<solution> Last night, after much frustration I finally sat down to resolve this same pip boy radio music problem (soundblaster xfi extremegamer on windows 7 64). Read all of this post and tried the following. Installed madfilter. Installed k-lite codec pack. Neither helped. Rebooted and installed the CCCP codec pack. No change. Alchemy was already installed. I then installed the installedcodec utility, which shows you a large and comprehensive list of all your installed codecs. This seemed helpful, because you can individually enable or disable any codec right there without closing the program. So, I simply disabled everything and entered fallout3. No world music, no pip boy radio music. But the other effects sounds were present. Good start. Went back into installedcodec, since by now I realized that this was likely a codec conflict problem. Proceeded to systematically enable clumps of codecs that appeared relevant to MP3 music, since MP3 is the format used to play the radio music in pip boy. I would then reenter the fallout title menu quickly just to see if the menu music was present. This saved me time, so that I did not need to go all the way into a saved game to see if the changes I made would reenable the music. Eventually found the culprit codec. It was a media streaming codec installed by a WMA to MP3 conversion program I downloaded from the net somewhere. I uninstalled that program and immediately noticed a large amount of codecs disappear from the installedcodec listing. Entered fallout and enjoyed perfect radio music with no stutter and perhaps a slight fps boost to boot.
