Loudness Normalization in the Age of Portable Media Players

In recent years, the increasing popularity of portable media devices among consumers has created new and unique audio challenges for content creators, distributors as well as device manufacturers. Many of the latest devices are capable of supporting a broad range of content types and media formats including those often associated with high quality (wider dynamic-range) experiences such as HDTV, Blu-ray or DVD. However, portable media devices are generally challenged in terms of maintaining consistent loudness and intelligibility across varying media and content types on either their internal speaker(s) and/or headphone outputs. This paper proposes a nondestructive method to control playback loudness and dynamic range on portable devices based on a worldwide standard for loudness measurement as defined by the ITU. In addition the proposed method is compatible to existing playback software and audio content following the Replay Gain (www.replaygain.org) proposal. In the course of the paper the current landscape of loudness levels across varying media and content types is described and new and nondestructive concepts targeted at addressing consistent loudness and intelligibility for portable media players are introduced.