When you normalize a track, it moves all the audio samples in the file up by the same amount, so that the highest sample value is at or near the maximum allowed (0 dB) (or the level you specify). If your peak sample is already near that, then there won't be any noticeable increase in volume. If the peak sample started at -6 dB, and you normalized to 0 dB, then you'd get a 6 dB gain in volume that would be noticeable.

If you were going to get a file professionally mastered, they want the peaks at around -3 dB, not at the maximum.

Ralph
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