[ProAudio] Calibrated playback level

[Dan Dugan]

David Josephson, you wrote,
> We (and NASA, and some others) are making libraries of ambient soundscape recordings to demonstrate what these things sound like in different neighborhoods. Each ambient includes a 94 dB SPL 1 kHz tone, which gets replaced with 500-2000 Hz filtered pink noise of the same rms level. That’s scaled to play back in the listening space at 94 dB, all speakers operating.

For many years I’ve tried to calibrate my nature recording channels to 0dBFS = 70dBA SPL. That will handle 99.99% of environmental sounds. Exceptions have been thunder, Pacific chorus frogs nearby, and Osprey tilt-rotor aircraft. I do the channel calibration in a diffuse field (10 speakers) at 64dBA = -6dBFS, pink noise filtered 200-2000Hz, windscreens on.

For species reporting study, and for aesthetic enjoyment, I monitor in the field and listen in the studio a lot louder than the natural level. This is for the same reason that birders look at birds through at least 8x (like 18dB?) binoculars. To extend the senses into the distance, to discern detail the naked eye/ear cannot.

I want to develop a field calibrator for use with mic arrays with windscreens in place. Imagine a smartphone holder with a 1/2-meter telescoping probe that is touched to the outside of the windscreen assembly. The operator selects a pre-set channel, mic type, and angle of approach (think about a single windscreen containing M/S or ambisonic elements). The calibrator speaks the name of the channel and the angle, sends it in modem tones, and plays a burst of band-limited noise. Using a smartphone, the test noise is mainly high-frequency but that’s good, because at lower frequencies reflections from the operator’s body are significant—like 1.5 dB at 1K.

-Dan