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Re: [Nature Recordists] Re: Responses to ambient sound recording

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Subject: Re: [Nature Recordists] Re: Responses to ambient sound recording
From: Rob Danielson <>
At 5:06 AM -0500 11/27/10, Dan Dugan wrote:
>
>Raimund wrote,
>
>>  I would suggest to use the sound level meter only for calibrating
>>your microphone and the recorder. You could for instance record a 1
>>kHz test signal through a cheap speaker and record it at a
>>well-defined distance and then measure the sound level by using the
>>sound level meter at the same distance. You would then know the
>>absolute sound level of the recorded 1 kHz test signal as well as
>>the level of the noise that you record at the same gain setting. In
>>this case it would be of course sufficient to have a simple sound
>>level meter with a limited frequency range.
>
>Correct in concept but one has to be very careful in using a tone.
>I've tried it with 1 kHz, and found that if I hand-held the meter
>the reflection from my body will change the reading up or down as
>much as 2 dB. I suggest using band-limited pink noise, 200 Hz to 2
>kHz, for the stimulus, at a level of 64 dBA (slow) measured by the
>sound level meter at the mic location, the SLM on your field mic
>stand at the height you use. Then put the capsule in the same spot,
>with field windscreen, and the recorder set to a precisely
>repeatable record gain.
>
>>  The final noise measurements could then be carried out directly on
>>the recorded .wav files.
>
>Using an A-weighted software meter for the level calibration.
>
>>  This would also allow you to determine the spectral distribution
>>of the ambient noise, which may also significantly influence the
>>vocalization parameters of the singing birds. A number of studies
>>have shown that many animal species shift their songs towards
>>higher frequencies in order to avoid masking effects by
>>low-frequency ambient noise.
>
>Third-octave analysis would surely be enough for this purpose, maybe
>even octave analysis to reduce the quantity of data to be compared.
>
>-Dan
>

Please correct/add to as necessary:

(A) Outside,  at 6' above open ground, play band-limited pink noise,
200 Hz to 2 kHz form a speaker so it reads 64 dBA on a SLM at _______
ft distance

(B) Set your mics/recorder at a usual, repeatable record level
setting in the same spot where the meter was and record the same pink
noise.

(C) Play the recording on your editing app and use A weighted
measurement to determine the dBA reading the 64 dBA stimulus produced.

(D) With this number you can perform simple math. For example, if the
pink noise measures -20 dB with A weighting in your DAW, this means
-20 dBA is equal to 64 dBA. So a quiet location recording with a 30
dBA ambient sound level should read as -54 dBA  [-20 dBA minus 34 dBA
(64-30) ] when read using A weighting in your DAW.

Rob D.

=3D =3D =3D =3D

If any one does this, please share the specifics with us. Rob D.

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