Hi again David!
Many thanks yet again for your detailed and educational reply. I suppose at=
67 you'd call me a youngster! There's so much in this last post of yours t=
hat I'll have to go through it slowly, and do a few checks for myself.
I have to say that I'm surprised you use Audacity. With your enormous wealt=
h of past experience, there has to be a very good reason that you don't use=
Audition or some such. There was a link to free download of Audition 3 on =
here recently, so it can't be a matter of cost.
Cheers
Max
--- In wrote:
>
> > 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 woul=
d
> 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 pe=
ak
> 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=
like to see active sounds on a spectrogram above my ears' HF cutoff." Is t=
his just pure perversion, in regards the inability to hear these sounds, or=
something else?
>
> Age, pure and simple, but I am known to brag about my residual hearing at=
> 72. :-)
>
> > To me, these ghost sounds are pure frustration! How I'd love to be able=
to hear them. I see beautiful, clear spectrograms of birdsong that I can't=
hear; 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, b=
ut
> if you want to check them out, listen to the recording at half speed. Thi=
s
> 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 m=
ic
> is good enough. It shows up on a power spectrum as an HF tip-up above aro=
und
> 10K. 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 b=
at
> 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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