DCFilter = function(audiolet, coefficient) {
    AudioletNode.call(this, audiolet, 2, 1);

    // Same number of output channels as input channels
    this.linkNumberOfOutputChannels(0, 0);

    this.coefficient = new AudioletParameter(this, 1, coefficient || 0.995);

    // Delayed values
    this.xValues = [];
    this.yValues = [];
}
Filter for leaking DC offset.  Maths is taken from
https://ccrma.stanford.edu/~jos/filters/DC_Blocker.html

**Inputs**

- Audio
- Filter coefficient

**Outputs**

- Filtered audio

**Parameters**

- coefficient The filter coefficient.  Linked to input 1.

@constructor
@extends AudioletNode
@param {Audiolet} audiolet The audiolet object.
@param {Number} [coefficient=0.995] The initial coefficient.