Incidentally, I prefer to normalise to 98% (although I won't adjust anything over 92%).

If you imagine the waveform as a vertical graph of the speaker's position over time, the speaker does not actually follow that graph. The speaker cone has mass, and thus inertia, which means that sudden acceleration and deceleration still takes time. To me, this means that a speaker will slightly overshoot the mark as you come up to the top or bottom of a big impulse (e.g. bass drum hit) and will move beyond where it is being told to by the electricity flowing through its coil. To me this says that normalising at 98% will give you a little bit of headroom for the speaker to move.

But, as I've realised in typing this note, this argument is false for two reasons. Fundamentally the thing that controls how far your speaker is actually going is not so much the waveform as the amount of amplification. You could wipe out a speaker on a waveform normalised to 50% simply by amplifying it by 150% of the speaker's capability. What normalisation gives you is [u]headroom[/u] - the ability to hear soft sounds above the noise floor of your system. So normalising to 100% doesn't affect anything.

I will argue that normalising less than five percent involves you in integer rounding problems that will introduce digital noise. For example, if you've got a value of 31111, and you're supposed to amplify it by 5%, then you're multiplying by 1.05. This gives you a value of 32666.55, which you would then have to round to 32667 because you're working with 16-bit signed integers. This rounding means you're introducing a slight error in your values, which will show up as noise (because it's essentially bit 'jitter').

But then, a rough top-of-brain calculation says that this will be showing up at -92db, which is almost too soft for the human ear to hear (the blood running through your ears makes more noise, I'd bet).

So much for that idea. Still, the old saying of 'if it ain't broke, don't fix it' has something in it. Since normalisation introduces noise, you're better off only using it when you will get a tangible benefit (better usage of your bandwidth).

Have fun,

Paul

Save the whales. Feed the hungry. Free the mallocs.