Dear friends, this is what we're doing in Muir Woods. Your comments
will be appreciated.
-Dan Dugan
Recording Protocol for Soundscape Monitoring
Version 2.0 (Draft)
This is an attempt to set standards for audio recording in
conjunction with attended soundscape monitoring, so that the work of
different recordists will be comparable.
Format
Stereo digital audio.
Microphones
Type: condensor.
Frequency response: at least 40Hz to 16KHz
Equivalent noise: lower than 25 dBA (signal to noise 69 dB or better).
Effective windscreens are essential. Manufacturer-provided
foam windscreens are inadequate for outdoor work. Good windscreens
can be home-made.
Shockmounts are highly desirable, especially if hand-held.
Stereo Microphone Arrays (listed in the order of preference, best first)
A: Spaced omnidirectional mics with barrier: Jecklin disc,
shoulder mounts, head-worn quasi-binaural, lavs tied around a tree.
B: ORTF array (cardioids spaced 17cm, splayed at 110 degrees).
C: One-point stereo mic X-Y or M-S.
Highly directional types like shotgun or parabolic dish are
not applicable for soundscape recording.
Recorders
Any digital audio recorder with adequately quiet mic preamps.
MiniDisc, Compact Flash or hard drive are all good. A record level
control with steps is a plus. Some kind of scale on the record gain
control (at least 0-10) is necessary for repeatability.
Recording Level
To establish a starting point, hold the microphone at arms
length, sensitive side facing you. Speak normally to a person near
you. Set the recording gain so that the peaks don't exceed a level of
-5dB on the recorder's meter. This gain will work for quiet
environments. Loud sounds will require lower gains.
Calibration
An affordable scheme for calibrating field recording outfits
is being sought. Here is one proposal:
Terminology: "Recording Gain" is the setting of the recorder.
"Recording Level" is the reading of the recorder's peak meter.
Equipment: A digital audio workstation with speakers, a sound
level meter, the recording outfit to be calibrated.
Procedure:
1) Prepare a stereo track of pink noise. Make the channels
uncorrelated if possible.
2) Filter the track with a high-pass at 200Hz and a low-pass at 2000Hz.
3) Play the track and read the sound level meter while adjusting the
monitor level to 65dBA (slow) at a normal listening position
(measuring position).
4) Place your mic precisely at the measuring position and adjust the
recording gain so that the recorder's peak meter reads -5dB (this is
dBFS, meaning "decibels full-scale").
5) Note your recorder's gain setting. Use this as a standard gain for
recording in quiet places.
6) Make a one-minute recording of this calibration noise. Save it to
calibrate transfers later.
Slates
Each take should have a voice announcement (slate) at the
head or tail including:
Recordist's name
Date
Time
Location
Weather and wind conditions
Microphone(s) model number
Recorder model number
Recorder gain setting
Optional description of the scene and the
sound sources you can identify, observed wildlife behavior.
Monitoring
Recording should always be monitored on headphones except
when doing simultaneous attended logging. Attended logging must be
done with naked ears.
Delivery
Make a CD with a track for each monitoring location. Five
fifteen-minute locations with one-minute slates will just fit on an
80-minute CDR. Write your name, the date and the time-slot on the
disc with a list of tracks.
Tape a Tyvek CD sleeve inside a standard file folder. Write
the slate and track information on the outside of the folder. Put a
code number on the folder tab: YYMMDD-T (year-month-day, time slot;
example 050720-night)
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