Science & Tech

Hearing Is Believing: Comparing Dolby AC-4 to Dolby AC-3

The introduction of Dolby® AC-4 extends the visionary leadership of Dolby Digital while proclaiming the arrival of next-generation audio. Dolby AC-4 is ready now to power the future of audio by enabling extraordinary new audio experiences for content creators, broadcasters, and consumers alike.

Dolby AC-4 delivers on the promise of immersive and personalized next-gen audio content. It adds a host of new features and capabilities that extend the boundaries of what’s possible in digital audio delivery. Some of the most important and exciting of these new benefits include:

Revolutionary efficiency
The first thing people care about with a codec is efficiency, and on that score Dolby AC-4 is revolutionary. While AC-3 delivers 5.1-surround sound at 384 kilobits/second, AC-4 delivers 5.1-surround sound at bit rates as low as 96 kilobits/second. That means AC-4 is up to four times as efficient as AC-3, freeing bandwidth for broadcasters to deliver new premium audio and video experiences.

Solving loudness issues
Dolby AC-4 adds two new technologies, an integrated Real-Time Loudness Leveler and Intelligent Loudness metadata, to solve long-standing loudness issues for file-based and linear content. With these two new systems, content creators can be assured that their artistic intent will be preserved through the entire broadcast chain, while consumers can “set and forget” their device volume in the home. These systems also allow broadcasters to optimize loudness and dynamic range for mobile devices to provide a high-quality and consistent experience.

Enhancing dialogue clarity
One of the key complaints many voice about broadcast today is that dialogue can sometimes be virtually unintelligible. Dolby AC-4 adds an integrated, dual-ended dialogue enhancement feature that enables consumers to increase the clarity of the dialogue, even with older, previously recorded stereo and surround content.

Improving content accessibility
Dolby AC-4 improves content accessibility for viewers who are hearing and visually impaired, and provides a better experience for non-native language speaking audiences. AC-4 allows broadcasters to deliver premium audio mixes in multiple languages, and descriptive audio for visually impaired consumers in less space than ever before.

Driving immersive experiences
Dolby AC-4 delivers Dolby Atmos® immersive audio experiences that create the sensation of sound coming from overhead and all around the consumer. Dolby AC-4 extends the value of Dolby Atmos to mobile devices by providing a high-quality immersive experience at extremely low bit rates for headphones and mobile device speakers.

Personalizing content delivery
Dolby AC-4 offers content owners unprecedented opportunities for delivering personalized audio experiences. Viewers have the power to customize their audio; for example, they can hear a broadcast in an alternate language, listen to a sports team’s local broadcast while watching it on a national network broadcast, or hear a director’s commentary on a favorite movie. Viewers can change the balance between the dialogue and the ambience to improve intelligibility, or crank up the sound of the stadium to be immersed in the action.

Compare the past and future of next-generation audio.

Dolby AC-3 (Dolby Digital)

  • Efficiency
    • Delivers 5.1-surround sound at 384kbps
  • Loudness Management
    • Loudness must be adjusted manually by broadcaster or viewer
  • Dialog Enhancement
    • No dialog control
  • Content Accessibility
    • Limited capability to offer visual descriptive track with real surround sound
    • Limited language options
  • Audio Experience
    • Delivers 5.1-surround sound
  • Personalizing Content Delivery
    • Single experience delivered per stream

Dolby AC-4

  • Efficiency
    • Delivers 5.1-surround sound at 96kbps (4x more efficient)
  • Loudness Management
    • Integrated Real-Time Loudness Leveler and Intelligent Loudness Metadata automatically fix common loudness issues
    • Optimizes loudness and dynamic range for mobile devices
  • Dialog Enhancement
    • Intelligent dual-ended dialog enhancement feature gives consumers control of dialog intelligibility
  • Content Accessibility
    • Multiple presentations provide rich options for visually impaired audiences and enhances multi-language delivery
  • Audio Experience
    • Delivers Dolby Atmos immersive sound experience on headphones, mobile device speakers, soundbars, and home theater systems
  • Personalizing Content Delivery
    • Delivers personalized audio experiences across the whole broadcast and streaming spectrum, including sports, episodic content, documentaries, and live entertainment