|The Science of Domestic Concert Hall Design|
by Ralph Glasgal
Tri-play Recording for Stereo, ITU 5.1/6.1 2D, and Periphonic 3D (with
Height) Compatible Surround Sound Reproduction
at the 115th Convention
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Objectives: Take the next step toward replicating human hearing AND make better recordings in 5.1. In life, we hear sources we see - but also reflections and reverberation we don't see. Each sonic arrival is individually direction-stamped by our unique HRTF, including height, tonally colored by our pinna. Preserving 3D directionality is key to life-like hearing. A practical, scalable approach is presented plus a way to transform 3D (full sphere) recordings for uncompromised 2D reproduction in stereo or 5.1/6.1 without any decoding. By adding a decoder and speakers, full 3D is losslessly reconstituted from 6-channel media. Experimental tri-play 6-channel PerAmbio 3D/2D recordings have been made and demonstrations presented (AES 114th Amsterdam 3/2003 & AES 24th Banff 6/2003) with praised results.
1. EVOLVING REALISM FOR MUSIC & MOVIES
Just as monaural sound reproduction had finally to yield to stereo and stereo to 5.1, so two-dimensional (2D) surround in the horizontal plane will progress toward life-like 3D (with height). In essence, the more the directionality of sound is preserved in 3-space, the more natural the result, as determined by our unique HRTF.
However to date, recording practice in 5.1, like stereo, favors spaciousness and simulating timbre (tonality) at the price of accurate localization - as though mutually exclusive [1, 2, 3, 4, 5]. Progress is needed to realize all three, as in real life. A new system [6, 7] from microphones to media to speakers, PerAmbio 3D/2D, takes a step toward life-like 3D sound with correct spatial impression, timbre AND localization, and that plays compatibly in stereo, 5.1/6.1, 2D, and full 3D using available 6-channel media and 10 or more speakers in a home theater or height-modified cinema.
2. GOALS: COMMERCIAL & ARCHIVAL
Musicians, record labels, and home theater owners have much to gain from lifelike 3D reproduction that is compatible with well-accepted stereo and 5.1/6.1 :
For music-only, these objectives translate into future value to musicians, producers, hardware manufacturers, and consumers - deliverable today on DVD-A, SACD, and DTS-ES. Discrete, CD, and DVD-V movies could also provide an alternate mix in PerAmbio 3D (DTS-ES 6.1 or Discrete). Other applications for 3D reproduction are
3. HISTORY, HEARING, & HEIGHT
Human hearing is unique to us as individuals due to our own HRTF (head-related transfer function), learned at an early age, re-learned after trauma or loss with age, and thus difficult to generalize with auralization. In acoustic spaces, hearing is bound by perceptions called psychoacoustics. Musicians, who "play acoustics" as extensions of their instruments, and recordists are likely to be most sensitive; consumers can learn to be.
When stereo caught on in the 1950s, the author recalls that musicians often favored monaural. Why? Described as the "stage door" effect, mono sounded correct tonally AND was localized at a point in 2D for coming through a narrow opening in the orchestra shell wall. The "sweet spot" included the entire stage wing. Mono sounded like live listening backstage
On-stage, stereo fell short of localizing instruments, as Blumlein himself knew in the 1930s, bunching the panorama of sounds at the speakers (the "hole in the middle") and confusing the pinna about important central soloists, because their sound was coming from speakers far from center. Add that ambience was redirected to frontal speakers, far from around and behind. But consumers, therefore producers, cared more that it sounded spacious. Acoustic music recordists (classical, jazz, folk, etc.) adapted by choosing to get the timbre correct and the "sweet area" large by using spaced omnidirectional microphones in various layouts. More accurate but less spacious sounding coincident M-S 2D and Ambisonic 3D approaches were less successful.
ITU 5.1/6.1 surround sound (2D) extends stereo to try to better envelop listeners, but only partially horizontally, lacking height (3D) and therefore not fully realizing the illusion of live human hearing. New research into surround sound such as 2D Wavefield Synthesis (WFS) and 3D High Order Ambisonics (HOA) are important work and the author finds such demonstrations impressive and their potential great. However, their application to home theater may wait for resolution of impracticalities such as large numbers of high quality microphones, channels, speakers, higher noise, limited frequency range, etc.