fix(spectralflux): use magnitude spectrum rather than real component of complex spectrum

.github/workflows/build.yml

@@ -7,23 +7,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [
-            # Disabled because with typescript, the 10.x build fails by running out
-            # of heap space. I can't figure out how to increase heap size on the build
-            # but since we're dropping support for 10.x soon, I think this is fine.
-            # Tests still run on all the other versions, and we publish from 16.x now,
-            # so we I think we're fine to disable it for the next few releases.
-            # See you in 2035.
-            #
-            # https://github.com/meyda/meyda/pull/908/checks?check_run_id=3090204396
-            # 10.x,
-            12.x,
-            13.x,
-            14.x,
-            15.x,
-            16.x,
-            17.x,
-          ]
+        node-version: [12.x, 14.x, 15.x, 16.x, 17.x]
 
     steps:
       - uses: actions/checkout@v1

.github/workflows/merge-build.yml

@@ -3,6 +3,7 @@ on:
   push:
     branches:
       - main
+      - v6
 
 jobs:
   build:

__tests__/extractors/positiveFlux.ts

@@ -0,0 +1,41 @@
+import TestData from "../TestData";
+
+// Setup
+var positiveFlux = require("../../dist/node/extractors/positiveFlux");
+
+describe("positiveFlux", () => {
+  test("should return correct Positive Flux value", (done) => {
+    var en = positiveFlux({
+      ampSpectrum: TestData.VALID_AMPLITUDE_SPECTRUM.map((e) => e * 0.8),
+      previousAmpSpectrum: TestData.VALID_AMPLITUDE_SPECTRUM,
+    });
+
+    expect(en).toEqual(2.8276224855864956e-8);
+
+    done();
+  });
+
+  test.skip("should throw an error when passed an empty object", (done) => {
+    try {
+      var en = positiveFlux({});
+    } catch (e) {
+      done();
+    }
+  });
+
+  test.skip("should throw an error when not passed anything", (done) => {
+    try {
+      var en = positiveFlux();
+    } catch (e) {
+      done();
+    }
+  });
+
+  test.skip("should throw an error when passed something invalid", (done) => {
+    try {
+      var en = positiveFlux({ signal: "not a signal" });
+    } catch (e) {
+      done();
+    }
+  });
+});

__tests__/extractors/spectralFlux.ts

@@ -0,0 +1,43 @@
+import TestData from "../TestData";
+
+// Setup
+var spectralFlux = require("../../dist/node/extractors/spectralFlux");
+
+describe("spectralFlux", () => {
+  test("should return correct Spectral Flux value", (done) => {
+    var en = spectralFlux({
+      ampSpectrum: TestData.VALID_AMPLITUDE_SPECTRUM,
+      previousAmpSpectrum: TestData.VALID_AMPLITUDE_SPECTRUM.map(
+        (e) => e * 0.8
+      ),
+    });
+
+    expect(en).toEqual(6.8073007097613e-8);
+
+    done();
+  });
+
+  test.skip("should throw an error when passed an empty object", (done) => {
+    try {
+      var en = spectralFlux({});
+    } catch (e) {
+      done();
+    }
+  });
+
+  test.skip("should throw an error when not passed anything", (done) => {
+    try {
+      var en = spectralFlux();
+    } catch (e) {
+      done();
+    }
+  });
+
+  test.skip("should throw an error when passed something invalid", (done) => {
+    try {
+      var en = spectralFlux({ signal: "not a signal" });
+    } catch (e) {
+      done();
+    }
+  });
+});

docs/audio-features.md

@@ -81,8 +81,8 @@ To use RMS in applications where you expect a ceiling on each audio feature, we
 `spectralFlux`
 
 - _Description_: A measure of how quickly the spectrum of a signal is changing. It is calculated by computing the difference between the current spectrum and that of the previous frame.
-- _What Is It Used For_: Often corresponds to perceptual "roughness" of a sound. Can be used for example, to determine the timbre of a sound.
-- _Range_: Starts at `0.0`. This has no upper range as it depends on the input signal.
+- _What Is It Used For_: Often corresponds to perceptual "roughness" of a sound. Can be used for example, to determine the timbre of a sound, and onset detection.
+- _Range_: Starts at `0.0`. The upper bound is equal to the square root of the buffer size.
 
 ### Spectral Slope
 

package.json

@@ -71,7 +71,7 @@
     "wav": "^1.0.2"
   },
   "engines": {
-    "node": "^10 || ^12 || ^13 || ^14 || ^15 || ^16 || ^17"
+    "node": "^12 || ^14 || ^15 || ^16 || ^17"
   },
   "jest": {
     "preset": "ts-jest",

src/extractors/positiveFlux.ts

@@ -0,0 +1,27 @@
+import { normalizeToOne } from "../utilities";
+
+export default function ({
+  ampSpectrum,
+  previousAmpSpectrum,
+}: {
+  ampSpectrum: Float32Array;
+  previousAmpSpectrum: Float32Array;
+}): number {
+  if (!previousAmpSpectrum) {
+    return 0;
+  }
+
+  const normalizedMagnitudeSpectrum = normalizeToOne(ampSpectrum);
+  const previousNormalizedMagnitudeSpectrum =
+    normalizeToOne(previousAmpSpectrum);
+
+  let sf = 0;
+  for (let i = 0; i < normalizedMagnitudeSpectrum.length; i++) {
+    let x =
+      Math.abs(normalizedMagnitudeSpectrum[i]) -
+      Math.abs(previousNormalizedMagnitudeSpectrum[i]);
+    sf += Math.pow(Math.max(x, 0), 2);
+  }
+
+  return Math.sqrt(sf);
+}

src/extractors/spectralFlux.ts

@@ -1,24 +1,26 @@
-// This file isn't being typechecked at all because there are major issues with it.
-// See #852 for details. Once that's merged, this file should be typechecked.
-// @ts-nocheck
+import { normalizeToOne } from "../utilities";
+
 export default function ({
-  signal,
-  previousSignal,
-  bufferSize,
+  ampSpectrum,
+  previousAmpSpectrum,
 }: {
-  signal: Float32Array;
-  previousSignal: Float32Array;
-  bufferSize: number;
+  ampSpectrum: Float32Array;
+  previousAmpSpectrum: Float32Array;
 }): number {
-  if (typeof signal !== "object" || typeof previousSignal != "object") {
-    throw new TypeError();
+  if (!previousAmpSpectrum) {
+    return 0;
   }
 
+  const normalizedMagnitudeSpectrum = normalizeToOne(ampSpectrum);
+  const previousNormalizedMagnitudeSpectrum =
+    normalizeToOne(previousAmpSpectrum);
+
   let sf = 0;
-  for (let i = -(bufferSize / 2); i < signal.length / 2 - 1; i++) {
-    x = Math.abs(signal[i]) - Math.abs(previousSignal[i]);
-    sf += (x + Math.abs(x)) / 2;
+  for (let i = 0; i < normalizedMagnitudeSpectrum.length; i++) {
+    let x =
+      normalizedMagnitudeSpectrum[i] - previousNormalizedMagnitudeSpectrum[i];
+    sf += Math.pow(x, 2);
   }
 
-  return sf;
+  return Math.sqrt(sf);
 }

src/featureExtractors.ts

@@ -15,6 +15,7 @@ import mfcc from "./extractors/mfcc";
 import chroma from "./extractors/chroma";
 import powerSpectrum from "./extractors/powerSpectrum";
 import spectralFlux from "./extractors/spectralFlux";
+import positiveFlux from "./extractors/positiveFlux";
 
 let buffer = function (args) {
   return args.signal;
@@ -49,4 +50,5 @@ export {
   mfcc,
   chroma,
   spectralFlux,
+  positiveFlux,
 };

src/main.ts

@@ -29,12 +29,14 @@ export interface MeydaFeaturesObject {
   rms: number;
   spectralCentroid: number;
   spectralFlatness: number;
+  spectralFlux: number;
   spectralKurtosis: number;
   spectralRolloff: number;
   spectralSkewness: number;
   spectralSlope: number;
   spectralSpread: number;
   zcr: number;
+  positiveFlux: number;
 }
 
 export type MeydaWindowingFunction =
@@ -63,7 +65,8 @@ export type MeydaAudioFeature =
   | "spectralSlope"
   | "spectralSpread"
   | "zcr"
-  | "buffer";
+  | "buffer"
+  | "positiveFlux";
 
 /**
  * A type representing an audio signal. In general it should be an array of

src/utilities.ts

@@ -93,13 +93,15 @@ export function mean(a) {
   );
 }
 
+const MEL_CONSTANT = 1127;
+
 function _melToFreq(melValue) {
-  var freqValue = 700 * (Math.exp(melValue / 1125) - 1);
+  var freqValue = 700 * (Math.exp(melValue / MEL_CONSTANT) - 1);
   return freqValue;
 }
 
 function _freqToMel(freqValue) {
-  var melValue = 1125 * Math.log(1 + freqValue / 700);
+  var melValue = MEL_CONSTANT * Math.log(1 + freqValue / 700);
   return melValue;
 }
 
@@ -270,3 +272,10 @@ export function frame(buffer, frameLength, hopLength) {
     .fill(0)
     .map((_, i) => buffer.slice(i * hopLength, i * hopLength + frameLength));
 }
+
+export function magnitudeForComplexSpectrum(complexSpectrum) {
+  return complexSpectrum.real.map((real, i) => {
+    const imag = complexSpectrum.imag[i];
+    return Math.sqrt(Math.pow(real, 2) + Math.pow(imag, 2));
+  });
+}