     /// Four letter unique description of the node
     public static let ComponentDescription = AudioComponentDescription(appleEffect: kAudioUnitSubType_HighPassFilter)
 
-    private var mixer: AKMixer
+    private var mixer = AKMixer()
     private var au: AUWrapper
 
     /// Cutoff Frequency (Hz) ranges from 10 to 22050 (Default: 6900)

    public override func detach() {
        stop()

        var nodes: [AVAudioNode] = [inputMixer.avAudioNode,
                                    mixer.avAudioNode,
                                    internalEffect]

        if let inputGain = inputGain {
            nodes.append(inputGain.avAudioNode)
        }

        if let effectGain = effectGain {
            nodes.append(effectGain.avAudioNode)
        }

        AKManager.detach(nodes: nodes)
    }

        self.cutoffFrequency = cutoffFrequency
        self.resonance = resonance

        let effect = _Self.effect
        internalEffect = effect
        au = AUWrapper(effect)

        super.init(avAudioNode: mixer.avAudioNode)

        inputGain.volume = 0
        effectGain.volume = 1

        if let input = input {
            input >>> inputMixer
            input >>> inputGain
            input >>> effectGain
        }
        effectGain >>> effect >>> mixer
        inputGain >>> mixer

        au[kHipassParam_CutoffFrequency] = cutoffFrequency
        au[kHipassParam_Resonance] = resonance
