Where a sound comes from is part of what it means.

The neuroscience

A published NIH-indexed study on sound-elevation encoding documented dedicated neural architecture in the auditory cortex for processing vertical position of sound sources. The brain treats “where vertically” as a distinct and specific computation — not an afterthought of horizontal localization. The information about whether a sound originates above, level, or below the listener goes somewhere meaningful neurologically.

This is a real, measurable capacity, not a folk observation. The auditory system is performing elevation computation continuously, and the output is feeding into emotional and threat-assessment circuits.

Horizontal sound and the predator channel

Predators that threatened early humans came primarily from the horizontal plane — ground level. Large cats, other primates, hostile humans. The sounds associated with mortal danger are predominantly horizontal-plane or approaching-from-the-horizontal sounds.

The “looming sound” research confirms this directly: a sound growing louder and closer along the horizontal triggers the strongest threat response in the brain. The midbrain defense circuits — the ancient threat-detection architecture — fire hardest for sounds that behave like an approaching ground-level threat. This is not a learned response; it is built into the wiring.

Overhead sound and the canopy channel

Birdsong, by contrast, comes from above. Trees, sky, canopy. The nervous system has been calibrated for millions of years to associate overhead sound with the canopy being occupied and safe, not with ground-level danger approaching.

There is a reason birds going silent overhead is alarming and birds singing overhead is not. The elevation itself carries information. The canopy speaking back is the environment confirming itself.

Two-channel model

Combining the above, the nervous system has at least two distinct default readings of acoustic elevation:

Direction	Default reading	Examples
Horizontal / approaching	Threat channel — caution, attention, possibly fight-or-flight	Footsteps approaching, vehicle approaching, voices closing in
Overhead / canopy	Environment channel — the world above is occupied, things are normal	Birdsong, wind through high branches, rustling leaves
Below / underground	Ambiguous — historically rare, often anomalous	Rumbles, basement noise

The two-channel model is not absolute — context overrides default readings often. But the defaults are real, measurable, and built into ancient neural circuits.

The thunder exception

Thunder is the natural exception that proves the rule. Thunder comes from overhead, but it is not a safety signal — it is a warning signal. The body processes thunder as legitimate large-scale atmospheric energy with the potential for danger (lightning strike, severe weather). The reading is: something significant is happening above; take shelter.

This is why thunder produces a distinctive nervous-system response that is neither the relaxed canopy reading nor the alerted ground-predator reading. It is its own category — overhead-but-serious.

Aircraft noise hijacks the thunder channel

Aircraft noise from flight paths plugs into the thunder channel. Aircraft produce significant low-frequency content and infrasound — they share the overhead, low-frequency, large-scale profile of natural thunder.

The midbrain reads it through the channel built for thunder: something large and potentially dangerous is happening above. But unlike thunder, which is rare and finishes, aircraft noise under a flight path is rhythmic, regular, and never-ending. The thunder channel never gets to close. The body stays in a chronic anticipatory state about overhead atmospheric energy.

See Aircraft for the full treatment of cardiovascular and sleep damage from chronic flight-path exposure.

Practical implication for birdsong broadcast

If urban environments are going to broadcast birdsong as a stress-mitigation strategy (see Birdsong), overhead placement is biologically more accurate than ground-level placement.

• Building-top speakers
• Elevated installations in plazas and parks
• Mounted on trees or canopy structures rather than at standing height

Ground-level speakers playing birdsong still work — the signal content carries the safety reading regardless of source — but overhead placement reproduces the natural elevation signature the nervous system evolved expecting. The biological reading is cleaner.

Practical implication for noise abatement

The reverse implication is also worth naming. Loud machinery operated at ground level (mowers, blowers) is read primarily through the horizontal/threat channel. Loud overhead noise (aircraft, drones) is read primarily through the canopy/thunder channel.

Both are damaging — see Health and Aircraft — but the mechanism of damage is partially different. Ground-level noise drives chronic horizontal-threat arousal. Overhead noise drives chronic thunder-channel arousal. Effective mitigation may differ between the two cases:

• For ground-level industrial sound: noise abatement at the source, distance, barriers.
• For overhead aircraft sound: routing changes, altitude minimums, fleet quieting, and attention to whether the body’s thunder-channel arousal can be partially offset by deliberate overhead positive signals (canopy birdsong, gentle wind chimes).

Connection to wind chimes

The fact that wind chimes are traditionally hung overhead — under eaves, from trees, from porch ceilings — is not aesthetic only. Chimes occupy the same elevation channel as birdsong and natural wind-through-canopy. They feed the safe-overhead reading. See Wind chimes.