Managing Volume: ReplayGain(RG) / MP3Gain / Sound Check (iTunes)

ReplayGain(RG), MP3Gain, Sound Check (iTunes)
These features are used to normalize the audio files, I mean music files.
I’m gonna sum up the data I’ve collected, thereby comparing one another.

This document is not perfect and I want you to get more information from professional articles.
I’ll have this document get fixed afterterwards.
Also, pointing out any of the errors is always welcomed.


< ReplayGain(RG) >

This technology is done by analyzing the internal volume of a music file.
Then, by calculating the difference between the volume and the target volume, the number is put in the tag of the file.
When a music player or a device plays the file, it reads the tag of it.
If there’s a RG data and the player notices it, the difference is applied to the output volume when the player is playing the file.
This means that RG tag does not change the sound wave of an audio file.
All the analized data are put in the tag and this means that if you remove the tag, then the analyzation is gone.
Then the file will become the one which was like before the RG analyzation.


< MP3Gain >

The core algorithm is the same as ReplayGain.
MP3Gain is a program designed to apply the RG technology to MP3 files.
Because RG just calculates the difference of the file volume and the target volume and then put the result in the tag, it supports all file types.
However, the problem is that the music player should be able to read and use the RG result.
Years ago, old devices and programs could not read and apply the RG analysis result in the tag.
So the analyzing was no use.
In order to solve this problem, MP3Gain was developed.
It uses the RG algorithm and applies the result to the actual audio file.
It does not just add some number in the tag, but it really changes the actual volume of a file.
Because the process is done by really changing the sound, this program only supports MP3 files.
Other file formats require different ways of processing, so there are similar programs such as AACGain for other formats.

In the official site of MP3Gain, it says that the program does not change the original file.
It’s a half truth.
It actually changes the internal volume of a file and then adds a tag about the amount of volume change.
The type of the tag is APE.
When you want to remove the change, MP3Gain reads the tag and redo the change.
But when you remove the APE tag after changing the volume once, the audio file cannot get back to the original state by itself, if you don’t remember the original volume or the amount of change made by MP3Gain.
To add, it is a small defect that MP3Gain can only change the volume by 1.5dB.

< Sound Check (iTunes) >

Sound Check is a feature provided with Apple’s iTunes.
The basic mechanism is just like ReplayGain.
iTunes automatically calculate the volume of any files such as AAC and MP3.
Then, iTunes add a tag to the file about the difference of the volume level compared to the target leve.

There are some disadvantages.
Because it’s Apple’s own technology, the tag made by Sound Check is not always applied to devices or programs that are not made by Apple.
Also, while the Sound Check is done relatively quickly, the analysis is not that accurate.
iTunes’ target level cannot be changed manually by users in a normal way.
Lastly, because the volume change is done on files one by one, you cannot do an ‘Album Gain’.

However, all the defects can be solved if you use a program named iVolume.
You can do ‘Album Gain’, you can change the target volume as you want, and the analysis is done quite specifically.
iVolume can be used freely, but to remove some inconvenience you should pay for the app.
The first defect can be solved when you change all your devices to those made by Apple. lol


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