How does the normalization of an mp3 work?
The normalization of the loudness of an mp3 is based on perception.
The human ear has its peculiarities and the study of these have allowed the development of the normalization algorithm for mp3 files.
Initially what was needed was simply to reduce the space an audio file took up, while maintaining high quality.
We must remember that in the early years of the internet, it was very slow and hard drives had very little capacity. What made it impossible to download a wav file (this option is still not used today), which is the one with the “original” quality because the wav takes up a lot of space.
So the normalization algorithm of an mp3 was based on being able to understand how the human ear works to be able to discard information without sacrificing quality, based on the way we perceive music and thus, the mp3 file, which occupies much less space ( a tenth of the original) sounds almost the same as the original.
But… what information can be discarded without the human ear noticing? How is it achieved that even discarding information, an mp3 sounds almost the same as the original?
The first thing is to discard all the sounds that are not perceived by the human ear, but are nevertheless present in the original music wav file. Because the human ear can only perceive sounds in a range of frequencies, any lower frequency will not be heard and any higher frequency will not be heard either. So it’s safe to rule out silences, and also to rule out low and high frequencies that are beyond our ability to perceive.
But there are other phenomena in human hatred, such as the so-called masking. It happens that if we listen to a frequency at high volume and immediately after (or even at the same time) we listen to another instrument or sound with a similar frequency, our ear will not perceive this second sound… Then it is also possible to discard these sounds that are masked by first. Almost all frequency redundancy can be discarded without the human ear being able to perceive it.
So if we take a wav file and remove all the frequencies that are outside of our hearing range and also the masking, we will have been able to reduce the new audio considerably. If we also add a compression (like the one used for a .zip file), we will have a reduction so great that the new file will weigh one tenth of the original.
This allows the new file to be much more manageable than the original and to take up much less space on the hard drive, which was of crucial importance in those years.
This method that we are explaining in general was the one that was used two decades ago or more. Today Mp4Gain uses much more modern and complex methods, which provide more surprising results.
In addition, Mp4Gain is capable of normalizing not only mp3 files, but all popular audio formats and it can also normalize videos. And this is based on more modern, efficient and state-of-the-art algorithms, which provides a much better result.
Generally speaking, we have provided a non-technical explanation of how audio files were compressed to make an mp3.
We advise you to download Mp4Gain and check its quality for yourself. You guys are going to love it.
