Have you ever put on an album and noticed that it was drastically louder than the last album you were listening to? Everyone has a few albums that every time you put them on you race for the volume control to turn them down. Similarly, I'm sure you've heard albums that were "too quiet" and you had to turn them up quite a bit to hear them at all (only to go racing for the volume control again when you followed them up with a loud one). This is the result of the fact that (unlike film) there's no loudness standard in audio engineering. Because louder audio is often perceived as sounding better, there has been a "loudness war" in mastering music to try and make the loudest sounding music possible, often through compression (reducing the Dynamic Range to make more of the song "loud"). One unfortunate side effect of the loudness wars is that albums have drastically varying average volume levels.
Volume Leveling is a solution to this problem. It does it by analyzing the "loudness" and dynamic range of the music (using the international standard R128 analysis method), and then adjusting the volume level of the music to a reference level. The result is that most music will sound close to the same average volume with volume leveling on. Volume leveling does not compress the music or affect dynamic range; it just changes playback volume. Volume Leveling also does not alter the audio content of files; all volume adjustment is done using DSP at runtime.
By default, when you play an album, the whole album gets adjusted by a fixed amount so that intertrack dynamics aren't affected (i.e. a "quiet" song on an album will still sound quiet compared to the rest of the album). When you play a mixed playlist, each track is adjusted individually so each track sounds about the same volume (like on the radio).
Because most music is mastered so that its peak level is close to (or sometimes even above) digital full scale, in order for volume leveling to work correctly (without clipping) most music must receive some amount of attenuation (rather than boost). This means that when you first turn it on you'll need to turn up the volume a little; but after that you'll be able to leave the volume control more or less alone.
In order to use volume leveling you'll need to analyze your files first using the Analyze Audio library tool. The information is stored in the database and in the file itself, so that playing the file with any compatible player will play it back at the reference volume.
Media Center includes a stock smartlist that will help you identify files that haven't been analyzed. It's titled "Audio-- Task -- Needs audio analysis," and will show you which files haven't yet been analyzed.
Once you've identified files that need analysis, it's a two-step process. First, the program analyzes your files and determines the gain levels. Second, you must enable the DSP option to apply those levels during playback.
Step 1: Analyze Audio Files
Select files to be analyzed.
- To analyze all files, select files using one of the following methods then go to Tools > Advanced Tools > Analyze Audio:
- Use the smartlist mentioned above; or
- Select an Audio View, then select all files in the content list (Ctrl + A)
- To analyze a few files, select the files in the content pane, right-click and select Library Tools > Analyze Audio.
The Audio Analysis screen shows the files selected. Make sure that "Skip analyzed files" is checked, and select "Analyze".
Wait for the analysis to be complete. This could take a while, depending on the number of files it is analyzing. If you have many files (over 5,000), perhaps you can do this overnight.
Step 2: Enable Volume Leveling
Go to Tools > Options > Audio > DSP Studio & Output Format > and check the box for Volume Leveling.
Auto Analyze during Import or Rip
You can set the program to automatically analyze files when you import them into the library or rip them from a CD to your computer. This setting is enabled by default, but can be changed in Auto-Import configuration or CD Settings.
Technical Information on R128 and Replay Gain
The program uses the R128 analysis method which is the international standard for loudness normalization. The R128 standard targets -23 loudness units below full-scale (equivalent to -23dBFS) as the volume reference level. Media Center's implementation of the standard targets an 83dB output at the reference level. For more information about how to calibrate your system and how this reference level interacts with other portions of Media Center's audio engine, see the articles on Reference Level Calibration and Adaptive Volume.
Prior to adopting R128, Media Center used replaygain analysis for volume leveling. Note that for compatibility, Media Center continues to write replaygain tags so that analyzed files can be used with other players that support the replay gain standard.