"The recording of AC/DC's next album took place in Paris with "Mutt" Lange and the task wasn't proving easy. The main cause of concern was the fact that Lange was apparently finding it difficult to get the right kind of sound for the record. Lange solved the sound problems by hiring a mobile recording unit from England."

"AC/DC which had not previously recorded outside Australia and had never spent more than 3 weeks working on an album spent 6 months in the Roundhouse Studios with "Mutt" Lange working on the new record. Lange did an admirable job of refining and sharpening AC/DC's sound without losing the raw edge that was the source of the band's original appeal."

From an interview with Angus Young of AC/DC:

Q: Did Mutt Lange demand a lot of retakes?

A: Mutt's very much a sound guy. With AC/DC that was his big thing. He was always trying to get tuned in on the sound quality; we were always one for the groove quality and the song quality. (thanks to Jack -zephyr 102)