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CSS

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HTML 

              
                <div id="container"><canvas id="canvas"></canvas></div>
<audio id="audio" controls crossorigin></audio>
<input id="audioFileInput" type="file" accept="audio/*">
<script>
  function map(x, min, max, targetMin, targetMax) {
    return (x - min) / (max - min) * (targetMax - targetMin) + targetMin;
  }
  
  function clamp(x, min, max) {
    return Math.min(Math.max(x, min), max);
  }
  
  function idxWrapOver(x, length) {
    return (x % length + length) % length;
  }
  // Hz and FFT bin conversion
function hertzToFFTBin(x, y = 'round', bufferSize = 4096, sampleRate = 44100) {
  const bin = x * bufferSize / sampleRate;
  let func = y;
  
  if (!['floor','ceil','trunc'].includes(func))
    func = 'round'; // always use round if you specify an invalid/undefined value
  
  return Math[func](bin);
}

function fftBinToHertz(x, bufferSize = 4096, sampleRate = 44100) {
  return x * sampleRate / bufferSize;
}
  

// Calculate the FFT
function calcFFT(input) {
  let fft = input.map(x => x);
  let fft2 = input.map(x => x);
  transform(fft, fft2);
  let output = new Array(Math.round(fft.length/2)).fill(0);
  for (let i = 0; i < output.length; i++) {
    output[i] = Math.hypot(fft[i], fft2[i])/(fft.length);
  }
  return output;
}

function calcComplexFFT(input) {
  let fft = input.map(x => x);
  let fft2 = input.map(x => x);
  transform(fft, fft2);
  return input.map((_, i, arr) => {
    return {
      re: fft[i]/(arr.length/2),
      im: fft2[i]/(arr.length/2),
      magnitude: Math.hypot(fft[i], fft2[i])/(arr.length/2),
      phase: Math.atan2(fft2[i], fft[i])
    };
  });
}
  
  /**
 * FFT and convolution (JavaScript)
 * 
 * Copyright (c) 2017 Project Nayuki. (MIT License)
 * https://www.nayuki.io/page/free-small-fft-in-multiple-languages
 */

/* 
 * Computes the discrete Fourier transform (DFT) of the given complex vector, storing the result back into the vector.
 * The vector can have any length. This is a wrapper function.
 */
function transform(real, imag) {
	const n = real.length;
	if (n != imag.length)
		throw "Mismatched lengths";
	if (n <= 0)
		return;
	else if ((2 ** Math.trunc(Math.log2(n))) === n)  // Is power of 2
		transformRadix2(real, imag);
	else  // More complicated algorithm for arbitrary sizes
		transformBluestein(real, imag);
}


/* 
 * Computes the inverse discrete Fourier transform (IDFT) of the given complex vector, storing the result back into the vector.
 * The vector can have any length. This is a wrapper function. This transform does not perform scaling, so the inverse is not a true inverse.
 */
function inverseTransform(real, imag) {
	transform(imag, real);
}


/* 
 * Computes the discrete Fourier transform (DFT) of the given complex vector, storing the result back into the vector.
 * The vector's length must be a power of 2. Uses the Cooley-Tukey decimation-in-time radix-2 algorithm.
 */
function transformRadix2(real, imag) {
	// Length variables
	const n = real.length;
	if (n != imag.length)
		throw "Mismatched lengths";
	if (n <= 1)  // Trivial transform
		return;
	const logN = Math.log2(n);
	if ((2 ** Math.trunc(logN)) !== n)
		throw "Length is not a power of 2";
	
	// Trigonometric tables
	let cosTable = new Array(n / 2);
	let sinTable = new Array(n / 2);
	for (let i = 0; i < n / 2; i++) {
		cosTable[i] = Math.cos(2 * Math.PI * i / n);
		sinTable[i] = Math.sin(2 * Math.PI * i / n);
	}
	
	// Bit-reversed addressing permutation
	for (let i = 0; i < n; i++) {
		let j = reverseBits(i, logN);
		if (j > i) {
			let temp = real[i];
			real[i] = real[j];
			real[j] = temp;
			temp = imag[i];
			imag[i] = imag[j];
			imag[j] = temp;
		}
	}
	
	// Cooley-Tukey decimation-in-time radix-2 FFT
	for (let size = 2; size <= n; size *= 2) {
		let halfsize = size / 2;
		let tablestep = n / size;
		for (let i = 0; i < n; i += size) {
			for (let j = i, k = 0; j < i + halfsize; j++, k += tablestep) {
				const l = j + halfsize;
				const tpre =  real[l] * cosTable[k] + imag[l] * sinTable[k];
				const tpim = -real[l] * sinTable[k] + imag[l] * cosTable[k];
				real[l] = real[j] - tpre;
				imag[l] = imag[j] - tpim;
				real[j] += tpre;
				imag[j] += tpim;
			}
		}
	}
	
	// Returns the integer whose value is the reverse of the lowest 'bits' bits of the integer 'x'.
	function reverseBits(x, bits) {
		let y = 0;
		for (let i = 0; i < bits; i++) {
			y = (y << 1) | (x & 1);
			x >>>= 1;
		}
		return y;
	}
}


/* 
 * Computes the discrete Fourier transform (DFT) of the given complex vector, storing the result back into the vector.
 * The vector can have any length. This requires the convolution function, which in turn requires the radix-2 FFT function.
 * Uses Bluestein's chirp z-transform algorithm.
 */
function transformBluestein(real, imag) {
	// Find a power-of-2 convolution length m such that m >= n * 2 + 1
	const n = real.length;
	if (n != imag.length)
		throw "Mismatched lengths";
	const m = 2 ** Math.trunc(Math.log2(n*2)+1);
	
	// Trignometric tables
	let cosTable = new Array(n);
	let sinTable = new Array(n);
	for (let i = 0; i < n; i++) {
		let j = i * i % (n * 2);  // This is more accurate than j = i * i
		cosTable[i] = Math.cos(Math.PI * j / n);
		sinTable[i] = Math.sin(Math.PI * j / n);
	}
	
	// Temporary vectors and preprocessing
	let areal = newArrayOfZeros(m);
	let aimag = newArrayOfZeros(m);
	for (let i = 0; i < n; i++) {
		areal[i] =  real[i] * cosTable[i] + imag[i] * sinTable[i];
		aimag[i] = -real[i] * sinTable[i] + imag[i] * cosTable[i];
	}
	let breal = newArrayOfZeros(m);
	let bimag = newArrayOfZeros(m);
	breal[0] = cosTable[0];
	bimag[0] = sinTable[0];
	for (let i = 1; i < n; i++) {
		breal[i] = breal[m - i] = cosTable[i];
		bimag[i] = bimag[m - i] = sinTable[i];
	}
	
	// Convolution
	let creal = new Array(m);
	let cimag = new Array(m);
	convolveComplex(areal, aimag, breal, bimag, creal, cimag);
	
	// Postprocessing
	for (let i = 0; i < n; i++) {
		real[i] =  creal[i] * cosTable[i] + cimag[i] * sinTable[i];
		imag[i] = -creal[i] * sinTable[i] + cimag[i] * cosTable[i];
	}
}


/* 
 * Computes the circular convolution of the given real vectors. Each vector's length must be the same.
 */
function convolveReal(x, y, out) {
	const n = x.length;
	if (n != y.length || n != out.length)
		throw "Mismatched lengths";
	convolveComplex(x, newArrayOfZeros(n), y, newArrayOfZeros(n), out, newArrayOfZeros(n));
}


/* 
 * Computes the circular convolution of the given complex vectors. Each vector's length must be the same.
 */
function convolveComplex(xreal, ximag, yreal, yimag, outreal, outimag) {
	const n = xreal.length;
	if (n != ximag.length || n != yreal.length || n != yimag.length
			|| n != outreal.length || n != outimag.length)
		throw "Mismatched lengths";
	
	xreal = xreal.slice();
	ximag = ximag.slice();
	yreal = yreal.slice();
	yimag = yimag.slice();
	transform(xreal, ximag);
	transform(yreal, yimag);
	
	for (let i = 0; i < n; i++) {
		const temp = xreal[i] * yreal[i] - ximag[i] * yimag[i];
		ximag[i] = ximag[i] * yreal[i] + xreal[i] * yimag[i];
		xreal[i] = temp;
	}
	inverseTransform(xreal, ximag);
	
	for (let i = 0; i < n; i++) {  // Scaling (because this FFT implementation omits it)
		outreal[i] = xreal[i] / n;
		outimag[i] = ximag[i] / n;
	}
}


function newArrayOfZeros(n) {
	let result = new Array(n).fill(0);
	return result;
}
</script>
!

CSS 

              
                body {
  margin: 0;
  overflow: hidden;
}

audio {
  display: inline-block;
  width: 100%;
  height: 40px;
}

canvas {
  display: block;
  width: 100%;
}

#container {
  height: calc( 100vh - 40px );
}

#upload {
  display: none;
}
!

JS 

              
                const audioCtx = new AudioContext();
const audioPlayer = document.getElementById('audio');
const localAudioElement = document.getElementById('audioFileInput');
localAudioElement.addEventListener('change', loadLocalFile);
const canvas = document.getElementById('canvas'),
      ctx = canvas.getContext('2d'),
      container = document.getElementById('container');
const audioSource = audioCtx.createMediaElementSource(audioPlayer);
const analyser = audioCtx.createAnalyser();
analyser.fftSize = 32768; // maxes out FFT size
const dataArray = new Float32Array(analyser.fftSize);
const currentSpectrum = [],
      peaks = [],
      peakHolds = [],
      peakAccels = [];
const delay = audioCtx.createDelay();
audioSource.connect(delay);
delay.connect(audioCtx.destination);
//audioSource.connect(audioCtx.destination);
audioSource.connect(analyser);

const visualizerSettings = {
  type: 'fft',
  numBands: 96,
  fftSize: 4096,
  minFreq: 20,
  maxFreq: 20000,
  minNote: 4,
  maxNote: 124,
  noteTuning: 440,
  octaves: 12,
  detune: 0,
  bandwidth: 0.5,
  bandwidthOffset: 1,
  freqDist: 'octaves',
  fscale: 'logarithmic',
  windowFunction: 'hann',
  windowParameter: 1,
  windowSkew: 0,
  timeAlignment: 1,
  downsample: 0,
  granularDownsample: false,
  averageSamplesInstead: false,
  interpSize: 32,
  summationMode: 'max',
  useComplex: true,
  smoothInterp: true,
  smoothSlope: true,
  smoothingTimeConstant: 0,
  smoothingMode: 'avg',
  holdTime: 30,
  fallRate: 0.5,
  clampPeaks: true,
  peakMode: 'gravity',
  showPeaks: true,
  hzLinearFactor: 0,
  minDecibels: -90,
  maxDecibels: 0,
  useDecibels: true,
  gamma: 1,
  useAbsolute: true,
  freeze: false,
  color: 'none',
  showLabels: true,
  showLabelsY: true,
  amplitudeLabelInterval: 6,
  labelTuning: 440,
  showDC: true,
  showNyquist: true,
  mirrorLabels: true,
  diffLabels: false,
  labelMode : 'decade',
  barSpacing: 1,
  spacingMode: 'smooth',
  centerBars: false,
  peakHeight: 1,
  useLED: false,
  ledStrips: 128,
  darkMode: false,
  compensateDelay: false
},
      windowFunctionSettings = {
        'Rectangular': 'rectangular',
        'Triangular (Bartlett)': 'triangular',
        'Quadratic': 'quadratic spline',
        'Parzen': 'parzen',
        'Welch': 'welch',
        'Power of sine': 'power of sine',
        'Power of circle': 'circle',
        'Tukey (tapered cosine)': 'tukey',
        'Vorbis': 'vorbis',
        'Cascaded sine': 'cascaded sine',
        'Hann': 'hann',
        'Hamming': 'hamming',
        'Blackman': 'blackman',
        'Nuttall': 'nuttall',
        'Flat top': 'flattop',
        'Gaussian': 'gauss',
        'Hyperbolic cosine': 'cosh',
        'Kaiser': 'kaiser',
        'Poisson': 'exponential',
        'Hyperbolic secant': 'sech'
      },
      fscaleSettings = {
        'Bark': 'bark',
        'ERB': 'erb',
        'Cams': 'cam',
        'Mel (AIMP)': 'mel',
        'Linear': 'linear',
        'Logarithmic': 'logarithmic',
        'Hyperbolic sine': 'sinh',
        'Shifted logarithmic': 'shifted log',
        'Nth root': 'nth root',
        'Negative exponential': 'negative exponential',
        'Adjustable Bark': 'adjustable bark',
        'Period': 'period'
        },
      freqDistSettings = {
        'Octave bands': 'octaves',
        'Frequency bands': 'freqs',
        'Avee Player': 'avee'
      },
      typeSettings = {
        'FFT': 'fft',
        'CQT': 'cqt',
        'Filter bank energies': 'filterbank'
      },
      colorSettings = {
        'None': 'none',
        'Classic': 'classic',
        'Rainbow': 'rainbow',
        'Voice-Change-o-Matic': 'mdn',
        'foobar2000': 'fb2k',
        'foobar2000 (classic)': 'fb2k 2',
        'Prism': 'prism 2',
        'Prism (foo_musical_spectrum)': 'prism',
        'Prism (classic)': 'prism 3',
        'Audition': 'audition',
        'WMP Bars': 'wmp',
        'Ocean Mist': 'ocean',
        'Fire Storm': 'firestorm'
      },
      averagingOptions = {
        'Average': 'avg',
        'Peak': 'peak'
      },
      bandpowerAttributes = {
        'Maximum': 'max',
        'Minimum': 'min',
        'Average': 'avg',
        'RMS': 'rms',
        'Sum': 'sum',
        'RMS sum': 'rms sum',
        'Median': 'median'
      },
      labelModes = {
        'Decades': 'decade',
        'Octaves': 'octave',
        'Notes': 'note',
        'Automatic': 'auto'
      },
      peakModes = {
        'Classic': 'classic',
        'Gravity': 'gravity',
        'AIMP': 'aimp'
      },
      loader = {
        url: '',
        load: function() {
          audioPlayer.src = this.url;
          audioPlayer.play();
        },
        loadLocal: function() {
          localAudioElement.click();
        },
        toggleFullscreen: _ => {
          if (document.fullscreenElement === canvas)
            document.exitFullscreen();
          else
            canvas.requestFullscreen();
        }
      };

let gui = new dat.GUI();
gui.add(loader, 'url').name('URL');
gui.add(loader, 'load').name('Load');
gui.add(loader, 'loadLocal').name('Load from local device');
let settings = gui.addFolder('Visualization settings');
settings.add(visualizerSettings, 'type', typeSettings).name('Visualization algorithm');
settings.add(visualizerSettings, 'freqDist', freqDistSettings).name('Frequency band distribution');
// up to 192kHz sample rate is supported for full-range visualization
settings.add(visualizerSettings, 'minFreq', 0, 96000).name('Minimum frequency');
settings.add(visualizerSettings, 'maxFreq', 0, 96000).name('Maximum frequency');
settings.add(visualizerSettings, 'minNote', 0, 128).name('Minimum note');
settings.add(visualizerSettings, 'maxNote', 0, 128).name('Maximum note');
settings.add(visualizerSettings, 'noteTuning', 0, 96000).name('Octave bands tuning (nearest note = tuning frequency in Hz)');
settings.add(visualizerSettings, 'detune', -24, 24).name('Detune');
settings.add(visualizerSettings, 'fscale', fscaleSettings).name('Frequency scale');
settings.add(visualizerSettings, 'hzLinearFactor', 0, 100).name('Hz linear factor');
settings.add(visualizerSettings, 'numBands', 2, 1920, 1).name('Number of bands');
settings.add(visualizerSettings, 'octaves', 1, 192).name('Bands per octave');
settings.add(visualizerSettings, 'bandwidth', 0, 64).name('Bandwidth');
settings.add(visualizerSettings, 'bandwidthOffset', 0, 1).name('Transition smoothness');
settings.add(visualizerSettings, 'fftSize', 32, 32768, 1).name('Max time resolution (samples)');
settings.add(visualizerSettings, 'timeAlignment', -1, 1).name('CQT kernel time alignment');
settings.add(visualizerSettings, 'downsample', 0, 100).name('Downsample amount');
settings.add(visualizerSettings, 'granularDownsample').name('Unlock downsampling amount from power of two');
settings.add(visualizerSettings, 'averageSamplesInstead').name('Average samples instead of skipping for downsampled part of CQT');
settings.add(visualizerSettings, 'interpSize', 1, 64, 1).name('Lanczos interpolation kernel size');
settings.add(visualizerSettings, 'smoothInterp').name('Smoother bin interpolation on lower frequencies');
settings.add(visualizerSettings, 'useComplex').name('Use complex FFT coefficients as interpolation data');
settings.add(visualizerSettings, 'summationMode', bandpowerAttributes).name('Bandpower summation mode');
settings.add(visualizerSettings, 'smoothSlope').name('Smoother frequency slope on sum modes');
settings.add(visualizerSettings, 'windowFunction', windowFunctionSettings).name('Window function');
settings.add(visualizerSettings, 'windowParameter', 0, 10).name('Window parameter');
settings.add(visualizerSettings, 'windowSkew', -1, 1).name('Window skew');
settings.add(visualizerSettings, 'smoothingTimeConstant', 0, 100).name('Smoothing time constant');
settings.add(visualizerSettings, 'smoothingMode', averagingOptions).name('Time smoothing method');
settings.add(visualizerSettings, 'holdTime', 0, 120).name('Peak hold time');
settings.add(visualizerSettings, 'fallRate', 0, 2).name('Peak fall rate');
settings.add(visualizerSettings, 'peakMode', peakModes).name('Peak decay behavior');
settings.add(visualizerSettings, 'clampPeaks').name('Clamp peaks');
settings.add(visualizerSettings, 'useDecibels').name('Use logarithmic amplitude/decibel scale');
settings.add(visualizerSettings, 'useAbsolute').name('Use absolute value');
settings.add(visualizerSettings, 'gamma', 0.5, 10).name('Gamma');
settings.add(visualizerSettings, 'minDecibels', -120, 6).name('Lower amplitude range');
settings.add(visualizerSettings, 'maxDecibels', -120, 6).name('Higher amplitude range');
settings.add(visualizerSettings, 'freeze').name('Freeze analyser');
settings.add(visualizerSettings, 'showPeaks').name('Show peaks');
settings.add(visualizerSettings, 'peakHeight', 0.5, 32).name('Peak indicator height');
settings.add(visualizerSettings, 'color', colorSettings).name('Visualization color');
settings.add(visualizerSettings, 'showLabels').name('Show horizontal-axis labels');
settings.add(visualizerSettings, 'showLabelsY').name('Show vertical-axis labels');
settings.add(visualizerSettings, 'amplitudeLabelInterval', 0.5, 48).name('dB label interval');
settings.add(visualizerSettings, 'showDC').name('Show DC label');
settings.add(visualizerSettings, 'showNyquist').name('Show Nyquist frequency label');
settings.add(visualizerSettings, 'mirrorLabels').name('Mirror Y-axis labels');
settings.add(visualizerSettings, 'diffLabels').name('Use difference coloring for labels');
settings.add(visualizerSettings, 'labelMode', labelModes).name('Frequency label mode');
settings.add(visualizerSettings, 'labelTuning', 0, 96000).name('Note labels tuning (nearest note = tuning frequency in Hz)');
settings.add(visualizerSettings, 'barSpacing', 0, 1024).name('Bar spacing');
settings.add(visualizerSettings, 'spacingMode', ['rough', 'smooth', 'pixel perfect']).name('Bar spacing mode');
settings.add(visualizerSettings, 'centerBars').name('Center bars');
settings.add(visualizerSettings, 'useLED').name('Use LEDs');
settings.add(visualizerSettings, 'ledStrips', 2, 1080, 1).name('LED strip count');
settings.add(visualizerSettings, 'darkMode').name('Dark mode');
settings.add(visualizerSettings, 'compensateDelay').name('Compensate for delay');
gui.add(loader, 'toggleFullscreen').name('Toggle fullscreen mode');

function resizeCanvas() {
  const scale = devicePixelRatio,
        isFullscreen = document.fullscreenElement === canvas;
  canvas.width = (isFullscreen ? innerWidth : container.clientWidth)*scale;
  canvas.height = (isFullscreen ? innerHeight : container.clientHeight)*scale;
}

addEventListener('click', () => {
  if (audioCtx.state == 'suspended')
    audioCtx.resume();
});
addEventListener('resize', resizeCanvas);
resizeCanvas();

function loadLocalFile(event) {
  const file = event.target.files[0],
        reader = new FileReader();
  reader.onload = (e) => {
    audioPlayer.src = e.target.result;
    audioPlayer.play();
  };

  reader.readAsDataURL(file);
}
const test = map(0, 0, 1, -1, 1); // Smoke testing
visualize();
function visualize() {
  delay.delayTime.value = visualizerSettings.compensateDelay ? map(visualizerSettings.type === 'cqt' ? visualizerSettings.timeAlignment : -1, -1, 1, visualizerSettings.fftSize/audioCtx.sampleRate, 0) : 0;
  if (!visualizerSettings.freeze) {
    analyser.getFloatTimeDomainData(dataArray);
  }
  const fftData = new Array(visualizerSettings.fftSize),
        isNumerical = visualizerSettings.freqDist === 'avee',
        hzLinearFactor = visualizerSettings.hzLinearFactor/100,
        bandwidth = visualizerSettings.type === 'cqt' || visualizerSettings.type === 'filterbank' ? visualizerSettings.bandwidth : 0.5;
  let norm = 0;
  for (let i = 0; i < visualizerSettings.fftSize; i++) {
    const magnitude = dataArray[i+analyser.fftSize-visualizerSettings.fftSize],
          w = visualizerSettings.type === 'cqt' ? 2 : applyWindow(map(i, 0, visualizerSettings.fftSize, -1, 1), visualizerSettings.windowFunction, visualizerSettings.windowParameter, true, visualizerSettings.windowSkew);
    fftData[i] = magnitude * w;
    norm += w;
  }
  let freqBands = [];
  switch (visualizerSettings.freqDist) {
    case 'octaves':
      freqBands = generateOctaveBands(visualizerSettings.octaves, visualizerSettings.minNote, visualizerSettings.maxNote, visualizerSettings.detune, visualizerSettings.noteTuning, bandwidth);
      break;
    case 'avee':
      freqBands = generateAveePlayerFreqs(visualizerSettings.numBands, visualizerSettings.minFreq, visualizerSettings.maxFreq, hzLinearFactor, bandwidth);
      break;
    default:
    freqBands = generateFreqBands(visualizerSettings.numBands, visualizerSettings.minFreq, visualizerSettings.maxFreq, visualizerSettings.fscale, hzLinearFactor, bandwidth);
  }
  let spectrum;
  if (visualizerSettings.type === 'cqt')
    spectrum = cqt(fftData, freqBands, audioCtx.sampleRate, visualizerSettings.bandwidthOffset, visualizerSettings.timeAlignment, (x) => applyWindow(x, visualizerSettings.windowFunction, visualizerSettings.windowParameter, true, visualizerSettings.windowSkew), visualizerSettings.downsample/100, visualizerSettings.granularDownsample, visualizerSettings.averageSamplesInstead);
  else {
    const complexSpectrum = calcComplexFFT(fftData.map(x => x*fftData.length/norm/Math.SQRT2)),
          fullSpectrum = complexSpectrum.map(x => x.magnitude),
          useComplex = visualizerSettings.useComplex;
    if (visualizerSettings.type === 'filterbank')
      spectrum = calcFilterBankEnergies(freqBands, fullSpectrum, fftData.length, audioCtx.sampleRate);
    else
      spectrum = calcSpectrum(useComplex ? complexSpectrum : fullSpectrum, freqBands, visualizerSettings.interpSize, visualizerSettings.summationMode, useComplex, visualizerSettings.smoothInterp, visualizerSettings.smoothSlope, fftData.length, audioCtx.sampleRate);
    
  }
  const minLabelRange = Math.min(...freqBands.map(x => x.ctr)),
        maxLabelRange = Math.max(...freqBands.map(x => x.ctr)),
        bgColor = visualizerSettings.darkMode ? (visualizerSettings.color === 'fb2k' ? '#202020' : '#000') : '#fff',
        fgColor = visualizerSettings.darkMode ? (visualizerSettings.color === 'fb2k' ? '#c0c0c0' : '#fff') : '#000',
        ledStripHeight = Math.min(canvas.height / visualizerSettings.ledStrips, visualizerSettings.peakHeight);
  ctx.globalCompositeOperation = 'source-over';
  ctx.fillStyle = bgColor;
  ctx.strokeStyle = bgColor;
  ctx.fillRect(0, 0, canvas.width, canvas.height);
  let grad,
      peakColor = fgColor;
  switch (visualizerSettings.color) {
    case 'prism':
    case 'prism 2':
    case 'prism 3':
    case 'classic':
    case 'fb2k 2':
    case 'fb2k':
      grad = ctx.createLinearGradient(0, 0, 0, canvas.height);
      if (visualizerSettings.color === 'prism') {
        grad.addColorStop(0/5, '#fd0000');
        grad.addColorStop(1/5, '#ff8000');
        grad.addColorStop(2/5, '#ffff01');
        grad.addColorStop(3/5, '#7eff77');
        grad.addColorStop(4/5, '#0193a2');
        grad.addColorStop(5/5, '#002161');
        peakColor = grad;
      }
      else if (visualizerSettings.color === 'prism 2') {
        grad.addColorStop(0, '#a35');
        grad.addColorStop(1/9, '#c66');
        grad.addColorStop(2/9, '#e94');
        grad.addColorStop(3/9, '#ed0');
        grad.addColorStop(4/9, '#9d5');
        grad.addColorStop(5/9, '#4d8');
        grad.addColorStop(6/9, '#2cb');
        grad.addColorStop(7/9, '#0bc');
        grad.addColorStop(8/9, '#09c');
        grad.addColorStop(1, '#36b');
        peakColor = grad;
      }
      else if (visualizerSettings.color === 'prism 3') {
        grad.addColorStop(0, 'hsl(0, 100%, 50%)');
        grad.addColorStop(1/4, 'hsl(60, 100%, 50%)');
        grad.addColorStop(2/4, 'hsl(120, 100%, 50%)');
        grad.addColorStop(3/4, 'hsl(180, 100%, 50%)');
        grad.addColorStop(1, 'hsl(240, 100%, 50%)');
      }
      else if (visualizerSettings.color === 'classic') {
        grad.addColorStop(0, '#f00');
        grad.addColorStop(0.5, '#ff0');
        grad.addColorStop(1, '#0f0');
      }
      else if (visualizerSettings.color === 'fb2k 2') {
        grad.addColorStop(0, visualizerSettings.darkMode ? 'rgb(0, 128, 255)' : '#008');
        grad.addColorStop(1, visualizerSettings.darkMode ? '#fff' : '#000');
      }
      else {
        grad.addColorStop(0, visualizerSettings.darkMode ? '#569cd6' : 'rgb(0, 102, 204)');
        grad.addColorStop(1, visualizerSettings.darkMode ? '#c0c0c0' : '#000');
      }
      ctx.fillStyle = grad;
      break;
    case 'audition':
      peakColor = '#fafa1a';
      const highColor = '#f64646',
            midColor = '#f5d145',
            lowColor = '#36ed45',
            mindBColor = 10 ** (-30/20),
            maxdBColor = 10 ** (-12/20),
            startPoint = isNaN(ascale(mindBColor)) ? 0 : clamp(ascale(mindBColor), 0, 1),
            endPoint = isNaN(ascale(maxdBColor)) ? 0 : clamp(ascale(maxdBColor), 0, 1);
      grad = ctx.createLinearGradient(0, canvas.height, 0, 0);
      grad.addColorStop(0, lowColor);
      grad.addColorStop(startPoint, lowColor);
      grad.addColorStop(startPoint, midColor);
      grad.addColorStop(endPoint, midColor);
      grad.addColorStop(endPoint, highColor);
      ctx.fillStyle = grad;
      break;
    default:
      if (visualizerSettings.color === 'wmp') {
        grad = '#a7ed03';
        peakColor = '#e7f0ef';
      }
      else if (visualizerSettings.color === 'ocean') {
        grad = '#00f';
        peakColor = '#fff';
      }
      else if (visualizerSettings.color === 'firestorm') {
        grad = '#fea500';
        peakColor = '#f00';
      }
      ctx.fillStyle = fgColor;
  }
  ctx.strokeStyle = fgColor;
  currentSpectrum.length = spectrum.length;
  /*peaks.length = currentSpectrum.length;
  peakHolds.length = peaks.length;
  peakAccels.length = peaks.length;*/
  switch(visualizerSettings.smoothingMode) {
    case 'avg':
      calcSmoothingTimeConstant(currentSpectrum, spectrum, visualizerSettings.smoothingTimeConstant/100);
      break;
    case 'peak':
      calcPeakDecay(currentSpectrum, spectrum, visualizerSettings.smoothingTimeConstant/100);
      break;
    default:
      currentSpectrum = spectrum.map(x => Math.max(x));
  }
  calcDecay(currentSpectrum.map(ascale), peaks, peakHolds, peakAccels)
  currentSpectrum.map((x, i, arr) => {
    const frequencyInNotes = Math.log2(freqBands[i].ctr/visualizerSettings.labelTuning);
    switch(visualizerSettings.color) {
      case 'mdn':
        ctx.fillStyle = `rgb(${isNaN(ascale(x)) ? 0 : map(Math.max(Math.min(ascale(x), 1), 0), 0, 1, 0, 255)}, 50, 50)`;
        break;
      case 'rainbow':
        const color = `hsl(${isFinite(frequencyInNotes) ? frequencyInNotes * 360 : 0}, 100%, ${isFinite(frequencyInNotes) ? (50) : (visualizerSettings.darkMode * 100)}%)`;
        ctx.fillStyle = color;
        ctx.strokeStyle = color;
    }
    /*
    if (ascale(x) >= peaks[i] || isNaN(peaks[i]) || peaks[i] <= 0) {
      peaks[i] = ascale(x);
      peakHolds[i] = visualizerSettings.holdTime;
      peakAccels[i] = 0;
    }
    else if (peakHolds[i] > 0)
      peakHolds[i] -= 1;
    else {
      peakAccels[i] += visualizerSettings.fallRate / 256;
      peaks[i] -= peakAccels[i];
    }*/
    const pos = Math[visualizerSettings.spacingMode === 'smooth' ? 'max' : 'trunc'](i * canvas.width / arr.length) + Math.min(visualizerSettings.barSpacing, canvas.width / arr.length)/2 * visualizerSettings.centerBars,
          width = Math.max(1, (visualizerSettings.spacingMode === 'pixel perfect' ? Math.trunc((i+1) * canvas.width / arr.length)-Math.trunc(i * canvas.width / arr.length) : Math[visualizerSettings.spacingMode === 'smooth' ? 'max' : 'trunc'](canvas.width / arr.length))-visualizerSettings.barSpacing);
    
    ctx.fillStyle = grad !== undefined ? grad : ctx.fillStyle;
    if (visualizerSettings.useLED)
      ctx.fillRect(pos, canvas.height, width, map(Math.round(Math.max(ascale(x), 0)*visualizerSettings.ledStrips), 0, visualizerSettings.ledStrips, 0, -canvas.height));
    else
      ctx.fillRect(pos, canvas.height, width, map(Math.max(ascale(x), 0), 0, 1, 0, -canvas.height));
    ctx.fillStyle = peakColor;
    if (visualizerSettings.showPeaks) {
      if (visualizerSettings.useLED)
        ctx.fillRect(pos, Math.round(map(peaks[i], 0, 1, visualizerSettings.ledStrips, 0))*canvas.height/visualizerSettings.ledStrips, width, canvas.height/visualizerSettings.ledStrips);
      else
        ctx.fillRect(pos, map(peaks[i], 0, 1, canvas.height, 0), width, visualizerSettings.peakHeight);
    }
  });
  ctx.fillStyle = bgColor;
  if (visualizerSettings.useLED) {
    for (let i = 0; i < visualizerSettings.ledStrips; i++) {
      const size = canvas.height / visualizerSettings.ledStrips;
      ctx.fillRect(0, i * size, canvas.width, ledStripHeight);
    }
  }
  ctx.globalCompositeOperation = visualizerSettings.diffLabels ? 'difference' : 'source-over';
  ctx.fillStyle = visualizerSettings.diffLabels ? '#fff' : fgColor;
  ctx.strokeStyle = visualizerSettings.diffLabels ? '#fff' : fgColor;
  // label part
  ctx.font = `${Math.trunc(10*devicePixelRatio)}px sans-serif`;
  ctx.textAlign = 'start';
  // Frequency label part
  if (visualizerSettings.showLabels || visualizerSettings.showDC || visualizerSettings.showNyquist) {
    const labelScale = visualizerSettings.freqDist === 'octaves' ? 'log' : visualizerSettings.fscale;
    ctx.globalAlpha = 0.5;
    ctx.setLineDash([]);
    
    const freqLabels = [],
          isNote = visualizerSettings.labelMode === 'note',
          notes = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];

    let freqsTable;
    switch(visualizerSettings.labelMode) {
      case 'decade':
        freqsTable = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000];
        break;
      case 'octave':
        freqsTable = [31, 63.5, 125, 250, 500, 1000, 2000, 4000, 8000, 16000];
        break;
      case 'note':
        freqsTable = generateOctaveBands(12, 0, 132, 0, visualizerSettings.labelTuning).map(x => x.ctr);
        break;
      default:
        freqsTable = freqBands.map(x => x.ctr);
    }
    if (visualizerSettings.showLabels)
      freqLabels.push(...freqsTable);
    if (visualizerSettings.showDC)
      freqLabels.push(0);
    if (visualizerSettings.showNyquist)
      freqLabels.push(audioCtx.sampleRate/2);
    
    freqLabels.map(x => {
      const note = isFinite(Math.log2(x)) ? notes[idxWrapOver(Math.round(Math.log2(x)*12), notes.length)] : 'DC',
      isSharp = note.includes('#'),
      isC = note === 'C';
      
      ctx.globalAlpha = isNote ? (isSharp ? 0.2 : isC ? 0.8 : 0.5) : 0.5;
      const label = x === audioCtx.sampleRate/2 && visualizerSettings.showNyquist ? 'Nyquist' : isNote || x === 0 ? `${note}${isC ? Math.trunc(Math.log2(x)-4) : ''}` : (x >= 1000) ? `${x / 1000}kHz` : `${x}Hz`,
            posX = isNumerical ? getLabelPosFromFreqBands(freqBands, x)*canvas.width/freqBands.length : map(fscale(x, labelScale, visualizerSettings.hzLinearFactor/100), fscale(minLabelRange, labelScale, visualizerSettings.hzLinearFactor/100), fscale(maxLabelRange, labelScale, visualizerSettings.hzLinearFactor/100), canvas.width/spectrum.length/2, canvas.width - canvas.width/spectrum.length/2);
      ctx.beginPath();
      ctx.lineTo(posX, canvas.height);
      ctx.lineTo(posX, 0);
      ctx.stroke();
      ctx.globalAlpha = 1;
      ctx.fillText(label, posX, canvas.height);
    });
    ctx.setLineDash([]);
    ctx.globalAlpha = 1;
    ctx.textAlign = 'start';
  }
  // Amplitude/decibel label part
  if (visualizerSettings.showLabelsY) {
    const dBLabelData = [-Infinity],
          mindB = Math.min(visualizerSettings.minDecibels, visualizerSettings.maxDecibels),
          maxdB = Math.max(visualizerSettings.minDecibels, visualizerSettings.maxDecibels),
          minLabelIdx = Math.round(mindB/visualizerSettings.amplitudeLabelInterval),
          maxLabelIdx = Math.round(maxdB/visualizerSettings.amplitudeLabelInterval);
    
    if (isFinite(minLabelIdx) && isFinite(maxLabelIdx)) {
      for (let i = maxLabelIdx; i >= minLabelIdx; i--) {
        dBLabelData.push(i*visualizerSettings.amplitudeLabelInterval);
      }
    }
    
    ctx.globalAlpha = 0.5;
    ctx.setLineDash([]);
    dBLabelData.map(x => {
      ctx.globalAlpha = 0.5;
      const label = `${x}dB`,
            posY = map(ascale(10 ** (x/20)), 0, 1, canvas.height, 0);
      ctx.beginPath();
      ctx.lineTo(0, posY);
      ctx.lineTo(canvas.width, posY);
      ctx.stroke();
      ctx.globalAlpha = 1;
      ctx.textAlign = visualizerSettings.mirrorLabels ? 'end' : 'start'
      ctx.fillText(label, canvas.width * visualizerSettings.mirrorLabels, posY);
    });
    ctx.setLineDash([]);
    ctx.globalAlpha = 1;
    ctx.textAlign = 'start'
  }
  requestAnimationFrame(visualize);
}

function applyWindow(posX, windowType = 'Hann', windowParameter = 1, truncate = true, windowSkew = 0) {
  let x = windowSkew > 0 ? ((posX/2-0.5)/(1-(posX/2-0.5)*10*(windowSkew ** 2)))/(1/(1+10*(windowSkew ** 2)))*2+1 :
                           ((posX/2+0.5)/(1+(posX/2+0.5)*10*(windowSkew ** 2)))/(1/(1+10*(windowSkew ** 2)))*2-1;
  
  if (truncate && Math.abs(x) > 1)
    return 0;
  
  switch (windowType.toLowerCase()) {
    default:
      return 1;
    case 'hanning':
    case 'cosine squared':
    case 'hann':
      return Math.cos(x*Math.PI/2) ** 2;
    case 'raised cosine':
    case 'hamming':
      return 0.54 + 0.46 * Math.cos(x*Math.PI);
    case 'power of sine':
      return Math.cos(x*Math.PI/2) ** windowParameter;
    case 'circle':
    case 'power of circle':
      return Math.sqrt(1 - (x ** 2)) ** windowParameter;
    case 'tapered cosine':
    case 'tukey':
      return Math.abs(x) <= 1-windowParameter ? 1 : 
      (x > 0 ? 
       (-Math.sin((x-1)*Math.PI/windowParameter/2)) ** 2 :
       Math.sin((x+1)*Math.PI/windowParameter/2) ** 2);
    case 'blackman':
      return 0.42 + 0.5 * Math.cos(x*Math.PI) + 0.08 * Math.cos(x*Math.PI*2);
    case 'nuttall':
      return 0.355768 + 0.487396 * Math.cos(x*Math.PI) + 0.144232 * Math.cos(2*x*Math.PI) + 0.012604 * Math.cos(3*x*Math.PI);
    case 'flat top':
    case 'flattop':
      return 0.21557895 + 0.41663158 * Math.cos(x*Math.PI) + 0.277263158 * Math.cos(2*x*Math.PI) + 0.083578947 * Math.cos(3*x*Math.PI) + 0.006947368 * Math.cos(4*x*Math.PI);
    case 'kaiser':
      return Math.cosh(Math.sqrt(1-(x ** 2))*(windowParameter ** 2))/Math.cosh(windowParameter ** 2);
    case 'gauss':
    case 'gaussian':
      return Math.exp(-(windowParameter ** 2)*(x ** 2));
    case 'cosh':
    case 'hyperbolic cosine':
      return Math.E ** (-(windowParameter ** 2)*(Math.cosh(x)-1));
    case 'bartlett':
    case 'triangle':
    case 'triangular':
      return 1 - Math.abs(x);
    case 'poisson':
    case 'exponential':
      return Math.exp(-Math.abs(x * (windowParameter ** 2)));
    case 'hyperbolic secant':
    case 'sech':
      return 1/Math.cosh(x * (windowParameter ** 2));
    case 'quadratic spline':
      return Math.abs(x) <= 0.5 ? -((x*Math.sqrt(2)) ** 2)+1 : (Math.abs(x*Math.sqrt(2))-Math.sqrt(2)) ** 2;
    case 'parzen':
      return Math.abs(x) > 0.5 ? -2 * ((-1 + Math.abs(x)) ** 3) : 1 - 24 * (Math.abs(x/2) ** 2) + 48 * (Math.abs(x/2) ** 3);
    case 'welch':
      return 1 - (x ** 2);
    case 'ogg':
    case 'vorbis':
      return Math.sin(Math.PI/2 * Math.cos(x*Math.PI/2) ** 2);
    case 'cascaded sine':
    case 'cascaded cosine':
    case 'cascaded sin':
    case 'cascaded cos':
      return 1 - Math.sin(Math.PI/2 * Math.sin(x*Math.PI/2) ** 2);
  }
}

function fscale(x, freqScale = 'logarithmic', freqSkew = 0.5) {
  switch(freqScale.toLowerCase()) {
    default:
      return x;
    case 'log':
    case 'logarithmic':
      return Math.log2(x);
    case 'mel':
      return Math.log2(1+x/700);
    case 'critical bands':
    case 'bark':
      return (26.81*x)/(1960+x)-0.53;
    case 'equivalent rectangular bandwidth':
    case 'erb':
      return Math.log2(1+0.00437*x);
    case 'cam':
    case 'cams':
      return Math.log2((x/1000+0.312)/(x/1000+14.675));
    case 'sinh':
    case 'arcsinh':
    case 'asinh':
      return Math.asinh(x/(10 ** (freqSkew*4)));
    case 'shifted log':
    case 'shifted logarithmic':
      return Math.log2((10 ** (freqSkew*4))+x);
    case 'nth root':
      return x ** (1/(11-freqSkew*10));
    case 'negative exponential':
      return -(2 ** (-x/(2 ** (7+freqSkew*8))));
    case 'adjustable bark':
      return (26.81 * x)/((10 ** (freqSkew*4)) + x);
    case 'period':
      return 1/x;
  }
}

function invFscale(x, freqScale = 'logarithmic', freqSkew = 0.5) {
  switch(freqScale.toLowerCase()) {
    default:
      return x;
    case 'log':
    case 'logarithmic':
      return 2 ** x;
    case 'mel':
      return 700 * ((2 ** x) - 1);
    case 'critical bands':
    case 'bark':
      return 1960 / (26.81/(x+0.53)-1);
    case 'equivalent rectangular bandwidth':
    case 'erb':
      return (1/0.00437) * ((2 ** x) - 1);
    case 'cam':
    case 'cams':
      return (14.675 * (2 ** x) - 0.312)/(1-(2 ** x)) * 1000;
    case 'sinh':
    case 'arcsinh':
    case 'asinh':
      return Math.sinh(x)*(10 ** (freqSkew*4));
    case 'shifted log':
    case 'shifted logarithmic':
      return (2 ** x) - (10 ** (freqSkew*4));
    case 'nth root':
      return x ** ((11-freqSkew*10));
    case 'negative exponential':
      return -Math.log2(-x)*(2 ** (7+freqSkew*8));
    case 'adjustable bark':
      return (10 ** (freqSkew*4)) / (26.81 / x - 1);
    case 'period':
      return 1/x;
  }
}
function ascale(x) {
  if (visualizerSettings.useDecibels)
    return map(20*Math.log10(x), visualizerSettings.minDecibels, visualizerSettings.maxDecibels, 0, 1);
  else
    return map(x ** (1/visualizerSettings.gamma), !visualizerSettings.useAbsolute * (10 ** (visualizerSettings.minDecibels/20)) ** (1/visualizerSettings.gamma), (10 ** (visualizerSettings.maxDecibels/20)) ** (1/visualizerSettings.gamma), 0, 1);
}

/**
 * Constant-Q Transform (CQT) calculated using Goertzel algorithm
 *
 * This by itself doesn't need Web Audio API in order to work but it is necessary for real-time visualizations
 *
 * Real-time usage:
 * analyserNode.getFloatTimeDomainData(dataArray);
 * const spectrum = cqt(dataArray, freqBands, audioCtx.sampleRate, bandwidthOffset, windowFunction);
 *
 * Note: the implementation of this CQT is slow compared to FFT
 */

function cqt(waveform, hzArray = generateOctaveBands(), sampleRate = 44100, bandwidthOffset = 1, alignment = 1, windowFunction = applyWindow, downsample = 0, granularDownsample = false, averageSamplesInstead = false) {
  return hzArray.map(x => {
    const bandwidth = Math.abs(x.hi - x.lo) + (sampleRate/waveform.length) * bandwidthOffset,
          tlen = Math.min(1/bandwidth, waveform.length/sampleRate),
          granularDownsampleAmount = Math.max(1, Math.trunc((sampleRate*downsample) / (x.ctr + tlen))),
          downsampleAmount = granularDownsample ? granularDownsampleAmount : 2 ** Math.trunc(Math.log2(granularDownsampleAmount));
    const coeff = 2 * Math.cos(2*Math.PI*x.ctr/sampleRate*downsampleAmount);
    let f1 = 0,
        f2 = 0,
        sine,
        offset = Math.trunc((waveform.length-tlen*sampleRate)*(0.5+alignment/2)),
        lowerIdx = offset,
        higherIdx = Math.trunc(tlen*sampleRate)+offset-1,
        norm = 0;
    for (let i = Math.trunc(lowerIdx/downsampleAmount); i <= Math.trunc(higherIdx/downsampleAmount); i++) {
      let data = 0;
      if (averageSamplesInstead && isFinite(downsampleAmount)) {
        for (let j = 0; j < downsampleAmount; j++) {
          data += (i*downsampleAmount+j) < waveform.length ? waveform[i*downsampleAmount+j] : 0;
        }
        data /= downsampleAmount;
      }
      else {
        data = waveform[i*downsampleAmount];
      }
      let posX = (i*downsampleAmount - lowerIdx) / (higherIdx - lowerIdx) * 2 - 1;
      let w = windowFunction(posX);
      norm += w;
      
      // Goertzel transform
      sine = data*w + coeff * f1 - f2;
      f2 = f1;
      f1 = sine;
    }
    return Math.sqrt(f1 ** 2 + f2 ** 2 - coeff * f1 * f2) / norm;
  });
}

function generateFreqBands(N = 128, low = 20, high = 20000, freqScale, freqSkew, bandwidth = 0.5) {
  let freqArray = [];
  for (let i = 0; i < N; i++) {
    freqArray.push({
      lo: invFscale( map(i-bandwidth, 0, N-1, fscale(low, freqScale, freqSkew), fscale(high, freqScale, freqSkew)), freqScale, freqSkew),
      ctr: invFscale( map(i, 0, N-1, fscale(low, freqScale, freqSkew), fscale(high, freqScale, freqSkew)), freqScale, freqSkew),
      hi: invFscale( map(i+bandwidth, 0, N-1, fscale(low, freqScale, freqSkew), fscale(high, freqScale, freqSkew)), freqScale, freqSkew)
    });
  }
  return freqArray;
}

function generateOctaveBands(bandsPerOctave = 12, lowerNote = 4, higherNote = 123, detune = 0, tuningFreq = 440, bandwidth = 0.5) {
  const tuningNote = isFinite(Math.log2(tuningFreq)) ? Math.round((Math.log2(tuningFreq)-4)*12)*2 : 0,
        root24 = 2 ** ( 1 / 24 ),
        c0 = tuningFreq * root24 ** -tuningNote, // ~16.35 Hz
        groupNotes = 24/bandsPerOctave;
  let bands = [];
  for (let i = Math.round(lowerNote*2/groupNotes); i <= Math.round(higherNote*2/groupNotes); i++) {
    bands.push({
      lo: c0 * root24 ** ((i-bandwidth)*groupNotes+detune),
      ctr: c0 * root24 ** (i*groupNotes+detune),
      hi: c0 * root24 ** ((i+bandwidth)*groupNotes+detune)
    });
  }
  return bands;
}

// Calculate band frequencies, method derived from Avee Player
function generateAveePlayerFreqs(N, minFreq = 20, maxFreq = 20000, hzLinearFactor = 0, bandwidth = 0.5) {
  const freqBands = [];
  for (let i = 0; i < N; i++) {
    freqBands[i] = {
      lo: logSpace(minFreq, maxFreq, i-bandwidth, N-1, hzLinearFactor),
      ctr: logSpace(minFreq, maxFreq, i, N-1, hzLinearFactor),
      hi: logSpace(minFreq, maxFreq, i+bandwidth, N-1, hzLinearFactor),
      lowerBound: logSpace(minFreq, maxFreq, i-0.5, N-1, hzLinearFactor),
      higherBound: logSpace(minFreq, maxFreq, i+0.5, N-1, hzLinearFactor)
    };
  }
  return freqBands;
}

function logSpace(x, y, z, w, l) {
  const centerFreq = x * ((y/x) ** (z/w));
  return centerFreq * (1-l) + (x + ((y - x) * z * (1/w))) * l;
}

// needed for positioning Hz labels and ticks correctly where frequency band values are derived numerically rather than from closed-form frequency scale equations
function getLabelPosFromFreqBands(freqBands, x) {
  let idx = 0;
  if (x <= freqBands[0].lowerBound || x >= freqBands[freqBands.length-1].higherBound) {
    idx = (freqBands.length-1) * (x >= freqBands[freqBands.length-1].higherBound);
  }
  else {
    for (let i = 0; i < freqBands.length; i++) {
      if ((x >= freqBands[i].lowerBound && x <= freqBands[i].higherBound)) {
        idx = i;
        break;
      }
    }
  }
  return map(x, freqBands[idx].lowerBound, freqBands[idx].higherBound, idx, idx+1);
}

// Calculates bandpower from FFT (foobar2000 flavored, can be enhanced by using complex FFT coefficients instead of magnitude-only FFT data)
function calcSpectrum(fftCoeffs, freqBands, interpSize = 4, summationMode = 'max', useComplex = false, smoothInterp = true, smoothGainTransition = true, bufferSize = 4410, sampleRate = 44100) {
  return freqBands.map(x => {
    const minIdx = hertzToFFTBin(Math.min(x.hi, x.lo), 'ceil', bufferSize, sampleRate),
          maxIdx = hertzToFFTBin(Math.max(x.hi, x.lo), 'floor', bufferSize, sampleRate),
          minIdx2 = smoothInterp ? hertzToFFTBin(Math.min(x.hi, x.lo), 'round', bufferSize, sampleRate) + 1 : minIdx,
          maxIdx2 = smoothInterp ? hertzToFFTBin(Math.max(x.hi, x.lo), 'round', bufferSize, sampleRate) - 1 : maxIdx,
          bandGain = smoothGainTransition && (summationMode === 'sum' || summationMode === 'rms sum') ? Math.hypot(1, ((x.hi - x.lo) * bufferSize / sampleRate) ** (1-(summationMode === 'rms' || summationMode === 'rms sum')/2)) : 1;
    
    if (minIdx2 > maxIdx2)
      return Math.abs(lanzcos(fftCoeffs, x.ctr * bufferSize / sampleRate, interpSize, useComplex)) * bandGain;
    else {
      let sum = summationMode === 'min' ? Infinity : 0,
          diff = 0;
      const overflowCompensation = Math.max(maxIdx - minIdx - bufferSize, 0),
            isAverage = (summationMode === 'avg' || summationMode === 'rms') || ((summationMode === 'sum' || summationMode === 'rms sum') && smoothGainTransition),
            isRMS = summationMode === 'rms' || summationMode === 'rms sum',
            isMedian = summationMode === 'median',
            medianData = [];
      for (let i = minIdx; i <= maxIdx - overflowCompensation; i++) {
        const binIdx = (i % fftCoeffs.length + fftCoeffs.length) % fftCoeffs.length,
              data = useComplex ? fftCoeffs[binIdx].magnitude : fftCoeffs[binIdx];
        switch(summationMode) {
          case 'max':
            sum = Math.max(data, sum)
            break;
          case 'min':
            sum = Math.min(data, sum);
            break;
          case 'avg':
          case 'rms':
          case 'sum':
          case 'rms sum':
            sum += data ** (1 + isRMS);
            break;
          case 'median':
            medianData.push(data);
            break;
          default:
            sum = data;
        }
        diff++;
      }
      if (isMedian)
        sum = median(medianData);
      else
        sum /= isAverage ? diff : 1;
      return (isRMS ? Math.sqrt(sum) : sum) * bandGain;
    }
  });
}

// Calculates spectrum based on Mel (or actually arbitrary frequency) filter bank energies
function calcFilterBankEnergies(freqBands, fftData, bufferSize = 4096, sampleRate = 44100) {
  return freqBands.map(x => {
    let sum = 0,
        minBin = Math.min(x.lo, x.hi) * bufferSize / sampleRate,
        midBin = x.ctr * bufferSize / sampleRate,
        maxBin = Math.max(x.lo, x.hi) * bufferSize / sampleRate,
        overflowCompensation = Math.max(0, maxBin-minBin-bufferSize);
    for (let i = Math.floor(midBin); i >= Math.floor(minBin+overflowCompensation); i--) {
      sum += (fftData[idxWrapOver(i, fftData.length)] * Math.max(map(i, minBin, midBin, 0, 1), 0)) ** 2;
    }
    for (let i = Math.ceil(midBin); i <= Math.ceil(maxBin-overflowCompensation); i++) {
      sum += (fftData[idxWrapOver(i, fftData.length)] * Math.max(map(i, maxBin, midBin, 0, 1), 0)) ** 2;
    }
    return Math.sqrt(sum);
  });
}

function lanzcos(data, x, kernelSize = 4, inSpectrum = false) {
  let sum = 0,
      complexSum = {
        re: 0,
        im: 0
      };
  for (let i = -kernelSize + 1; i <= kernelSize; i++) {
    const pos = Math.floor(x)+i,//i+x,
          twiddle = x-pos,//-pos+Math.round(pos)+i,
          w = Math.abs(twiddle) <= 0 ? 1 : Math.sin(twiddle*Math.PI)/(twiddle*Math.PI) * Math.sin(Math.PI*twiddle/kernelSize)/(Math.PI*twiddle/kernelSize),
          idx = (pos % data.length + data.length) % data.length;
    if (inSpectrum) {
      complexSum.re += data[idx].re * w * (-1 + (i % 2 + 2) % 2 * 2);
      complexSum.im += data[idx].im * w * (-1 + (i % 2 + 2) % 2 * 2);
    }
    else
      sum += data[idx] * w;
  }
  if (inSpectrum)
    return Math.hypot(complexSum.re, complexSum.im);
  else
    return sum;
}

function calcSmoothingTimeConstant(targetArr, sourceArr, factor = 0.5) {
  for (let i = 0; i < targetArr.length; i++) {
    targetArr[i] = (isNaN(targetArr[i]) ? 0 : targetArr[i])*(factor)+(isNaN(sourceArr[i]) ? 0 : sourceArr[i])*(1-factor);
  }
}

function calcPeakDecay(targetArr, sourceArr, factor = 0.5) {
  for (let i = 0; i < targetArr.length; i++) {
    targetArr[i] = Math.max(isNaN(targetArr[i]) ? 0 : targetArr[i] * factor, isNaN(sourceArr[i]) ? 0 : sourceArr[i]);
  }
}

function median(data) {
  if (!data.length)
    return NaN;
  else if (data.length <= 1)
    return data[0];
  
  const sortedData = data.slice().sort((x, y) => x-y),
        half = Math.trunc(data.length/2);
  
  if (data.length % 2)
    return sortedData[half];
  
  return (sortedData[half-1] + sortedData[half]) / 2;
}

// Peak decay calculation
function calcDecay(source, p, h, a) {
  p.length = source.length;
  h.length = p.length;
  a.length = p.length;
  for (let i = 0; i < p.length; i++) {
    p[i] = isFinite(p[i]) ? p[i] : 0;
    if (source[i] >= p[i]) {
      h[i] = visualizerSettings.peakMode === 'aimp' ? (isFinite(h[i]) ? h[i] : 0) + ((visualizerSettings.clampPeaks ? Math.max(Math.min(source[i], 1), 0) : source[i]) - p[i]) * visualizerSettings.holdTime : visualizerSettings.holdTime;
      p[i] = source[i];
      a[i] = 0;
    }
    else if (h[i] >= 0) {
      if (visualizerSettings.peakMode === 'aimp')
        p[i] += (h[i] - Math.max(h[i]-1, 0))/visualizerSettings.holdTime;
      h[i] -= 1;
      h[i] = Math.min(h[i], visualizerSettings.holdTime/(visualizerSettings.peakMode !== 'aimp'));
    }
    else {
      switch (visualizerSettings.peakMode) {
        case 'gravity':
          a[i] += visualizerSettings.fallRate / 256;
          break;
        case 'aimp':
          a[i] = visualizerSettings.fallRate / 256 * ((p[i] < 0.5)+1);
          break;
        default:
          a[i] = visualizerSettings.fallRate / 256
      }
      p[i] -= a[i];
    }
    p[i] = visualizerSettings.clampPeaks ? Math.max(Math.min(p[i], 1), 0) : p[i];
  }
}
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