Fourier Transform Based Analysis
This technique relied on the Fourier Transform to determine the
frequency sections of the audio signals. This process shared all the parameters of
the filter based analysis except the filter order.
The first step of the process was to break the signal into time intervals.
The Fourier Transform was then applied to each interval. The resulting frequency data was then
broken into a number of section, and low pass filtered to produce an amplitude envelope. This
envelope data was averaged and the various frequency section were used to construct a vector
of frequency range values. When this process was applied to each interval in the signal,
it produced a vector set describing the time and frequency characteristics of the input
This process required that all audio signals have the same sampling
frequency for the resulting vector sets to be comparable. While birds have been known
to vocalize up to 15000 Hz, the vast majority stay within the range of 4000 - 9000 Hz.
As such, it was decided to accept a sampling frequency of 22050 Hz to maximize the data
set. Since some of the audio recordings obtained were sampled at 44100 Hz, these recordings
were converted to 22050 Hz before being processed.