I've got about 200 CDs that I normalized and then coded to MPC months ago. These days I'm using Replaygain instead of normalizing. I don't want to rerip all those CDs again so this brings me to a question. I'm just wondering how different in volumes the normalized and Replaygained MPCs will be when all played together. Should I Replaygain all those previously-normalized MPCs or should I leave them alone? Thanks.

shouldn't hurt to replaygain them, and you'll obviously get matching volumes that way

If you apply replaygain to the tracks they will have the same volume as the the other tracks. It does not matter if some were "normalized" or had their volume lowered by 23 dB or whatever. Replaygain makes all files (or albums) the same level.

So go on and replaygain those files...

Track gain will work but album gain will obiviously not work (like it should), because the original differences in loudness between the tracks of an album are lost by normalizing.

well, it'll work, it'll just be giving different, but still valid in terms of the existing data, results

Thanks guys. I just didn't want drastic volume differences between the normalized/replaygained and the replaygained files. I did test a few files and they sounded OK but I didn't know if it was a fluke or what. Cheers.