EAC peak levels

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When ripping a CD, Exact Audio Copy (EAC) reports the peak levels ("loudest" samples) present on each track. These values are often used to distinguish different masterings of a single release.

Under most circumstances, differences in EAC-reported peak values are virtually certain to mean the pressings in questions have different audio content -- the exception being those rare occasions where a change in the CD's index points places a peak value in a different track on the disc. But identical peak values are not a guarantee of identical mastering, for several reasons:

  • EAC's percentages are much lower precision (0.0% to 100.0%) than the actual 16-bit samples on a CD (-32768 to +32767). Each tenth of a "percentage point" can cover any of over sixty actual sample values.
  • Peaks cannot distinguish releases with phase-reversed channels, because EAC does not report whether a peak value is positive or negative.
  • Peaks cannot distinguish releases whose channels are swapped, as EAC reports the highest value in the entire track regardless of channel.
  • Some masterings are normalized or compressed such that most or all tracks on the release have a "peak" of 0dB (100.0%).

Use of an analysis tool such as SoX, which reports exact sample values, including phase and channel, is a more precise way to compare the contents of CDs one doesn't have on hand.

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