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Topic: How iGain (AACGain) interacts with Volume Adjustment in Get Info

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Old 02-13-2008, 11:48 AM
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Junior Lounger
 
Join Date: Jul 2005
Posts: 26
How iGain (AACGain) interacts with Volume Adjustment in Get Info

While learning about iGain (and therefore AACGain) in the past few days, I've come across several forum posts here in iPodLounge and various other places found via Google that all indicate a *lot* of user confusion about how iGain/AACGain interacts with the Volume Adjustment slider in the Get Info window of iTunes.


How iGain/AACGain interacts with the Volume Adjustment slider in Get Info

Note: This information is accurate (and tested) in both iTunes 7.5 and 7.6.

To ensure that you get the expected results from using iGain/AACGain on the MP3 and AAC files in your iTunes library, you should ensure that the Volume Adjustment slider (located on the Get Info page for a song) for all songs adjusted with iGain/AACGain is set to None.

Fortunately, it does not matter whether you do this before or after processing your AAC files with iGain/AACGain, because the Volume Adjustment slider merely sets a tag value that only iTunes and iPods know how to interpret. This tag value does not affect the actual data that iGain/AACGain is analyzing nor the gain adjustments performed by iGain/AACGain.

What is important, however, is that if a plus or minus Volume Adjustment still exists on a song that has been processed by iGain/AACGain, iTunes and iPods will correspondingly change the volume of the song from the new volume set by iGain/AACGain. Your iTunes library will not playback as correctly normalized until you reset the Volume Adjustment to None for every song in your library.

Don't fret, this is easy to do!

1. In iTunes, in the Music section of your LIBRARY, ensure that all songs are displayed by choosing All in the Genre, Artist, and Album sections of the Browser pane.

2. In the song list pane, click any song to select it.

3. Press Ctrl-A to select all songs in the list.

4. Press Crtl-i to open the Multiple Item Information window (click Yes if asked whether you want to edit information for multiple items). The Multiple Item Information window appears, and the Volume Adjustment slider will be set to None. Don't worry, this is okay!

5. Drag the Volume Adjustment slider *away* from None and back to exactly None (you need a steady hand and good eye here, unfortunately). A check mark appears in the checkbox next to Volume Adjustment.

6. Click OK. iTunes displays progress as it walks through all of the selected files and sets the Volume Adjustment for each to None. It takes roughly a minute or two per thousand songs.

Remember, it doesn't matter whether you do this before or after having used iGain/AACGain; all that matters is that you do this at some point to ensure that your songs actually play back at the same relative volume as set by iGain/AACGain.


Verifying my assertions for yourself:

You can verify everything I've asserted by carefully setting the Volume Adjustment slider (using the Get Info page in iTunes) on ONLY TWO songs from an entire album *before* ever analyzing those songs with iGain. Set the Volume slider on one of the songs to +100%. Set the volume slider on the other song to -100%. Leave the rest of the songs at None. Next, listen to the songs from that album in iTunes. The +100% one will be much louder than the unchanged (None) songs. The -100% one will be much softer.

Next, use iGain to *analyze* 3 songs from that album: the +100% song, the -100% song, and one of the unchanged (None) songs. (Don't Apply Gain; you just want the analysis right now.) You'll see that all 3 songs have essentially the same Volume and Gain values. This proves that iGain/AACGain is ignoring the value of the Volume Adjustment slider. Or to put it another way, the Volume Adjustment slider value is obviously saved in a metadata tag that only iTunes and iPods interpret; the slider does not affect the actual frame data that AACGain is analyzing (and changing when it applies gain).

Finally, use iGain to Apply Gain to the 3 songs you just analyzed. Now go listen to the 3 gain-adjusted songs in iTunes. The +100% song is still louder, and the -100% song is still softer than the unchanged (None) song. but all 3 songs sound different than before! Next, in iTunes multi-select the 2 songs that you changed and drag the Volume Adjustment slider away from None and back to exactly None and apply the change. Now listen to all 3 songs again. You'll see that all 3 sound the same in terms of relative loudness, and that all 3 sound different from the other songs on the album that were not analyzed/changed with iGain.
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