June 6, 2004
Problem Set
13: LabView and FFT with MatLab
(LabView lab writeup)
This problem set is a program of analysis of
waveforms which will be captured in class, during the lecture time. For a guide on how to set up LabView, capture
waveforms, transfer them to your unix file system, and analyze them with
MatLab, see the lab writeup entitled “Digital Waveform Capture with LabView” (http://www.physics.sfsu.edu/~bland/courses/490/labs/minilabs/labview/labview.html).
In class, a signal will be provided for you
to analyze. It will be a note sung at a
pitch somewhere near middle C. The exact
pitch will be determined by someone else, with the frequency given to the
instructor but not to you. Someone will
also be recorded singing the first two bars of
“Papa Haydn’s Dead and Gone.”
1. Make a plot of the waveform, and of its
Fourier power spectrum, using MatLab.
Identify the dominant frequencies in the spectrum.
2. Determine the fundamental frequency, and thus
the note of the scale being sung. For
finding the note, use the well-tempered scale, where the scale starting with
middle C has the frequencies
where
n = 0,1,2,3, . . . 12 refer to C, C#, D, D#, E, F,F#,G, G#, A,A#,B, and C.
3. Explain the other frequencies occurring in
the power spectrum as well as you can (in terms of harmonics of the fundamental
frequency of the musical note, electromagnetic pickup, etc.)
4. Make a spectrogram of someone singing “Papa
Haydn’s Dead and Gone,” and identify significant features of the spectrum.