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This module describes how a matched filter algorithm is used to identify birdcall audio files.

Matched filter implementation

Matched filter

Matched filters do an excellent job of identifying sound samples, so we decided to apply the method here to identify birdcall audiofiles. A matched filter searches for a sample clip, the filter, within a longer audio recording. Convolution compares the filter to the longer signal at eachpossible offset. The greater the maximum amplitude of the convolution result, the stronger the match. By having a different filter for each birdcall, we cansearch an audio file to identify which birdcall it contains.

The matched filter algorithm is as follows:

  • Reverse the filters in the time-domain.
  • Normalize the energy of each of the filters.
  • Convolve each filter with the input signal and take the maximum amplitude of the resulting convolution signals.
  • The filter that gives us the greatest maximum value indicates which birdcall the signal contains.

Filter library creation

Our first step in implementing the matched filter algorithm was to create a library of birdcall filters. To do this, we looked atthe spectrograms of a few sample audio files of the same birdcall and selected a portion that looked representative of the call.

For each birdcall, one of the representative audio segments was saved as a filter. Because the first two steps of the above matchedfilter algorithm affect only the filter library and are independent of the input signal, we reversed the filters and normalized their energy before saving themto wave files.

Matlab implementation

The following MATLAB script performed our matched filter algorithm. When given a wave file as input, it would tell us how well theaudio sample matched against each of the 6 birdcall filters.

We used circular convolution instead of linear convolution because it computed much faster. MATLAB's built-in cconv functionzero-pads the two signals before multiplying their FFTs, generating the convolution result we are looking for.
function result = birdcheck(file) [sig, fs, nbits]= wavread(file); signal=sig(:,1);signal=signal/max(abs(signal)); filters{1}=wavread('filters/bob.wav');filters{2}=wavread('filters/lt.wav'); filters{3}=wavread('filters/lw.wav');filters{4}=wavread('filters/pygmy.wav'); filters{5}=wavread('filters/red.wav');filters{6}=wavread('filters/redcry.wav'); for i=1:6filter=filters{i}; result(i) = max(abs(cconv(signal,filter(end:-1:1))));end end

The script was able to correctly identify several birdcalls. It did fail to correctly identify four cases in twocategories:

  • Two of our loon tremolo files registered as pygmy owl common songs.
  • Two of our red-tailed hawk shriek files registered as red-tailed hawk cries.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
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What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
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Damian Reply
absolutely yes
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Akash Reply
it is a goid question and i want to know the answer as well
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Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
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Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
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Source:  OpenStax, Birdcall identification project. OpenStax CNX. Dec 17, 2008 Download for free at http://cnx.org/content/col10616/1.2
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