Decibel value in web audio

Question

I'm using cordova-plugin-audioinput plugin for a JavaScript app that I'm developing. I'm trying to get the different decibel values at different frequencies in realtime using this code:

function startCapture() {
    audioinput.start({
        audioSourceType: 9,
        sampleRate: 44100,
        streamToWebAudio: true
    });

    audioCtx = audioinput.getAudioContext();
    analyser = audioCtx.createAnalyser();
    analyser.fftSize = 8192;
    analyser.maxDecibels = 0;
    audioinput.connect(analyser)

    bufferLength = analyser.frequencyBinCount;
    dataArray = new Uint8Array(bufferLength);
}

The data gets saved into the dataArray using analyser.getByteFrequencyData(dataArray);

Even though I specify maxDecibels to 0, the dataArray gets filled with positive values which doesn't really make any sense to me. I need the end result to be in decibels and even though the values that get pushed into dataArray react accordingly to the volume in realtime, they're not in decibels.

You don't show how `dataArray` is filled. I'm going to guess that you're using `getByteFrequencyData`. Is that so? — Raymond Toy, Jul 11 '18 at 22:33

score 1 · Answer 1 · answered Jul 12 '18 at 14:33

1

The values returned by getByteFrequencyData() are always in the range from 0 to 255. And these values are mapped linearly from minDecibels to maxDecibels. See the getByteFrequencyData.

answered Jul 12 '18 at 14:33

Raymond Toy

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Decibel value in web audio

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