Swift：尝试将语音更改为 iPhone 的声音时，iPhone 的音量很低

我正在尝试语音识别示例。如果我开始通过麦克风识别我的语音，那么我会尝试获取已识别文本的 iPhone 声音。这是工作。不过，声音太小了。你能指导我吗？

而不是，如果我尝试进行简单的按钮操作，AVSpeechUtterance代码，音量正常。

之后，如果我去startRecognise()方法，音量太低。

My Code

func startRecognise()
{
let audioSession = AVAudioSession.sharedInstance()  //2
    do
    {
        try audioSession.setCategory(AVAudioSessionCategoryPlayAndRecord)
        try audioSession.setMode(AVAudioSessionModeDefault)
        try audioSession.setMode(AVAudioSessionModeMeasurement)
        try audioSession.setActive(true, with: .notifyOthersOnDeactivation)
        try AVAudioSession.sharedInstance().overrideOutputAudioPort(AVAudioSessionPortOverride.speaker)
    }
    catch
    {
        print("audioSession properties weren't set because of an error.")
    }
    recognitionRequest = SFSpeechAudioBufferRecognitionRequest()
    guard let inputNode = audioEngine.inputNode else {
        fatalError("Audio engine has no input node")
    }
    guard let recognitionRequest = recognitionRequest else {
        fatalError("Unable to create an SFSpeechAudioBufferRecognitionRequest object")
    }
    recognitionRequest.shouldReportPartialResults = true
    recognitionTask = speechRecognizer.recognitionTask(with: recognitionRequest, resultHandler: { (result, error) in
        if result != nil
        {
            let lastword = result?.bestTranscription.formattedString.components(separatedBy: " ").last
            if lastword == "repeat" || lastword == "Repeat"{
                self.myUtterance2 = AVSpeechUtterance(string: "You have spoken repeat")
                self.myUtterance2.rate = 0.4
                self.myUtterance2.volume = 1.0
                self.myUtterance2.pitchMultiplier = 1.0
                self.synth1.speak(self.myUtterance2)
                // HERE VOICE IS TOO LOW. 
            }
        }
    })
    let recordingFormat = inputNode.outputFormat(forBus: 0)  //11
    inputNode.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) { (buffer, when) in
    self.recognitionRequest?.append(buffer)
    }
    audioEngine.prepare()
    do 
    {
        try audioEngine.start()
    } 
    catch 
    {
        print("audioEngine couldn't start because of an error.")
    }
}

我的按钮操作

func buttonAction()
{
   self.myUtterance2 = AVSpeechUtterance(string: "You are in button action")
   self.myUtterance2.rate = 0.4
   self.myUtterance2.volume = 1.0
   self.myUtterance2.pitchMultiplier = 1.0
   self.synth1.speak(self.myUtterance2)
   // Before going for startRecognise() method, 
   //I tried with buttonAction(), 
   //this time volume is normal. 
   //After startRecognise() method call, volume is too low in both methods.
}

最后，我得到了解决方案。

func startRecognise()
{
let audioSession = AVAudioSession.sharedInstance()  //2
    do
    {
        try audioSession.setCategory(AVAudioSessionCategoryPlayAndRecord)
        try audioSession.setMode(AVAudioSessionModeDefault)
        //try audioSession.setMode(AVAudioSessionModeMeasurement)
        try audioSession.setActive(true, with: .notifyOthersOnDeactivation)
        try AVAudioSession.sharedInstance().overrideOutputAudioPort(AVAudioSessionPortOverride.speaker)
    }
    catch
    {
        print("audioSession properties weren't set because of an error.")
    }

    ... 
}

一旦我评论了这一行，try audioSession.setMode(AVAudioSessionModeMeasurement)，音量工作正常。