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Re: Determining peak frequencies

Subject: Re: Determining peak frequencies
From: "vickipowys" vpowys
Date: Thu Nov 22, 2012 1:56 pm ((PST))
I have been playing around with Aucacity, its Plot Spectrum facility  
seems to do the job very nicely with recordings of my local insects.   
I simply load the sound file directly into Audacity, select 5 seconds  
or less from a strong part of the waveform, then go to Analyze/ Plot  
Spectrum, to find the loudest frequency in that call.

However I would again stress the need to make the original recording  
of insects (especially katydids) with a recording sample rate set  
MUCH HIGHER than 44.1.   96 kHz would be a better bet, and would  
capture insect sounds up to 48 kHz.

Checking in Audacity, I see that my local Whitish Meadow Katydid  
Conocephalus albescens has the loudest part of its call at 30 kHz.   
The Blackish Meadow Katydid is much less at around 18 kHz, while the  
Upolu Meadow Katydid comes in at around 24 kHz.  A grasshopper  
Froggatt's Buzzer has a peak of up to 24 kHz.

Vicki Powys

On 23/11/2012, at 3:55 AM, symmerista wrote:

> David,
> By "peak frequency" the insect folks mean the loudest frequency, I  
> think.
> Audacity seems like a worthy alternative to Raven Lite, though it  
> has enough options to get my students into trouble! Thanks for  
> calling my attention to it.
> The power spectrum for Arethaea phalangium does techically show a  
> maximum peak at 15kHz, but there are several other peaks nearly as  
> high in the 10-15kHz range, and a few more biggies from 18-20kHz.  
> Not sure how to incorporate that into our identification guide! But  
> it does make me think that conventional katydid song descriptions  
> aren't yet optimal.
> Cheers,
> Alan
> --- In  "Avocet" <> wrote:
>>> Raven Lite's the only sound analysis software with which I'm
>>> familiar; this is probably unreasonable, but do you happen to know
>>> of any very inexpensive software that can generate power spectrum
>>> charts?
>> Alan,
>> Audacity - it's free. It does both audiograms and power spectra  
>> and is
>> worth putting up with a few fiddly wrinkles.
>> Sorry to be picky over the terminology but "peak frequency" can be
>> taken to mean the highest frequency or the frequency at the highest
>> level which is really the peak power frequency which can be anywhere
>> in the call.
>> If I have a variable pitch call I would select the peak frequency
>> (highest frequency) and plot the power at that frequency on the power
>> spectrum. If I want the peak power frequency (over the lenght of a
>> call) the power spectrum plotted over the whole call provides this.
>> David
>> David Brinicombe
>> North Devon, UK
>> Cogito cogito ergo cogito sum - Ambrose Bierce

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