Dolby Atmos for mobile

Audio objects

With Dolby Atmos®, any sound can be rendered as a single audio element, an object, independent from the rest of the soundtrack. A child yelling, a helicopter taking off, a blaring car horn — the filmmaker can decide exactly where the sound should originate and where it should move as the scene develops.

Audio objects allow filmmakers to concentrate on the story. For channel-based audio, filmmakers can only approximate a sound's desired location and cannot isolate individual sounds. With Dolby Atmos, filmmakers choose precisely where the sound should be located, and the system intelligently makes the speaker-assignment decisions based on the speaker array in the theater or home. Audio objects originate and move anywhere in three-dimensional space, including anywhere overhead.

Headphones and built-in stereo speakers

While cinema and home theater systems have multiple channels, the headphones and built-in speakers of mobile devices are two-channel stereo. To create the Dolby Atmos experience for mobile users, Dolby scientists drew on their extensive research and expertise in psychoacoustics, the study of how we perceive sound.

Creating a realistic perception of height and surround sound two-channel mobile systems begins with head-related transfer functions (HRTFs). HRTFs describe how incoming sounds located at different positions around us arrive at our ears.

Depending on where a sound originates, it may arrive at one ear very slightly later than at the other, and it may have slightly different characteristics at each ear (such as being softer or less distinct). The differences are caused by interference from the listener's head, torso, and external ears. The brain instantly processes these differences as spatial information, enabling us to hear in three dimensions. HRTFs represent these same differences mathematically.

HRTFs make magic

A streaming-media Dolby Atmos mix supports up to 128 simultaneous audio objects and includes metadata that describes the location of each one in space. The Dolby Atmos processor on a mobile device applies our extensive sets of HRTFs to this metadata to recreate the spatial information in a stereo signal. Heard over any headphones or earbuds, this stereo soundtrack accurately simulates the theatrical sound, including sounds from above, for a powerful and spacious experience.

To reproduce this same experience over a device's built-in speakers requires additional processing. Speakers generate a natural "crosstalk" phenomenon at our ears that works against simulating multiple channels. The Dolby Atmos processor cancels this crosstalk and then applies the HRTFs to create the dimensional soundstage and movement of the audio objects.

As an added benefit — and bit of magic — the Dolby Atmos processor delivers all this with minimal effect on battery life.