Use IIR or IFR LPFs on resample

Author: rochars

CHANGELOG.md

@@ -1,5 +1,16 @@
 # CHANGELOG
 
+## version 10.4.0 - 2020-01-20
+- Default LPF for resample is IIR 
+- Use FIR or IIR LPFs to resample:
+```javascript
+// Will use 'linear' method with a FIR LPF
+wav.toSampleRate(44100, {method: "linear", LPF: true, LPFType: 'FIR'});
+
+// Will use 'linear' method with a IIR LPF, the default
+wav.toSampleRate(44100, {method: "linear", LPF: true});
+```
+
 ## version 10.3.0 - 2020-01-20
 
 ### Features

README.md

@@ -421,6 +421,15 @@ wav.toSampleRate(44100, {method: "sinc", LPF: false});
 wav.toSampleRate(44100, {method: "linear", LPF: true});
 ```
 
+The default LPF is a IIR LPF. You may define what type of LPF will be used by changing the LPFType attribute on the *toSampleRate()* param. You can use **IIR** or **FIR**:
+```javascript
+// Will use 'linear' method with a FIR LPF
+wav.toSampleRate(44100, {method: "linear", LPF: true, LPFType: 'FIR'});
+
+// Will use 'linear' method with a IIR LPF, the default
+wav.toSampleRate(44100, {method: "linear", LPF: true});
+```
+
 #### Changing the sample rate of ADPCM, mu-Law or A-Law
 You need to convert compressed files to standard PCM before resampling:
 

dist/wavefile.js

@@ -405,6 +405,13 @@ <h4>Resampling methods</h4>
 // Will use 'linear' method with LPF
 wav.toSampleRate(44100, {method: &quot;linear&quot;, LPF: true});
 </code></pre>
+<p>The default LPF is a IIR LPF. You may define what type of LPF will be used by changing the LPFType attribute on the <em>toSampleRate()</em> param. You can use <strong>IIR</strong> or <strong>FIR</strong>:</p>
+<pre class="prettyprint source lang-javascript"><code>// Will use 'linear' method with a FIR LPF
+wav.toSampleRate(44100, {method: &quot;linear&quot;, LPF: true, LPFType: 'FIR'});
+
+// Will use 'linear' method with a IIR LPF, the default
+wav.toSampleRate(44100, {method: &quot;linear&quot;, LPF: true});
+</code></pre>
 <h4>Changing the sample rate of ADPCM, mu-Law or A-Law</h4>
 <p>You need to convert compressed files to standard PCM before resampling:</p>
 <p>To resample a mu-Law file:</p>

docs/index.html

@@ -441,8 +441,9 @@ WaveFile.prototype.toSampleRate = function(
     sincFilterSize: 32,
     lanczosFilterSize: 24,
     sincWindow: function(x){},
-    LPForder: 1,
-    LPF: true}) {};
+    LPF: true,
+    LPFType: 'IIR',
+    LPForder: 1}) {};
 
 /**
  * Encode a 16-bit wave file as 4-bit IMA ADPCM.

externs/wavefile.js

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2019 Rafael da Silva Rocha.
+ * Copyright (c) 2014 Florian Markert
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+/**
+ * @fileoverview Butterworth LPF. Based on the Butterworth LPF from Fili.js.
+ * @see https://github.com/rochars/wavefile
+ * @see https://github.com/markert/fili.js
+ */
+
+/**
+ * Butterworth LPF.
+ */
+export class ButterworthLPF {
+  
+  /**
+   * @param {number} order The order of the filter.
+   * @param {number} sampleRate The sample rate.
+   * @param {number} cutOff The cut off frequency.
+   */
+  constructor(order, sampleRate, cutOff) {
+    let filters = [];
+    for (let i = 0; i < order; i++) {
+      filters.push(this.getCoeffs_({
+        Fs: sampleRate,
+        Fc: cutOff,
+        Q: 0.5 / (Math.sin((Math.PI / (order * 2)) * (i + 0.5)))
+      }));
+    }
+    this.stages = [];
+    for (let i = 0; i < filters.length; i++) {
+      this.stages[i] = {
+        b0 : filters[i].b[0],
+        b1 : filters[i].b[1],
+        b2 : filters[i].b[2],
+        a1 : filters[i].a[0],
+        a2 : filters[i].a[1],
+        k : filters[i].k,
+        z : [0, 0]
+      };
+    }
+  }
+
+  /**
+   * @param {number} sample A sample of a sequence.
+   * @return {number}
+   */
+  filter(sample) {
+    let out = sample;
+    for (let i = 0, len = this.stages.length; i < len; i++) {
+      out = this.runStage_(i, out);
+    }
+    return out;
+  }
+
+  getCoeffs_(params) {
+    let coeffs = {};
+    coeffs.z = [0, 0];
+    coeffs.a = [];
+    coeffs.b = [];
+    let p = this.preCalc_(params, coeffs);
+    coeffs.k = 1;
+    coeffs.b.push((1 - p.cw) / (2 * p.a0));
+    coeffs.b.push(2 * coeffs.b[0]);
+    coeffs.b.push(coeffs.b[0]);
+    return coeffs;
+  }
+
+  preCalc_(params, coeffs) {
+    let pre = {};
+    let w = 2 * Math.PI * params.Fc / params.Fs;
+    pre.alpha = Math.sin(w) / (2 * params.Q);
+    pre.cw = Math.cos(w);
+    pre.a0 = 1 + pre.alpha;
+    coeffs.a0 = pre.a0;
+    coeffs.a.push((-2 * pre.cw) / pre.a0);
+    coeffs.k = 1;
+    coeffs.a.push((1 - pre.alpha) / pre.a0);
+    return pre;
+  }
+  
+  runStage_(i, input) {
+    let temp =
+      input * this.stages[i].k - this.stages[i].a1 * this.stages[i].z[0] -
+      this.stages[i].a2 * this.stages[i].z[1];
+    let out =
+      this.stages[i].b0 * temp + this.stages[i].b1 * this.stages[i].z[0] +
+      this.stages[i].b2 * this.stages[i].z[1];
+    this.stages[i].z[1] = this.stages[i].z[0];
+    this.stages[i].z[0] = temp;
+    return out;
+  }
+
+  /**
+   * Reset the filter.
+   */
+  reset() {
+    for (let i = 0; i < this.stages.length; i++) {
+      this.stages[i].z = [0, 0];
+    }
+  }
+}

lib/resampler/butterworth-lpf.js

@@ -29,6 +29,7 @@
 
 import { Interpolator } from './interpolator';
 import { FIRLPF } from './fir-lpf';
+import { ButterworthLPF } from './butterworth-lpf';
 
 const DEFAULT_LPF_USE = {
   'point': false,
@@ -38,10 +39,13 @@ const DEFAULT_LPF_USE = {
 };
 
 const DEFAULT_LPF_ORDER = {
-  'point': 71,
-  'linear': 71,
-  'cubic': 71,
-  'sinc': 71
+  'IIR': 16,
+  'FIR': 71
+};
+
+const DEFAULT_LPF = {
+  'IIR': ButterworthLPF,
+  'FIR': FIRLPF
 };
 
 /**
@@ -73,18 +77,20 @@ export function resample(samples, oldSampleRate, sampleRate, details={}) {
     details.LPF = DEFAULT_LPF_USE[details.method];
   } 
   if (details.LPF) {
+    details.LPFType = details.LPFType || 'IIR';
+    const LPF = DEFAULT_LPF[details.LPFType];
     // Upsampling
     if (sampleRate > oldSampleRate) {
-      let filter = new FIRLPF(
-        details.LPForder || DEFAULT_LPF_ORDER[details.method],
+      let filter = new LPF(
+        details.LPForder || DEFAULT_LPF_ORDER[details.LPFType],
         sampleRate,
         (oldSampleRate / 2));
       upsample_(
         samples, newSamples, interpolator, filter);
     // Downsampling
     } else {
-      let filter = new FIRLPF(
-        details.LPForder || DEFAULT_LPF_ORDER[details.method],
+      let filter = new LPF(
+        details.LPForder || DEFAULT_LPF_ORDER[details.LPFType],
         oldSampleRate,
         sampleRate / 2);
       downsample_(