Dolby Atmos Home Theater: Unveiling the Facts with a Star Wars Mixing Engineer

Audioholics

Introduction [0:00]

The video features a discussion with John Traunwieser, a renowned recording and mixing engineer for film and TV, known for his work on productions like Star Wars and The Hunger Games. The discussion aims to clarify confusion and misinformation surrounding Dolby Atmos, speaker placement, and mixing practices.

Dolby Atmos Standards and Mixing Formats [1:49]

• Primary Formats: Dolby Atmos is the primary standard for cinematic and home entertainment mixes.
  • DTS:X and IMAX are also present but receive less attention.
  • Auro 3D is rarely used for mixing.
• Mixing Workflow:
  • Some projects start with a 5.1 or 7.1 mix, then up-mix to Atmos, especially if budget-driven.
  • More often, the Atmos mix is created first, then down-mixed to other formats (e.g., 7.1, 5.1, stereo).
• Theatrical vs. Near-field Mixes:
  • Theatrical mixes are distinct from near-field (home) mixes due to differences in room size and speaker configurations.
  • Near-field mixes for streaming platforms are sometimes prioritized, with theatrical versions being adapted later for archival or delayed release.

Gold Standard Atmos Layout for Home [4:50]

• Recommended Home Setup: The near-field standard for Dolby Atmos in homes is 7.1.4.
  • While 7.1.2 is the Atmos bed, adding more speakers (up to 7.1.4) takes advantage of object-based audio for enhanced immersion.
  • Having four height channels offers distinct advantages over two for more precise object localization and an immersive experience.
• Objects in Atmos:
  • Objects are primarily used for:
    • Atmospheric sounds to fill the space.
    • Point-source sound effects (e.g., whizzing sounds) for better localization.
  • Music soundtracks are typically not heavily object-based, as instruments are not intended to "fly around the room." Exceptions include using height channels for choir to create a sense of scale.
  • In streaming media, object tracks have a lower bitrate than bed channels, which can impact sound quality if used for critical music elements.

Height Channel Guidelines [16:00]

• Studio vs. Home Spec:
  • Theatrical Atmos specifications often place height channels closer to the center of the room.
  • Home entertainment Atmos specifications tend to recommend wider placement of height channels.
  • John Traunwieser, as a mixer, prefers height channels closer to the center to maintain isolation and separation from ear-level speakers, ensuring clearer localization of sounds from above and around.
• Personal Preference for Placement: Some installers, like the video host, prefer a narrower angle for front and rear height speakers (e.g., 25-30 degrees forward and backward) to enhance immersion, even if it deviates from Dolby's wider recommendations.

Psychoacoustics of Elevated Sound [34:48]

• Perceiving Sound Horizontally (Azimuth): Relies on interaural time difference (ITD) and interaural level difference (ILD), allowing for accurate localization (less than 2 degrees error).
• Perceiving Sound Vertically (Elevation): Is more complex and less accurate than horizontal panning.
  • Primarily relies on visual cues and Head-Related Transfer Functions (HRTF), which are changes in spectral balance as sound moves vertically.
  • Without visual cues, people are poor at vertical localization (often 10-20 degrees off target).
  • Virtual panning between speakers (where no actual source exists) can create inaccuracies as the brain doesn't receive the correct HRTF shifts.
• Depth Cues: The perception of depth, such as distinguishing nearby from distant sounds, is influenced by the direct-to-reverberant sound ratio and visual cues. Mixers use these nuances to create a virtual world with depth and distance.

Atmos Placement Takeaways [47:57]

• Speaker Location is Critical: Adhering to recommended angles, within practical limits, is crucial for accurate sound reproduction.
  • Professionals can navigate room obstacles and make informed placement decisions.
• Separation is Key: Speakers placed too close together hinder sound separation, making panning ineffective.
• Wide Channels (Wides): Some engineers use wides, but John Traunwieser generally avoids them due to concerns about object data bitrate compression and potential phasing issues during down-mixing.

Streaming vs. Hard Disc [1:08:13]

• Bitrate Differences: Streaming services (e.g., Apple TV, Netflix) use lower bitrates, impacting the quality of both bed channels and object tracks.
  • Hard disk playback (e.g., Kaleidescape) offers significantly superior audio fidelity due to uncompressed or less compressed audio.
• Device-Specific Calibrations: Different playback devices (e.g., Kaleidescape vs. Apple TV) may require separate calibrations for optimal sound, as they can author content differently, affecting levels and frequency response, especially in the low end.

The Last Jedi Sound [1:13:19]

• Budget and Time Constraints: Even high-budget films like Star Wars face budget and time limitations, which can impact the final mix.
  • Audio is typically the last stage of post-production, often rushed to meet release dates.
• Filmmaker Input: Director and producer feedback, including test screenings with random audiences, can lead to last-minute changes that may or may not improve the overall mix.
• Monitoring Levels: The standard monitoring level for theatrical mixing is 85 dB, but for TV it can be 80 dB. Playing content at lower levels can significantly reduce emotional impact, especially if the music (which is often mixed quietly) is central to the film's emotion.
• Music Loudness: Music in films is often mixed very quietly. A global increase of 3 dB in music levels could restore the intended emotional impact for audiences.

LF Bass Truncated in Atmos Mixes? [1:21:27]

• Low-Frequency Content: Mixers sometimes use high-pass filters on low-end frequencies to protect consumer speakers and avoid distortion, especially for home entertainment releases.
  • However, for impactful sound effects like explosions, the deep low end (below 30 Hz) is desirable for immersive experiences.
• Infrasonic Subwoofers: The use of very large infrasonic subwoofers (playing below 20 Hz) is a growing trend in home theater.
  • Professional studios generally use multiple, smaller subwoofers for controlled, high-SPL low-end reproduction, avoiding distortion.
  • Decisions on low-end treatment are often at the mixer's discretion, and sometimes influenced by notes from studio executives or filmmakers.

In-Ceiling or On-Wall for Heights? [1:38:00]

• Professional Standard: Virtually all professional mixing studios use in-ceiling speakers for Dolby Atmos height channels.
• On-Wall Placement: Can be acceptable in specific scenarios (e.g., very low ceilings) if the correct angles are maintained. However, it's generally not the preferred position.
• Up-firing Speakers and Soundbars: These consumer-oriented solutions are generally not recommended for true Atmos experiences, as they rely on sound bouncing off surfaces, leading to unpredictable and distracting results that deviate significantly from the mixed intent. John considers this an "abuse of terminology."

Benefits of Pro Calibration [1:44:44]

• Importance of Calibration: Professional calibration is crucial for achieving accurate sound reproduction that aligns with the artist's intent.
  • Auto-calibration systems in consumer receivers are often inadequate and provide poor results.
• Reference Point: A properly calibrated room provides a consistent reference point for mixing and playback. Without it, engineers cannot accurately judge their mixes.
• Calibrator Expertise: The quality of calibration can vary significantly depending on the calibrator's expertise. Specialized calibrators are needed for film vs. music.
• Acoustic Treatment: Professional mixing studios require carefully designed acoustic treatment to create a "dead" room environment, minimizing room reflections so the engineer hears only the mix itself, not room coloration. This differs from a typical home theater where some controlled reflections contribute to a sense of spaciousness.

Skywalker Sound [1:54:00]

• Iconic Facility: Skywalker Sound is a renowned facility where many major films, including Star Wars, are mixed and recorded.
• Equipment: They use Meyer Sound cinema speakers, similar to those found in other major studios like Fox and Sony.
• Scoring Stage: Skywalker Sound also boasts a large scoring stage where orchestras can record music for films.
• Historical Recordings: Older music recordings (e.g., Pink Floyd, Beatles, Queen) were often done with discrete multi-track analog equipment, allowing for high-quality restoration and re-mixing into modern formats like Atmos, resulting in surprisingly good sound quality.