swift 我录音的时候peakPower没有改变是为什么呀

func configRecordingHUDImageWithPeakPower(peakPower:Float) {
    var imageName = "RecordingSignal00"
    print("===========\(peakPower)")
    switch peakPower {
    case peakPower where peakPower > 0 && peakPower <= 0.1:
      imageName += "1"
      break
    case peakPower where peakPower > 0.1 && peakPower < 0.3:
      imageName += "2"
      break
    case peakPower where peakPower > 0 && peakPower < 0.4:
      imageName += "3"
      break
    case peakPower where peakPower > 0 && peakPower < 0.5:
      imageName += "4"
      break
    case peakPower where peakPower > 0 && peakPower < 0.6:
      imageName += "5"
      break
    case peakPower where peakPower > 0 && peakPower < 0.7:
      imageName += "6"
      break
    case peakPower where peakPower > 0 && peakPower < 0.8:
      imageName += "7"
      break
    default:
      imageName += "4"
      break
    }