In creating the CD versions, the recordngs have been remastered a number of times.
US/Reprise (mastered by Lee Hershberg)
UK/Polydor (different from Reprise above)
US/Reprise (remastered by Joe Gastwirt using NoNoise; "RE-1" on inner ring of CDs)
UK/Polydor (clones of the second issue Reprise discs?)
US/MCA (remastered by Joe Gastwirt, don't know if NoNoise was used or not; alternate covers; also issued by Polydor overseas)
MCA/Experience Hendrix (remastered by George Marino/Eddie Kramer)
Thanks to Luke for this information !
Note that the current MCA CDs have compressed sound ! The high frequencies are simply not there. The previous series had a fuller sound. Read more on Posthumous Studio Releases - 90s page.
Thanks to Paul for underlining this.