Adding DC Filter Module

Tone/component/filter/DCFilter.ts

@@ -0,0 +1,105 @@
+import { ToneAudioNode, ToneAudioNodeOptions } from "../../core/context/ToneAudioNode";
+import { optionsFromArguments } from "../../core/util/Defaults";
+import { Gain } from "../../core/context/Gain";
+
+export type DCFilterOptions = ToneAudioNodeOptions; 
+
+/**
+ * 
+ * Tone.DCFilter is a filter that removes DC offsets that are not centerd at zero
+ * It is essentially a 1st order highpass alike filter, (Similar to a [[Tone.OnePoleFilter]]),
+ * with a frequency around 20Hz or lower using a IIRFilterNode at a fixed value where a = -0.995 using this formula:
+ * 
+ *  y[n] = x[n] - x[n-1] + a * y[n-1]
+ * 
+ *  or
+ *            1 - z⁻¹
+ *  H(z) =  -----------
+ *          1 - a * z⁻¹
+ * 
+ * This is useful for removing any clippling, popping or any other unsual sounds that
+ * exceeds the nominal audio range of [1, -1] or between [1, 0] and [0, -1].
+ * This can be also useful for applying DC offset filtering from nodes like 
+ * [[Tone.WaveShaper]] or [[Tone.Oscillator]] etc, for some fine tuning or to prevent clipping in the waveform.
+ * 
+ * References:
+ * * https://www.musicdsp.org/en/latest/Filters/135-dc-filter.html
+ * * https://ccrma.stanford.edu/~jos/fp/DC_Blocker_Frequency_Response.html
+ * * http://peabody.sapp.org/class/dmp2/lab/dcblock/
+ * 
+ * 
+ * @example
+ * const filter = new Tone.DCFilter().toDestination();
+ * cosnt abs = new Tone.Abs();
+ * const osc = new Tone.Oscillator();
+ * 
+ * osc.chain(abs, filter);
+ * osc.start();
+ * 
+ * 
+ * @category Component
+ */
+
+export class DCFilter extends ToneAudioNode<DCFilterOptions> {
+    readonly name: string = "DCFilter";
+
+    readonly input: Gain;
+    readonly output: Gain;
+
+    private _filter: IIRFilterNode;
+
+    /**
+     * No need for params because filter is a fixed value.
+     * This is better because in a lot of DAWs in music, (especially professionals),
+     * usally has a DC filter that dosen't require a lot of functionality (besides toggling on amd off).
+     * 
+     *
+     * However, If you would like more parameters,
+     * then please create a new issue or PR (Pull Request) to Tone.js requesting this.
+     * Please make sure to include @Hazmatron7 and @tambien
+     *
+     * Please note that these are the only available parameters to add:
+     *      - changable parameter for a instead of a fixed value. Range: [0, 0.999], default = 0.995.
+     *      - inverse the phase direction by swapping the feedback coefficients from [1, -a] to [-1, a].
+     *
+     */
+
+    constructor(options?: Partial<DCFilterOptions>)
+    constructor() {
+        super(optionsFromArguments(DCFilter.getDefaults(), arguments, []);
+
+        this.input = new Gain({context: this.context});
+        this.output = new Gain({context: this.context});
+
+        // a = -0.995
+        this._filter = this.context.createIIRFilter([1, -1], [1, -0.995]);
+
+        this.input.chain(this._filter, this.output);
+
+    }
+
+    static getDefaults(): DCFilterOptions {
+        return Object.assign(ToneAudioNode.getDefaults(), {});
+    }
+
+    getFrequencyResponse(len = 128): Float32Array {
+        const freqValues = new Float32Array(len);
+        for (let i = 0; i < len; i++) {
+            const norm = Math.pow(i / len, 2);
+            const freq = norm * (20000 - 20) + 20;
+            freqValues[i] = freq;
+        }
+        const magValues = new Float32Array(len);
+        const phaseValues = new Float32Array(len);
+        this._filter.getFrequencyResponse(freqValues, magValues, phaseValues);
+        return magValues;
+    }
+
+    dispose(): this {
+        super.dispose();
+        this.input.dispose();
+        this.output.dispose();
+        this._filter.disconnect();
+        return this;
+    }
+}

Tone/component/index.ts

@@ -30,6 +30,7 @@ export * from "./envelope/AmplitudeEnvelope";
 export * from "./envelope/Envelope";
 export * from "./envelope/FrequencyEnvelope";
 
+export * from "./filter/DCFilter";
 export * from "./filter/EQ3";
 export * from "./filter/Filter";
 export * from "./filter/OnePoleFilter";