录制的声音听不清楚

Question

我正在制作卡拉OK应用程序。如果没有插入耳机，我的应用程序工作正常。 （我的声音和背景音乐记录在一起）。它是成功的。所以，我合并了插入耳机时录制的背景音乐和语音...如果我合并两首歌曲我听到两种声音都很清楚。但问题是如果我录制了我的声音和音乐我可以听到声音我的声音非常低

func mixAudio()
{
    let currentTime = CFAbsoluteTimeGetCurrent()
    let composition = AVMutableComposition()
    let compositionAudioTrack = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: kCMPersistentTrackID_Invalid)
    compositionAudioTrack.preferredVolume = 0.8
    let avAsset = AVURLAsset.init(URL: soundFileURL, options: nil)
    print("\(avAsset)")
    var tracks = avAsset.tracksWithMediaType(AVMediaTypeAudio)
    let clipAudioTrack = tracks[0]
    do {
        try compositionAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, avAsset.duration), ofTrack: clipAudioTrack, atTime: kCMTimeZero)
    }
    catch _ {
    }
    let compositionAudioTrack1 = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: kCMPersistentTrackID_Invalid)
    compositionAudioTrack.preferredVolume = 0.8

    let avAsset1 = AVURLAsset.init(URL: soundFileURL1)
    print(avAsset1)


    var tracks1 = avAsset1.tracksWithMediaType(AVMediaTypeAudio)
    let clipAudioTrack1 = tracks1[0]
    do {
        try compositionAudioTrack1.insertTimeRange(CMTimeRangeMake(kCMTimeZero, avAsset1.duration), ofTrack: clipAudioTrack1, atTime: kCMTimeZero)
    }
    catch _ {
    }
    var paths = NSSearchPathForDirectoriesInDomains(.LibraryDirectory, .UserDomainMask, true)
    let CachesDirectory = paths[0]
    let strOutputFilePath = CachesDirectory.stringByAppendingString("/newone.mov")
    print(" strOutputFilePath is \n \(strOutputFilePath)")

    let requiredOutputPath = CachesDirectory.stringByAppendingString("/newone.m4a")
    print(" requiredOutputPath is \n \(requiredOutputPath)")

    soundFile1 = NSURL.fileURLWithPath(requiredOutputPath)
    print(" OUtput path is \n \(soundFile1)")
    do {

        try NSFileManager.defaultManager().removeItemAtURL(soundFile1)
    }
    catch _ {
    }
    let exporter = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A)
    exporter!.outputURL = soundFile1
    exporter!.outputFileType = AVFileTypeAppleM4A

    exporter!.exportAsynchronouslyWithCompletionHandler
        {() -> Void in
            print(" OUtput path is \n \(requiredOutputPath)")
            print("export complete: \(CFAbsoluteTimeGetCurrent() - currentTime)")

    do
    {
        print(self.soundFile1)
        print(" OUtput path is \n \(requiredOutputPath)")


        self.wasteplayer = try AVAudioPlayer(contentsOfURL: self.soundFile1)
        self.wasteplayer.numberOfLoops = 0
        self.wasteplayer.play()


    }

    catch _ {
    }

    }