Re: [Bug-gnupod] Patch to support ReplayGain / mp3gain

[Richard van den Berg]

On 5/7/09 5:06 PM, H. Langos wrote:
> Nowerdays I wouldn't let it come anywhere near my iPod. :-)
>   

I'm still practicing on my 30GB iPod until I convert it to a 240GB one. 
After that I guess I won't risk iTunes screwing it up either. It really 
blows.

> What's important is the fact that there seems to be a standard that defines
> how volume adjustment data can be stored in id3 tags.

Nice research. RVA2 is definitely the standard to use, and gnupod 
already has support for it. The problem is that there is not a lot of 
software that writes RVA2 tags. (The only ones I know about are iTunes 
and normalize). mp3gain should really be changed to write RVA2 tags 
instead of APE ones.

> So I wonder why the author of mp3gain decided to store the information in an
> ascii APE tags comment instead of using the existing standard. (He definetly 
> was aware of it as he states in the FAQ that he "uses David Robinson's 
> Replay Gain algorithm to calculate how loud the file actually sounds to a 
> human's ears.")
>   

mp3gain is one of  the first implementations of the Replay Gain 
algorithm for mp3 files. Please note that the algorithm for calculating 
the volume adjustment in itself has nothing to do with the way of 
storing it. I think mp3gain predates the RVAD/RVA2 standards so they 
went for an APE tag instead. It would have been nicer if they had stuck 
it in a custom X??? ID3 frame instead. It would have been easier to port 
it to RVA2 now.

> I took a look at the source code of normalize and it seems to be able to 
> write to id3v2.3 using XRVA and id3v2.4 using RVA2. Maybe this would be
> interesting for you too? http://normalize.nongnu.org/
>   

I used normalize for a long time before I switched to mp3gain. Normalize 
is nice, but the mp3gain algorithm is better. And I like the concept of 
not altering the data, but just tagging it and only changing the volume 
during playback. It seems normalize can do that now too. The way I used 
normalize (before mp3 support was added) was letting it change the 
volume of the wav files before encoding them to mp3.

Cheers,

Richard