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Field Recording Protocol

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Alexander Refsum Jensenius edited this page Jul 17, 2026 · 3 revisions

The two-minute discipline that makes a session analyzable without detective work. Distilled from sessions where each item below was, at some point, learned the hard way.

Equipment & settings (keep constant)

  • Zoom H3-VR (or comparable FOA recorder), AmbiX record mode, Upright position, correction filter off, 24-bit / 48 kHz.
  • Note which B-format convention the recorder writes (AmbiX vs FuMa) — ambiscape auto-detects from the BWF zTRK tags, but downstream tools may not. A convention mixup silently wrecks all directional analysis.
  • Check the recorder clock against your phone monthly. Clock drift of tens of seconds is invisible until you try to align with the outside world (train timetables, church clocks, other sensors).

At every setup (~2 minutes)

  1. Orient — tape arrow on the recorder marks X+ (front); note its compass bearing (phone flat, aligned with the arrow).
  2. Photograph the setup from above — doubles as a position record.
  3. Clock sync — photograph the recorder screen next to the phone clock, or speak the phone time into the first seconds.
  4. Calibration claps — snap or clap once from 2–3 known positions (window, door, dominant machine) in a noted order: direction ground truth inside the recording, immune to lost notes.
  5. Room impulse — one balloon pop (or loud clap) ≥ 2 m from the mic with 5 s of stillness before and after → clean T60 via ambiscape.analysis.decay_time. Movement immediately after a clap truncates the usable decay to a fraction of a second.

Session notes (5 lines, in the session folder)

place:    <city, building, room>
position: <mic location; height; X+ bearing ° magnetic>
time:     <timezone; recorder-vs-phone offset s>
state:    <windows; HVAC/machines on-off + any toggles you make>
context:  <weather; who is present; expected sources>

Stage transitions deliberately

Toggling a machine (ventilation off for ten minutes, fridge unplugged for an hour, window opened) is the cheapest acoustic experiment there is: the transition separates source from room, reveals what the steady state masks, and gives every analysis a labeled event. Note the exact time of every toggle.

If absolute SPL matters

One SPL-meter reading of a steady source (running HVAC is perfect) next to the mic, noted with the session → a calibration.json that converts the whole session from dBFS to dB SPL.

Optional: ISO 12913 self-report

One minute at the recorder rating the eight perceived affective qualities (pleasant, vibrant, eventful, chaotic, annoying, monotonous, uneventful, calm) gives each session a genuine ISO 12913-2 Method-A perceptual data point — the layer no instrument can supply.

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