According to Dolby:
[B]How does Dolby Volume work?[/B]
Dolby Volume measures, analyzes, and maintains volume levels based on how people perceive sound. It examines a variety of audio parameters to maintain consistent playback levels whether switching between channels or between multiple source inputs. A sophisticated combination of spectral- and time-based loudness analysis enables it to quickly and properly correct level differences without creating compression artifacts or undesirable pumping in the audio signal.
In addition, Dolby Volume properly balances low, middle, and high frequencies to maintain all the nuances and impact of the program material regardless of playback volume levels. At both high and low volume levels, it guarantees a listening experience that includes all the dynamics and timbre of the original mix.
[B]Does Dolby Volume introduce artifacts?[/B]
No: unlike previous volume management solutions, Dolby Volume does not introduce audible artifacts or side effects. Quiet background sounds, for example, do not pump up and down between stretches of dialogue, as happens with conventional compression technologies. Content sounds natural and properly balanced even as the playback level remains constant across widely varying program sources.
[B]How is Dolby Volume different from conventional AGC or audio compressor technologies?[/B]
Typical automatic gain controls (AGCs) or audio compressor technologies monitor an audio signalâ€™s amplitude level and not its loudness. To properly solve the reference level playback and loudness level inconsistencies issues, the audio must ideally be monitored and processed in the perceptual loudness domain. In addition, AGC and compressor technologies do not have the same sophisticated cognitive model that Dolby Volume has. Also, typical AGC and audio compressor technologies use a single or small number of audio bands, which are dramatically fewer than the number of perceptual audio bands in human hearing. Because they use crude processing techniques, solutions prior to Dolby Volume can introduce extremely audible and annoying artifacts (such as pumping and breathing).