what you just described doing is called transcoding and makes your songs sound like crap
if you download variable bit rate mp3 and encode them to a flat 320 or whatever youre transcoding and ruining the sound quality. try to get it in the format you prefer, or if you can't just get FLAC and burn it to a disc and rip them that way.
but DONT UNDER ANY CIRCUMSTANCES re-rip something unless its FLAC
just a tip for sound quality