Rich Peet wrote:
> That is what I thought too. But then I look at the FFT spectral
> display, which in Cooledit goes to 16,384. The display is completing
> the curve down to 1/2 cycle in a short time frame. I don't
> understand how in such a short time frame it is resolving 1/2 cycle.
> Is this bird really calling to 1/2 cycle. Also, this was recorded
> with a me-62 and a consumer minidisc and not my mkh-110-1. The mic
> is rated at 5 cycles and the MD is not rated that I know of which
> means they choose not to lie. Is there such a thing as a sub-
> harmonic?
>
> See my spectral display as a short download at:
> http://home.comcast.net/~richpeet/grouse.jpg
What do you find when you look at the waveform display?
Rather than sub-harmonic, you tend to see modulation of a higher
frequency by the low frequencies in the waveform display. At the 1/2 hz
level those will probably be your most accurate measure.
I'd certainly doubt a me-62 and small MD as giving a true picture at
these low frequencies. Though they will certainly pick up a modulation
as above.
Remember, sonograms also have artifacts, so you would have to figure
out how much was that. You have two things going in a sonogram in how it
calculates that have a big effect on the display you get. First is how
many samples it uses for each step of the FFT, and second is how far it
steps through the samples before making the next round of calculation.
These both change how the display comes out. There is a big tradeoff
between resolving on the time scale and resolving on the frequency
scale. You have to choose what's important for what you are doing.
And that does not even get into how the programmer implemented the FFT
in the computer. And there are probably as many ways for that as there
are programmers.
Walt
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