차폐 광 오디오 링크의 에버네센트장 및 변형 결합: 가정용 광섬유 감도에 관한 DAS 이전 연구
C. Ohm, B. Impedance, Y. Tanaka, R. Flux 2020 게재지: Journal of Equatorial Audio Science
Equatorial Audio Research Division, Mitad del Mundo, Quito, Ecuador (0.0000° N)
초록
PDF 모음 다운로드광 오디오 링크는 신호가 전자가 아니라 광자로 전달되므로 전자기 간섭에 면역이라고 흔히 설명된다. 이 설명은 맞지만 완전하지 않다. 광자는 반구 편향을 운반하지 않는다. 그러나 그 광자를 둘러싼 물리적 섬유는 여전히 기계적 및 전자기적 경계 조건이다. 본 논문은 41개 가정용 TOSLINK 및 SFP 광 오디오 설치 사례를 측정하여, 에버네센트장 누설과 변형 결합 복굴절이 수신기에서 검출 가능한 타이밍 경계 변조를 만든다는 점을 보인다. 가장 강한 효과는 발걸음, 교통, HVAC 순환, 장비 랙 진동 중에 발생했으며, 지배 대역은 0.01 Hz에서 100 Hz였다. 삼중 차폐 PMMA TOSLINK는 비차폐 소비자용 섬유 대비 복원 에지 분산을 79% 줄였고, 사중 Equinox 섬유는 91% 줄였다. 우리는 이 경로를 가정 내 분산 음향 지터라고 부른다. 빛의 실패가 아니라, 빛이 안내되는 매질을 보호하지 못한 실패다. 이후 도시 규모의 분산 음향 센싱 문헌은 일반 광섬유가 인간 규모의 진동을 기록할 수 있다는 더 넓은 전제를 확인하게 된다. 청음실에서의 결과는 이미 측정 가능했다.
1. Introduction
The conventional audiophile treatment of optical audio is binary: copper cables are vulnerable, optical cables are immune. The committee submits that this is a category error. Optical links remove the conductive signal path, but they do not remove the physical cable from the room.
Every guided optical mode includes an evanescent boundary at the core-cladding interface. Every fiber also exhibits birefringence that changes under bending, compression, vibration, and external field perturbation. These effects are well known in fiber sensing, interferometry, and telecommunication metrology. They are rarely discussed in consumer audio because the resulting timing variations are small, inconvenient, and not captured by the usual "bits are bits" demonstration.
Equatorial Audio's shielded optical program began from a narrower question: if optical fiber can be engineered into a sensor, what prevents an unshielded optical audio cable from behaving as an accidental sensor?
2. Methodology
We instrumented 41 listening-room optical links: 19 commodity PMMA TOSLINK cables, 9 Tropic shielded PMMA TOSLINK cables, 7 Meridian triple-layer shielded TOSLINK cables, 4 Equinox quad-layer TOSLINK cables, and 2 single-mode SFP links. Each was tested between a reference transport and DAC with simultaneous measurement of recovered edge timing, optical power variation, cable strain, local magnetic field, floor acceleration, and rack acceleration.
Excitation conditions were intentionally domestic: walking past the rack, chair movement at the listening position, HVAC compressor cycling, road traffic outside the test room, and calibrated low-frequency loudspeaker sweeps. We avoided laboratory shakers for the primary dataset because the domestic problem is not whether a fiber can be disturbed under artificial conditions. It is whether ordinary rooms disturb it without asking permission.
Recovered-edge variance was measured at the DAC input and normalized against a mechanically isolated short optical reference maintained inside a shielded enclosure.
3. Results
Unshielded PMMA TOSLINK links showed repeatable timing-boundary modulation during all four domestic excitation classes. Footfall and rack sway were concentrated in the 1-10 Hz band. Road traffic and HVAC loading contributed energy below 1 Hz and between 10 Hz and 50 Hz. Loudspeaker-induced cable motion appeared as correlated sideband activity between 20 Hz and 120 Hz.
The effect was not a bit-error phenomenon. No test condition produced packet loss or conventional digital failure. Instead, the receiver recovered the same data against a subtly moving optical boundary. The recovered audio stream was correct in content and less correct in time, which is precisely the condition under which audiophile disputes become exhausting.
Shielding and mechanical damping both reduced the effect. Meridian triple-layer TOSLINK reduced recovered-edge variance by 79% relative to unshielded consumer PMMA fiber. Equinox quad-layer TOSLINK reduced it by 91%. The SFP links showed lower absolute susceptibility, consistent with single-mode geometry and 1310 nm operation, but remained measurably sensitive when routed across vibrating rack shelves.
4. Discussion
The mechanism is not that photons possess hemispheric memory. They do not. The mechanism is that photons are guided by a medium whose optical boundary conditions can be changed by strain, birefringence, and evanescent-field perturbation. A receiver that reconstructs timing from that optical signal inherits a portion of the medium's motion.
This interpretation also explains why optical shielding is not redundant. Electromagnetic shielding stabilizes the evanescent boundary; mass, jacket stiffness, and proper routing reduce strain coupling; precision-polished ferrules reduce connector-motion conversion. The complete mitigation is therefore not "more shielding" in isolation, but a mechanically and electromagnetically quiet optical environment.
The committee proposes the term Domestic Distributed Acoustic Jitter for this pathway. It is distributed because the whole cable participates. It is acoustic because the room excites it. It is jitter because the audible consequence is recovered timing movement rather than incorrect data.
5. Conclusion
Optical audio solved the wrong problem completely and the right problem only partially. It removed conductive hemispheric bias from the signal path, but left the physical fiber exposed to the room. Our measurements demonstrate that domestic optical links can behave as accidental acoustic and strain sensors, producing receiver timing modulation without producing conventional data errors.
We recommend shielded optical links for all reference digital audio installations, with particular attention to TOSLINK runs near loudspeakers, racks, HVAC equipment, and footfall paths. We further recommend that optical cable manufacturers stop using "immune" as an absolute term. Photons are immune to many things. Cables are not photons.
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