Raimund wrote,
> I would suggest to use the sound level meter only for calibrating your m=
icrophone and the recorder. You could for instance record a 1 kHz test sign=
al through a cheap speaker and record it at a well-defined distance and the=
n measure the sound level by using the sound level meter at the same distan=
ce. 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 sou=
nd level meter with a limited frequency range.
Correct in concept but one has to be very careful in using a tone. I've tri=
ed it with 1 kHz, and found that if I hand-held the meter the reflection fr=
om my body will change the reading up or down as much as 2 dB. I suggest us=
ing 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 re=
corded .wav files.
Using an A-weighted software meter for the level calibration.
> This would also allow you to determine the spectral distribution of the a=
mbient noise, which may also significantly influence the vocalization param=
eters of the singing birds. A number of studies have shown that many animal=
species shift their songs towards higher frequencies in order to avoid mas=
king effects by low-frequency ambient noise.
Third-octave analysis would surely be enough for this purpose, maybe even o=
ctave analysis to reduce the quantity of data to be compared.
-Dan
|