> David, I don't know what you mean by a power spectrum; please explain.
Max,
It's a graph of the power in dBs against frequency. Pure white noise would=
give a horizontal line, pink noise a line sloping down left to right and
blue noise the other way. It also can be a useful tool to identify the peak=
frequency of a sound like a tweet in a selected section of the recording.
> The next thing about your reply that intrigued me was, to quote "I also l=
ike to see active sounds on a spectrogram above my ears' HF cutoff." Is thi=
s just pure perversion, in regards the inability to hear these sounds, or s=
omething else?
Age, pure and simple, but I am known to brag about my residual hearing at
Message: 72.
Subject: :-)
> To me, these ghost sounds are pure frustration! How I'd love to be able t=
o hear them. I see beautiful, clear spectrograms of birdsong that I can't h=
ear; brrrrr! The last time I checked, my HF cut-off was around 9K
That's not bad. You are only missing part of the upper octave. Some high
pitched birds will sound lower in level, and harmonics will be missing, but=
if you want to check them out, listen to the recording at half speed. This=
will also reveal HF noise which will have probably shown up on the power
spectrum.
With a very quiet background or using my mic hiss test under a pile of
bedclothes, you can see the fundamental thermal noise of the air if the mic=
is good enough. It shows up on a power spectrum as an HF tip-up above aroun=
d
Message: 10K.
Subject: To hear it as well, listen as a quarter speed.
I've seen inaudible sounds on a spectrogram which turned out to be mammal
squeaks. I use bat detectors and these also show up inaudible crickets.
There is a whole world of ultrasound we are normally not aware of. Last
night I was tracking Lesser Horseshoe bats at around 110KHz. Our lowest bat=
calls here are 17Khz and I've picked them up on straight audio recordings.=
The best human ears miss quite a lot of birdsong components.
I use the free Audacity editor and it has power spectrum and spectrogram
functions, speed changes and a lot more.
David Brinicombe
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