger)note withTimestamp:(MIDITimeStamp)timestamp {

MIDITimeStamp 不是 NSDate！MIDITimeStamp 基于mach_absolute_time(), 一种完全不同的度量。NSDate 被测量为 NSTimeInterval，它是从某个固定的参考日期时间开始的 Double 计数秒数。马赫绝对时间是一个巨大的整数，从计算机开机时开始计算纳秒！

所以，要成功调用这个方法，就需要去掉NSDate，用MIDI时间来思考。

于 2015-09-15T04:18:28.333 回答