Android Native アプリで音声が聞こえない

audioManager.mode = AudioManager.MODE_IN_COMMUNICATION
audioManger.isSpeakerphoneOn = true

private var savedAudioMode: Int = AudioManager.MODE_NORMAL
private var savedIsSpeakerPhoneOn: Boolean = false

 override fun onStart() {
    super.onStart()

    val audioManager: AudioManager = getSystemService(Context.AUDIO_SERVICE) as AudioManager

    // 現在の設定値を保存しておく
    savedAudioMode = audioManager.mode
    savedIsSpeakerPhoneOn = audioManager.isSpeakerphoneOn

     audioManager.mode = AudioManager.MODE_IN_COMMUNICATION
     audioManager.isSpeakerphoneOn = true
}

 override fun onStop() {
    super.onStop()

    val audioManager: AudioManager = getSystemService(Context.AUDIO_SERVICE) as AudioManager

    // 保存しておいた値をもとに戻す
    audioManager.mode = savedAudioMode
    audioManager.isSpeakerphoneOn = savedIsSpeakerPhoneOn
}