I've been reading about this topic to try and get my head around it, so I have fragments of info but am having trouble tying it all together and wondered if any people here might be able to help?!
I've been slowly ripping through my CD collection using dBpoweramp; ripping to FLAC and Mp3 at the same time. I use a ReplayGain DSP in the programme to write Track and Album RG (EBU R128 -18 LUFS). Track and Album peaks reach a maximum of 1.000000; never above. I have learnt that in DBPA the RG is calculated on the source material, and the results are therefore always the same for FLAC and Mp3. If done AFTER the encoding, there would be slight differences.
Aside from my CDs, I have a bunch of random Mp3s and FLACs that people have given me, I've downloaded, etc. I've been sorting them out, tagging them, and so on, and have now come to add RG tags. I ran a small selection of them through the RG codec in DBPA (mostly Mp3s) and noticed immediately that a lot of the Track and Album peaks were higher than 1.000000. Some were a lot higher.
From what little I can get my head around, I think this is something to do with the fact they are Mp3s. And this would make sense in the light of the CD ripping I've done seeing as the RG is calculated on source (CD). I'm guessing now that if I re-did the RG on some of those ripped Mp3s properly, I'd start to see some +1 peak values that weren't there before. That is a guess though, so maybe I should try it out to find out for sure....
Anyhow, I wondered first and foremost whether these +1 peak values are to be expected when adding RG tags directly to Mp3s? Are they a problem at all and if so how might problems might be caused. I also like to get my head around these kinds of things as much as possible, so any explanation would be much appreciated too.