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HELP! AACGain on Mac wreaked havoc on my music!, Random volume drops...
post Nov 2 2005, 18:19
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Howdy everybody! Please be gentle, this is my first post, even though I've been lurking for a while.

I recently did a bit of experimenting with an Intel Mac system. I had about 2000 songs in my library on my Windows computer, and I ran them all through MP3Gain to normalize around 89 dB. When I moved to the Mac, I re-normalized everything to play a little more nicely with a few iTMS songs I bought. I used the command line version (I believe 1.4, but don't quote me on that...I'm at work) with the following options:

aacgain -r -p -t -k

Which WREAKED HAVOC on all of my music! Some songs were so quiet you could barely hear them, and other were so loud that they instantly clipped and distorted when they started playing. I tried the aacgain -u undo feature to no avail. I then re-processed the music using the following options:

aacgain -r -p -t -k -s r

The extra -s r is supposed to 'forget' previous AACGain adjustments and re-evaluate the file, which it did. Everything seemed fixed... or so I thought.

After more thorough listening of my music, I found out that about 30-50% of my music randomly drops in volume somewhere in the middle of the song. It's never the same time, and it seems to be roughly in the neighborhood of 10 dB or so.

My guess is that something short-circuited and wrong gain values got written to the frame headers. Subsequent efforts to fix this problem in AACGain have been relatively unsuccessful, since the program applies changes uniformly across the file.

So I guess I have 2 sets of questions:

1) Is there a piece of software that can fix this sort of thing?
-- As much as I HATE to do it, the "last straw" answer seems to be some sort of program that will fix levels radio-style, i.e. some sort of compression. I HATE it, but it might be my only option.

2) Can I maybe hack it myself?
-- I'm no programming whiz, but I do have some experience. I've thought about getting the source for AACGain and seeing if I can somehow force the frame headers to the correct gain. Which brings me to another question:

2a) Is the gain within an mp3 file fairly constant throughout the different frames, or does it change between frames in a single song?
-- If not, I could just grab the gain from the first several frames and apply it across the rest of the song. If not, it could get more interesting...

Many people here seem very knowledgeable about this sort of thing. Please help!
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