降低一个声音的音量，而另一个声音播放

Question

在我的MenuScene.swift中，当我的游戏开始时，我有一系列随机播放的声音：

       let soundNames = [
        "Sound/01.mp3",
        "Sound/02.mp3",
        "Sound/03.mp3"
    ]
    let randomSoundName = soundNames[Int(arc4random_uniform(UInt32(soundNames.count)))]
    _ = self.run(SKAction.playSoundFileNamed(randomSoundName, waitForCompletion: false))

...在我的GameViewController.swift中，我有一个随着游戏开始播放的背景音轨：

        // Start the background music:
    if let musicPath = Bundle.main.path(forResource:
        "Sound/BackgroundMusic.wav", ofType: nil) {
        let url = URL(fileURLWithPath: musicPath)
        do {
            musicPlayer = try AVAudioPlayer(contentsOf: url)
            musicPlayer.numberOfLoops = -1
            musicPlayer.prepareToPlay()
            musicPlayer.play()
        }
        catch { /* Couldn't load music file */ }
    }

当随机声音在其顶部播放时，如何减小背景音轨的音量？