Very interesting.
My obs:
Shift or "width" increase of the lower band mosquito din is around 60-70 Hz=
.
Eyeballing the FFT there doesn't seem to be any low frequency vibration sug=
gesting mic movement, nor a shift of frequencies e.g 11hz other than the mo=
squito din after Hans speaks. Other vocalisations present also do not affec=
t the mosquito frequency change. The decay is around 2.5 seconds. The effec=
t I assume is due to localized heating of the air volume and change of humi=
dity near the mic. The signal (mosquitoes) seems to widen or shift (shift i=
s perhaps not ideal) by 60-70 hz for the lower band, higher up its more pro=
nounced tending to blends with its neighbor harmonic. Thus the original fr=
equency bands are expanding width / higher during the speech. The speed of =
sound increases with temperature, if the mic is close to Hans the localized=
heating / moisture may account for the effect.
http://www.rane.com/pdf/eespeed.pdf
If we assume humidity to be 100% after speaking and its 20 C and 50% humidi=
ty at the recording location it may correspond to 3.98-3.79 =3D 0.19% chang=
e and given the low band being around 372 Hz, thats around 70Hz shift which=
is curiously close to the observed value. But Im just shuffling numbers ar=
ound perhaps theres a more scientific method available to calculate the eff=
ect?
Perhaps one method would be rule out Han's proximity and test / prove this =
strange coupling with a speaker near the mics to confirm the "spooky action=
at a distance".
One thing that puzzled me, is the din folding down from ultrasonic frequenc=
ies to 370,747hz etc or is that where mosquito buzzing normally sits on th=
e spectrogram?
-Mike.
Figures based on decimating the original audio by 8 at 48Khz sample rate.
--- In "rock_scallop" <> w=
rote:
>
> That is interesting, Hans. Were you and the mics both stationary during t=
he test? - just to rule out any relational effects.
>
> John Hartog
> rockscallop.org
>
> --- In "Hans Christian" <hanskock@> wro=
te:
> >
> > Hi all
> >
> > Recently I was out in the Nationalpark Thy in Northern Denmark, to reco=
rd ambiences just after sunset, when I came across an extremely weak hummin=
g-sound. Barely audible without the recorder gain at max. It turned out to =
be hundreds of mosquitoes inside a small forest. I started recording, and t=
hen when I made the announcement into the mic, I noticed the mosquito-hum r=
aising in pitch for a short moment. I made different experiments, and it se=
emed they only reacted to my voice each time, and not any other sounds I ma=
de.
> >
> > Has anyone come across that phenomenon? Is it a known fact that mosquit=
os can "hear" humans, and distinguish them from other sounds? I've never he=
ard of that.
> >
> > I put up the recording on SoundCloud, but it probably requires some goo=
d headphones to hear the phenomenon:
> >
> > http://snd.sc/NqgQhY
> >
> > (I speak to the mosquitoes in danish, but don't bother. I'm not saying =
anything very intelligent anyway. After all, they are only mosquitoes...)
> >
> >
> > Hans Kock
> >
>
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