I guess the title of the thread says it all... Is there an AAC Gain program? If not, could one work like MP3Gain does, ie the lossess approach

Umm, no, not at the moment. And anyway.. MPC/Vorbis' header approach is even more "lossless" because the bitstream is not touched at all, information is only written to the header.

MP3gain changes the actual bitstream, and although it's reversible process, I'd consider header approach even more "lossless" (if you lose the log files of MP3gain, you won't be able to reverse back to the original volume). But when the info is in the header, you can choose to use the original volume or title- or album gain, so I consider it even more "lossless". Of course the bad point of header based replaygain is the need of decoder support.

Anyway, maybe Ivan can tell if there's similar to mp3 global gain factors in AAC bitstream which can be tweaked?

Yes, AAC has "global gain" (first quantizer scale factor) - it is possible to decrease the volume by adjusting the global gain SFB, but I haven't noticed that someone has done this tool.

Yes certainly the MPC/Vorbis header method is even better then the almost-lossess MP3Gain way I guess I forgot about this way as I have not tried MPC and OGG (yet).

Form what Ivan has said, I assume that if the "global gain" of AAC used, then we would be in a similar position as MP3Gain, ie we loose the original gain value. From what I can tell, the AAC stream doesn't cater for the extra headers that a MPC/OGG gain method would require - but could an MP4 stream containing AAC allow for this?

Also, is it just me but do you think the term 'Radio Gain' is a bit missleading? I much rather call it track gain or as JohnV says title gain. Radio sort of suggests a quality measue to me.

where can i find the spec of AAC headers ?
i want to support AAC in BeSplit (streams splitter/corrector), and mayB add one-pass normalization for AAC into BeSweet (only MP3 & Ogg are possible now).

I guess some info can be found on MP3-tech's "Programmers Corner"

http://www.mp3-tech.org/programmer/programmers.html

Regards;

Roberto.

Check out the FAAD decoder at www.audiocoding.com - it has a very nice interface to AAC bitstream elements.

Also, draft ("beta") version of the MPEG-4 specification could be downloaded from:

ftp://ftp.tnt.uni-hannover.de/pub/MPEG/au...ocuments/w2203/

yea, i already have the faad sources, but i believe there must be a better way to learn AAC structure, rather than doing reverse engineering to a decoder source code .

it would be cool if i could get my hands on iso 13818-7, but something like this shall suffice .

ftp://ftp.tnt.uni-hannover.de/pub/MPEG/au...03/w2203tfa.pdf

From page 74


Note - this is a working draft of MPEG-4 spec, and it is more than 4 years old - it is a better idea to buy official MPEG-4 standard with corrigenda, but this is enough for your needs.

looks like w2203tfs.pdf is the answer.
10q, Ivan .

btw, i found the standard (iso 13818-7) at work, so now i have a hard-copy of it.

Now that it's been a couple years, I'm curious if an app ever showed up?

http://www.hydrogenaudio.org/forums/index....0141&hl=aacgain

Thanks Jan S.
Here's hoping for an OS X version soon.