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FIX: Prevent misalignment of [Spectrogram] at start and end of sample. #3904

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FIX: Prevent misalignment of [Spectrogram] at start and end of sample. #3904

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27 changes: 27 additions & 0 deletions src/plugins/spectrogram.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -592,6 +592,9 @@ class SpectrogramPlugin extends BasePlugin<SpectrogramPluginEvents, SpectrogramP
const channelFreq = []
let currentOffset = 0

channelFreq.push(new Uint8Array(fftSamples / 2).fill(0))
channelFreq.push(new Uint8Array(fftSamples / 2).fill(0))

while (currentOffset + fftSamples < channelData.length) {
const segment = channelData.slice(currentOffset, currentOffset + fftSamples)
const array = new Uint8Array(fftSamples / 2)
Expand All @@ -615,6 +618,30 @@ class SpectrogramPlugin extends BasePlugin<SpectrogramPluginEvents, SpectrogramP

currentOffset += fftSamples - noverlap
}

// Add 0 padding to the end of the audio if some data was left out due to window mismatch
if( channelData.length - currentOffset != 0) {
const segment = new Float32Array(fftSamples)
segment.set(channelData.slice(currentOffset, channelData.length))
const array = new Uint8Array(fftSamples / 2).fill(0)
let spectrum = fft.calculateSpectrum(segment);
if (this.scale == 'mel') {
spectrum = this.applyMelFilterBank(spectrum, melFilterBank);
}
for (let j = 0; j < fftSamples / 2; j++) {
// Based on: https://manual.audacityteam.org
let valueDB = 20 * Math.log10(spectrum[j])
if (valueDB < -this.rangeDB) {
array[j] = 0
} else if (valueDB > -this.gainDB) {
array[j] = 255
} else {
array[j] = (valueDB + this.gainDB) / this.rangeDB * 255 + 256
}
}
channelFreq.push(array)
}

frequencies.push(channelFreq)
// frequencies: [channel, sample, freq]
}
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