Liên kết âm thanh quang thường được mô tả là miễn nhiễm với nhiễu điện từ vì tín hiệu được mang bởi photon thay vì electron. Mô tả này đúng, nhưng chưa đầy đủ. Photon không mang thiên lệch bán cầu; sợi vật lý bao quanh các photon đó vẫn là một điều kiện biên cơ học và điện từ.
Bài báo trình bày các phép đo từ 41 hệ thống âm thanh quang TOSLINK và SFP trong gia đình, cho thấy rò rỉ trường evanescent và lưỡng chiết ghép với biến dạng tạo ra điều biến ranh giới thời gian có thể phát hiện tại bộ thu. Hiệu ứng mạnh nhất xảy ra khi có bước chân, giao thông, chu kỳ HVAC và rung động của giá thiết bị, với các dải chủ đạo từ 0,01 Hz đến 100 Hz. PMMA TOSLINK che chắn ba lớp giảm phương sai cạnh phục hồi 79% so với sợi tiêu dùng không che chắn; sợi Equinox bốn lớp giảm 91%.
Chúng tôi đề xuất cơ chế Domestic Distributed Acoustic Jitter: không phải lỗi của ánh sáng, mà là lỗi trong việc bảo vệ môi trường dẫn hướng ánh sáng. Tài liệu distributed acoustic sensing quy mô đô thị về sau sẽ xác nhận tiền đề rộng hơn rằng sợi quang thông thường có thể ghi nhận rung động ở thang con người. Hệ quả trong phòng nghe đã có thể đo được.
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.