Java algorithm for normalizing audio

Question

I\'m trying to normalize an audio file of speech.

Specifically, where an audio file contains peaks in volume, I\'m trying to level it out, so the quiet sections are

Answer 1

I don't think the concept of "minimum sample value" is very meaningful, since the sample value just represents the current "height" of the sound wave at a certain time instant. I.e. its absolute value will vary between the peak value of the audio clip and zero. Thus, having a targetRangeMin seems to be wrong and will probably cause some distortion of the waveform.

I think a better approach might be to have some sort of weight function that decreases the sample value based on its size. I.e. bigger values are decreased by a large percentage than smaller values. This would also introduce some distortion, but probably not very noticeable.

Edit: here is a sample implementation of such a method:

public short normalize(short value) {
    short rawMax = // max from step1
    short targetMax = 8000;

    //This is the maximum volume reduction
    double maxReduce = 1 - targetMax/(double)rawMax;

    int abs = Math.abs(value);
    double factor = (maxReduce * abs/(double)rawMax);

    return (short) Math.round((1 - factor) * value); 
}

For reference, this is what your algorithm did to a sine curve with an amplitude of 10000:

This explains why the audio quality becomes much worse after being normalized.

This is the result after running with my suggested normalize method: