Hey, long time lurker finally asking a question here,I was wondering exactly how iTunes Sound Check worked.

I know it scans all files like ReplayGain and makes a small addition to its tags to modify volume, but to what level are the files normalized on playback? I know ReplayGain puts in either a negative or positive gain value to get the files to 89 dB, and I also know that ReplayGain can preserve the volume differences between tracks on an album by using the album scan function; rather than normalize them all to 89 dB and lose the differences between tracks in the process.

Does iTunes Sound Check normalize ALL files to a certain level (and what is that level?), or does it do it "interalbum", for lack of a better term? I really wish I could use ReplayGain, but I'd either have to normalize the files themselves before compression (NOT an option, my library is Apple Lossless, emphasis on the word LOSSLESS, I don't want to modify the actual data) or get a different DAP and/or ditch iTunes.

You can replaygain scan ALAC files in foobar and then upload the replaygain values as sound check tags to your Ipod. I've been doing it for a couple years now, and it works great.

From the HydrogenAudio.org Wiki:

"However, it also allows the loudness of an album to be consistant over a entire music collection, allowing the dynamics of album to remain (This is called 'Album Gain', or 'Audiophile Gain' in earlier parlance)."

Also:

"The iPod features Soundcheck, which seems to produce roughly the same normalization gains as replaygain, but doesn't provide an Album Gain."

So, you're saying I could do an album gain scan using fb2k's RG, and then use some software to modify the M4A tags with the proper information. Would iTunes touch Sound Check data AFTER it's been added to the file? I don't want to go through the trouble of doing an album gain scan on every album I've got, and then have iTunes haphazardly rewrite all the tags with plain old, per-track Sound Check data.

Not too many iTunes users on HA?

I would like to know the answer to and how to add the RG data replacing Soundcheck data. I rarely use iTunes but I do use my iPod 2nd Gen Nano.

Thats certainly possible to do, but I have no idea if any software to actually do it has ever been written. I'm saying you can use foobar (w/ foo_dop plugin) to add the sound check info to your iPod. If you want iTunes to understand it, you'll have to find something that could actually change the tags as well.

But he's still stuck with no album gain values, since SoundCheck tags don't support the concept, right?

I would Rockbox that iPod. I would think it's a lot easier to just use software that supports replaygain than try to simulate it.

No one has written a utility yet that lets you scan/replace the iTunes Soundcheck data with ReplayGain-derived data. Unfortunately, this prevents anyone using iTunes from having something like "album gain". All Soundcheck data generated by iTunes is the equivelant of "track gain".

In theory, it shouldn't be too difficult to write a utility that would update the iTunes database to scan the files for the track/album replaygain data and then let you switch between track/album soundcheck data as wanted. The iTunes database is XML after all.

The folks who worked on the Foobar iPod plugin already figured out how to convert replaygain data into soundcheck.

Of course, I am no programmer

Wouldn't it just be possible to use Foobar to generate album gain info for the files, then manually copy the values into the track gain field instead, and then use whatever converter it is you're talking about?

You can write whatever you like to the sound check field. Album or track gain, although obviously you have to choose up front which one you're going to use.



The converter hes talking about actually calculates a sound check value from a replaygain value, the two systems don't store values the same way. If you're interested, theres some posts of mine from late 2003 or early 2004 where I posted the details for the conversion by calculating SC and RG values for a couple songs and plotting them. Its in one of the old foo_pod threads I think. If you wanted to do this by hand, you could use a calculator and the conversion formula from that thread.

So, I could calculate album gain values using foobar, which would store the values in its own database anyways as, AFAIK, it can't write RG info to AAC/ALAC, convert the RG values to their SC equivalents, and then enter them by hand into the ALAC tags using foobar? I'll do a search for the threads in the meantime.

I doubt foobar can write the soundcheck fields into tags. I'm not sure if there is software that can (short of a hex editor!)

Winamp converts the track replaygain to soundcheck data before transferring to an iPod. The next version will choose track or album, based on your preferences, but the current version is hardcoded for track gain.

Mp3tag can create soundcheck tags for mp3 and aac files.
For aac, you just need to create a new tag with the name ITUNNORM.

The next version will also have a function that converts replaygain values to soundcheck values so all you need to do is use foobar to calculate the RG data and then let Mp3tag batch convert/tag the soundcheck stuff..

OK, reading this thread: http://www.hydrogenaudio.org/forums/index....=0&p=373432 and this thread: http://www.hydrogenaudio.org/forums/index....showtopic=19156 have made it clear to me that at least some amount of people here at HA have figured out:
1. How to convert RG gain values to SC hex values
2. Where SC values are stored

I'm not clear on #2 though; does iTunes store the SC info in the "ITUNNORM" tag foobar can see on so many of my ALAC files? Is it in the XML or ITL files in My Music/iTunes? On the iPod in iTunesDB? Or in a combination of the three?

I use iTunes for maintaining my library (play counts, ratings, album art, etc.) and use it to autosync everything to my iPod, so using fb2k 0.8.* with foo_pod is out of the question. There IS a solution to my problem, I'm just not able to piece it together.

Some cliff notes you guys might find useful:
1. All of the Apple Lossless files in question DO have ITUNNORM tags; I've never enabled Sound Check before though, neither on my iPod or in iTunes. The one or two hundred MP3s in my library do not have Sound Check tags though.
2. There are NO FILES in my library with ReplayGain tags, be it Album Gain or Track Gain.
3. I do not use foobar to manage my music library in any way; I use iTunes. But foobar still kicks ass for file conversions, and handling CUE sheets.
4. I appreciate all the help, HA is always there for me when I have silly, audio related questions .

bump

iVolume does this, but it's Mac-only. I use it for album-gain. It works perfectly.

No, he would just have switched itunes over from track gain to album gain mode. What iTunes does not support is using both.



Unfortunately it is not...the xml file is a replica of the database itself, which is in the .itl file. So editing it won't accomplish anything.
You can delete your database and the re-import the xml file to recreate it but unfortunately not all fields are in the xml file and some fields which are, are not used during the re-import. I haven to tried this personally though, maybe somebody who has can confirm this?




See above. The library is in the itl file but itunes creates a copy of it in xml format for other programs to use. (the idea is that you could write a program which uses information from itunes; you can get this from the xml file)
The ipod has a separate database which is filled by itunes (or whatever you use that supports it) when syncing. This allow you to go beyond mere id3 tags on the ipod and use lets you e.g. rate songs on the ipod and have them synced back to your pc, or have the playcounts of all songs you played on the ipod get synced back to your pc. (handy for smartlists)

Since I made the mistake of aacgaining all my aac files after I put them in itunes, i have a lot of aac files with a wrong soundcheck value. Currently I know of only one way to remove the soundcheck value:
1) remove the files from itunes
2) remove the itunnorm tag in them
3) re-import
Unfortunately, this would make me lose all my ratings and playcounts, so I would be very happy if somebody could find a way to delete the soundcheck value. (editing it would be even better)

I haven't enabled Sound Check in iTunes or done any MP3Gain/AACGain/ReplayGain scans on any files in my library; I'm assuming that puts me in a better position if I decide to try and do any RG/SC work to my Apple Lossless files and/or MP3s?

Correct. The problem is that there's no way to remove or edit current soundcheck values in itunes using existing software. So, if you scan it and then mp3gain/aacgain a song, the soundcheck value is no longer correct.

The previously-mentioned iVolume program for mac also is not a good solution: the only thing it seems to do is change the itunnorm tags in the files. You still need to re-import the files for the new value to get read.

My experience actually using iVolume contradicts this. It works fine without re-importing the files.

Wow, lots of info in this thread. Basically, if I don't want to jeopardize being able to have Sound Check values based on a per-album value (using a 3rd party tool), I should hold off on enabling Sound Check?

Quick question because the huge volume differences between the tracks in my library is driving me insane (going from tracks off U2's first album, to their most recent, makes my ears explode); if I want to listen to an entire album on my iPod and want to preserve the volume differences between tracks, I can just shut Sound Check off in the settings and then turn it back on when I'm back to listening in shuffle mode, right?

Correct.

Whoa, just when I was about to give up, this post shows up. I always tried deleting the itunnorm value to have itunes recalculate. While this does indeed does not seem possible, using this method you can at least change it to a correct value by doing a 'get info'.

So:

• replay-gain scan using foobar to get the track or album gain value
• Convert this using mp3tag using the rg2sc() function in combination with the 'format value' action
• refresh file info in itunes. (or play file)

This, in combination with the vbscript to update the library from tags, should take care of things...