What is "dialnorm"

Dialnorm is the metadata parameter that controls playback gain within the Dolby Laboratories Dolby Digital (AC-3) audio compression system. Dialnorm stands for dialog normalization. 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 program. The recommended metering approach uses a power sum of the A-weighted audio level in all 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.