3-channel parametric stereo image mixer

Compact 3-Channel Ambient Capture Array (Jecklin Disk + Decca-Style Center) Operates as a 3-channel parametric stereo image mixer

1. Overview

Three-microphone array using a ~13-inch Jecklin disk with spaced left/right capsules (9–11 inches) and a discrete center channel. The system is designed for rapid deployment and post-defined imaging.

Left/right channels operate as a wide AB pair with acoustic shadowing, forming the primary spatial image and low-frequency continuity. The center channel functions as a controlled mid-field reinforcement path used to tune the inherent Jecklin midrange “hollow” and adjust perceived width, depth, and center solidity.

The system is intentionally under-committed at capture. Final spatial characteristics are constructed in post.

2. Physical Configuration

• Disk: ~13" diameter absorptive/diffusive baffle
• L/R spacing: 9–11 inches (symmetry within millimeters required)
• L/R height: matched
• Center: on-axis, same height, aligned to disk plane
• Mounting: rigid to maintain phase stability

3. Signal Roles

• L/R (primary pair) Wide AB with acoustic shadowing Defines spatial field, width, and low-frequency structure
• Center (control channel) Non-coincident reinforcement Adjusts mid-field density, localization bias, and depth

4. Capture Method

• Record all channels clean (no processing printed)
• Maintain consistent gain staging
• Center recorded conservatively (approx. 10–14 dB below L/R reference)
• No intentional delay or phase manipulation applied at capture

Capture goal: preserve a flexible spatial dataset, not a finished image.

5. Parametric Image Control (Post)

The system functions as a 3-parameter spatial mixer:

• Center Level → controls width vs center density
• Center Delay → controls arrival priority and depth (precedence weighting)
• Center Spectrum → controls perceptual presence and tonal integration

L/R remain fixed as the spatial reference. Center is introduced incrementally.

6. Center Delay / Haas Positioning

• 0 ms (impulse-aligned) Center dominates; image narrows and pulls forward
• +0.15–0.3 ms (baseline) Center integrates without collapsing width
• +0.3–0.8 ms Center recedes; introduces depth layering
• 1 ms Perceptual detachment or smear

At this scale, sub-millisecond adjustments are audible and significant.

7. Capsule Configurations

Omni L/R + Omni C (neutral fill)

• Maximum coherence and LF continuity
• Soft center; requires higher level
• Best for open outdoor ambiences

Omni L/R + Cardioid C (balanced control)

• Controlled center reinforcement
• Mild tonal seam, stable behavior
• General-purpose configuration

Omni L/R + Hypercardioid C (forward bias)

• Increased center definition and depth
• Rear-lobe contamination possible
• Requires conservative level

Omni L/R + Shotgun C (spot bias)

• Strong forward isolation
• Phase coloration in upper mids
• Stylized or corrective use

Cardioid L/R + Omni C (room control)

• Reduced ambient pickup
• Center restores LF and mid presence
• Suitable for reflective interiors

Cardioid L/R + Cardioid C (fully directional)

• Narrower field, strong front focus
• Tonally consistent
• Risk of flattening if overused

Cardioid L/R + Hyper C (aggressive control)

• Tight, forward image
• Increased coloration
• Limited practical use

Hyper L/R + Omni C (maximum rejection)

• Strong side rejection
• Reduced spatial scale
• Noise-control scenario only

8. Center Omission / Hollow Utilization

The center channel may be reduced or omitted:

• Preserves Jecklin midrange dip
• Creates a natural center “slot”
• Enables clean insertion of mono dialogue or focal elements
• Most effective with omni L/R

9. Dialogue Integration Workflow

• Fade center down gradually (no hard mute)
• Begin fade before dialogue onset
• Restore after dialogue ends
• Maintain L/R unchanged

Result:

• Clear center placement for dialogue
• Stable ambient field
• Minimal corrective processing

10. Operational Constraints

• Sub-millisecond timing sensitivity
• Gain changes of 2–3 dB significantly alter imaging
• Capsule mismatch introduces phase/tonal variance
• System is not phase-coincident
• Imaging is perceptual, not mathematically coherent
• Configurations should remain fixed per session

11. Use Cases

• Outdoor ambiences with adjustable center solidity
• Interior environments requiring room control
• Hybrid production workflows combining ambience and dialogue
• Rapid field recording with post-defined imaging

12. Limitations

• Not mono-compatible in the traditional sense
• Dependent on post-processing decisions
• Requires careful alignment and gain discipline
• Mixed polar patterns introduce tonal discontinuities

13. References

Haas H. Über den Einfluss eines Einfachechos auf die Hörsamkeit von Sprache. Acustica. 1949. https://www.akustik.rwth-aachen.de/global/show_document.asp?id=aaaaaaaaaaxlqjp

Wallach H, Newman EB, Rosenzweig MR. The precedence effect in sound localization. Am J Psychol. 1949. https://psycnet.apa.org/record/1950-03754-001

Blauert J. Spatial Hearing: The Psychophysics of Human Sound Localization. MIT Press. https://mitpress.mit.edu/9780262523454/spatial-hearing/

Rayleigh L. The Theory of Sound. 1907. https://archive.org/details/scientificpapers04raylrich

Jeffress LA. A place theory of sound localization. J Acoust Soc Am. 1948. https://asa.scitation.org/doi/10.1121/1.1906448

Duda RO, Martens WL. Range dependence of the response of a spherical head model. JASA. 1998. https://pubs.aip.org/asa/jasa/article/104/5/3048/570570

Møller H, et al. Binaural technique: Do we need individual recordings? JASA. https://pubs.aip.org/asa/jasa/article/104/4/2181/570321

Williams M. Microphone array analysis for stereo and surround sound recording. AES. https://www.aes.org/e-lib/browse.cfm?elib=6326

Griesinger D. Spaciousness and envelopment in listening rooms. AES. https://www.aes.org/e-lib/browse.cfm?elib=5657

Rumsey F. Spatial Audio. Focal Press. https://www.routledge.com/Spatial-Audio/Rumsey/p/book/9780240516232

Pulkki V. Virtual Sound Source Positioning Using Vector Base Amplitude Panning. JAES. 1997. https://www.aes.org/e-lib/browse.cfm?elib=7853