The maximum absolute value of instantaneous sound pressure for any specified time interval. The most common unit is the microbar.
"Am I delighted! We had all treasured a little 78 that Daddy sent his parents from Germany while in Army during WW2. The surface was trying to crack, so I knew I needed professional help to archive it to MP3, which might actually be impossible. In fact, Dr. Coban sent me an extraordinary MP3 that was more clear than when we played it a ..."