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Dialnorm is the meta-data parameter that controls playback gain within the Dolby Laboratories Dolby Digital (AC-3) audio compression system. Dialnorm is an integer value with range 1 to 31 corresponding to a playback gain of -30 to 0 dB (unity) respectively. Higher values afford more headroom and are appropriate for dynamic material such as an action film. Dolby recommends that the dialnorm value be determined by measurement of average dialog level in the encoded audio of every program. The recommended approach derives the absolute value of a power sum of the A-weighted audio level in all digital channels. If every producer and distributor uses this method, consumer dialog levels will be consistent from program to program and channel to channel. The dialog levels will be "normalized" - hence the abbreviation "dialog normalization". ==Historical Basis== Audio levels within analog disk, tape and broadcasting have traditionally been adjusted to keep peak levels within the physical and legal modulation limits of the medium. While this practice has resulted in relatively consistent dialog levels and has minimized audibility of channel noise, it has come with a severe penalty in the form of excessive audio compression and limited dynamic range. Digital recording has eliminated the concern for noise, but the lack of a standard for digital audio level has resulted in compact disk recordings and portable music player files with widely varying levels. Increasingly, digital music is excessively compressed, to ensure that the selection is not perceived by the listener as being too soft in comparison with other sources. Dolby Laboratories sought to provide wide dynamic range and consistent audio levels in the Dolby Digital encoding system. One approach would have been to require audio levels at the encoder input to be adjusted to a fixed value. Instead, AC3 allows producers to choose input level over a wide range, by including a required dialnorm value representing the measured dialog level of the input signal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dialnorm」の詳細全文を読む スポンサード リンク
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