Frequently called 'dialnorm'. A metadata indication in a Dolby Digital bitstream of the volume level of the dialogue in an audio signal. Dolby Digital decoders can use this 'flag' to adjust the volume level of the whole audio stream, so that the dialogue levels of different programme sources remain the same. Most DVD movies have this flag set to '27', which means -27dBFS. If the decoder is set to act upon this, it will reduce the level of the signal by 4dB because it means that the dialogue is set 4dB higher than the calibration level of -31dBFS. It is important to note that this volume adjustment is made not just to the dialog, but to the entire sound track. It is also important to note that it does nothing to the sound other than adjust the overall volume level. Whether or not the dialogue normalisation feature actually works as hoped -- in the sense of bringing the voice levels of all programmes into line with each other -- depends entirely on the engineers who mix the sound setting the dialogue to the appropriate level in the first place. Dolby Digital encoders typically default to the value of 27, and must be explicitly changed for a different value. Many home theatre receivers report dialogue normalisation with reference not to 0dBFS, but to -31dBFS (the calibration level), and so a level of -27dBFS is reported as -4dB.