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Topic: AACGain & iPod (Read 9150 times) previous topic - next topic
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AACGain & iPod

Hi there all.

Last week I used MP3Gain to "normalise" the 2777 AAC files on my iPod.

I undertook the "Track Analysis" then applied the "Track Gain".  According to MP3 Gain all my song files have now been normalised to 89dB.

However after I connected my iPod, I did not note any change in dB levels.  Additionally, the iTunes did not recognise any changes in volume levles (still reading -4dB for some songs and +4 dB for other etc...),

Does anyone know why the Track Gain tool did not effect the AAC files properly ?

Much appreciated, garethg.

AACGain & iPod

Reply #1 –
>Additionally, the iTunes did not recognise any changes in volume levles (still reading -4dB for some songs and +4 dB for other etc...),

Unless you were able to get iTunes to rescan the files by removing the iTunNorm tag from them and removing/readding them to the iTunes library, iTunes won't notice any difference. It doesn't rescan just from changing the file, you have to trick it into doing it. Pain in the ass, actually. Best to just disable SoundCheck entirely if you're using MP3Gain or AACGain or similar.

AACGain & iPod

Reply #2 –
Am I correct in thinking that having SoundCheck "on" takes additional processing power and thus will shorten battery life?  I assume that is one reason why people are using AACGain instead.

AACGain & iPod

Reply #3 –
thanks.  how do I remove the iTunNorm tags from the files ?  would simply re-setting the iPod itself, deleting the files from iTunes library, then re-importing the files into iTunes work do you think ? 


Quote
>Additionally, the iTunes did not recognise any changes in volume levles (still reading -4dB for some songs and +4 dB for other etc...),

Unless you were able to get iTunes to rescan the files by removing the iTunNorm tag from them and removing/readding them to the iTunes library, iTunes won't notice any difference. It doesn't rescan just from changing the file, you have to trick it into doing it. Pain in the ass, actually. Best to just disable SoundCheck entirely if you're using MP3Gain or AACGain or similar.
[a href="index.php?act=findpost&pid=267697"][{POST_SNAPBACK}][/a]

AACGain & iPod

Reply #4 –
Quote
Am I correct in thinking that having SoundCheck "on" takes additional processing power and thus will shorten battery life?  I assume that is one reason why people are using AACGain instead.
[a href="index.php?act=findpost&pid=268041"][{POST_SNAPBACK}][/a]

Actually, since SoundCheck nearly always reduces the volume, I'm thinking that it'd probably save battery in the long run. The extra processing is basically reading a few bytes out of the iTunesDB file and setting it in the amp or whatever the iPod has for that. I don't think it'd take any extra CPU. Same with the EQ, that's applied after the thing is decoded into analog, I think.

The only reason I can think to use AACGain is that it uses the ReplayGain methodology which is more accurate than SoundCheck is, and if you used foo_pod you wouldn't have to bother, since foo_pod can convert the ReplayGain info into SoundCheck info for the iPod to use.


garethg: Sorry, I don't know. I'm not real familiar with M4A tagging. For MP3's you can just remove the extra COMM field that it adds to the tag, using whatever tagging program you like best.

AACGain & iPod

Reply #5 –
Quote
thanks.  how do I remove the iTunNorm tags from the files ?  would simply re-setting the iPod itself, deleting the files from iTunes library, then re-importing the files into iTunes work do you think ?


I wouldn't recommend removing the iTunNorm tag. I've seen posts that imply that iTunes won't recocognize a file with this tag missing, although I've never tried it myself.

Resetting the iPod will work.

Also I've noticed that changing metadata causes files to be reloaded to iPod. If there's a field you don't use (e.g comment), then select all songs in your library and use GetInfo to change that tag for all songs.

HTH...

Dave

AACGain & iPod

Reply #6 –
Is there a frontend for aacgain.exe? I can't find one any where.

AACGain & iPod

Reply #8 –
How? Do I add the accgain.exe in the install folder?

AACGain & iPod

Reply #10 –
Quote
I wouldn't recommend removing the iTunNorm tag. I've seen posts that imply that iTunes won't recocognize a file with this tag missing, although I've never tried it myself.

This is not true, although I admit you can screw it up, possibly.

If iTunes is passed a proper file without the iTunNorm tag, it should scan the actual content of the file and then add the tag. The iTunNorm tag is what contains the volume data. If you give it a file with a bad iTunNorm tag (which it will be after AACGaining it), then it will assume the iTunNorm tag has the correct data (which it no longer does).

Quote
Resetting the iPod will work.

In the sense that it will force the files to be resent to the iPod, yes.
In the sense that it will correct the dB shown for the AAC files in Get Info and make SoundCheck work properly again, no.

AACGain & iPod

Reply #11 –
Quote
If iTunes is passed a proper file without the iTunNorm tag, it should scan the actual content of the file and then add the tag. The iTunNorm tag is what contains the volume data. If you give it a file with a bad iTunNorm tag (which it will be after AACGaining it), then it will assume the iTunNorm tag has the correct data (which it no longer does).


Are you suggesting that AACGain delete the iTunNorm tag? Will this cause iTunes to automatically sync modified tracks to the iPod?

I won't get a chance to test this for a few days, so if anyone knows for sure, please post.

Thanks for the help!

Dave

AACGain & iPod

Reply #12 –
Quote
Are you suggesting that AACGain delete the iTunNorm tag?

Well, I didn't suggest it, exactly, but it is a very good idea for AACGain to do so. The iTunNorm tag contains, among other things, a number that specifies the volume change that iTunes (and by extension, the iPod) should apply in order to volume level the file.

In short, if you look at an iTunNorm tag, the first set of numbers after it is a hexadecimal representation of the "-6.7db" (or whatever) that you'll see in iTunes when you do a Get Info on the file. Without that iTunNorm tag, iTunes should scan the file to determine that proper number. It works for MP3's, definitely. I have not tried it on an M4A file.

However, the file must be REMOVED from iTunes and added back to force it to rescan that file. I have not found another way to force it to do this.

Quote
Will this cause iTunes to automatically sync modified tracks to the iPod?

No, but changing one of the tags in the file will. Not every tag though. BPM, for example, it doesn't care about. Comments it does care about, for some reason. Add a space to the end of the comments or remove a space from the end or something and it'll update the iPod. It still won't rescan for SoundCheck though.

AACGain & iPod

Reply #13 –
Quote
The iTunNorm tag contains, among other things, a number that specifies the volume change that iTunes (and by extension, the iPod) should apply in order to volume level the file.[a href="index.php?act=findpost&pid=297994"][{POST_SNAPBACK}][/a]


Do you (or anyone else) know the algorithm that iTunes uses to create the db level in iTunNORM? Maybe I could recalculate it when aacgain is applied instead of deleting the entire tag? I've also seen other posts claiming that iTunes will fail to read files that are missing this tag, so I would be nervous about deleting it.

Thanks for the help!

Dave
 

AACGain & iPod

Reply #14 –
Quote
Do you (or anyone else) know the algorithm that iTunes uses to create the db level in iTunNORM? Maybe I could recalculate it when aacgain is applied instead of deleting the entire tag?

I thought of that, but no, I don't know the algorithim, nor what most of the fields in that tag actually mean.

Quote
I've also seen other posts claiming that iTunes will fail to read files that are missing this tag, so I would be nervous about deleting it.[a href="index.php?act=findpost&pid=298198"][{POST_SNAPBACK}][/a]

The only thing I can suggest is testing. However, iTunes not reading files lacking it makes no sense, as if that were true, you'd not be able to use Nero's AAC tools to create iTunes compatible AAC files. I think that somebody removed the tag improperly and corrupted their file in some way iTunes didn't like.