S522, Kewley-Port
Spring, 2008

Assignment #13

Assignment on Spectrograms and LPC, Week 13, due 4/16

SPECTROGRAMS

A) Get spectgr.m from DSPFIRST. Download specdkp.m and alligator.wav from Oncourse->Resources->spec.

B) Use wavread to read in 'alligator.wav' with FS = 8000 Hz. Make a wide band and narrow band spectrogram of alligator.wav using specdkp.m. Print the wideband spectrograms to turn in.

C) Investigate what happens to the display when the 'nlap' (or 'noverlap') parameter is changed. This is the number of samples common to the overlapping time windows, and should be in the range of 50-80% of the number of samples in the window. Vary 'nlap' at some extreme values (2% vs. 100%) to see what the effect is, both on calculation time and the display. Print an example that is very different than in (B), and briefly explain the effects of changing the overlap..


 LPC

Download Colea from http://www.utdallas.edu/~loizou/speech/colea.htm, upzip and make ready to use.

The overall purpose of this assignment is for you to replicate the steps in Markel & Gray to produce most of their Figure 1 (for a vowel) and Figure 2 (for /s/). The speech sample is in Oncourse->Resources->spec. The file is 'tellsam.wav'. Put it in your Colea directory. Try things out in Colea. If you have problems with some displays etc. , exit Colea, and type "Clear all" or "Clear func", and then reenter.

1) Select a vowel for processing to simulate Markel & Gray processing in Fig. 1, and and /s/ for Fig. 2. Show on a plot the waveform sections that you analyze.

2) Process your vowel with Colea or MatLab and turn in your version of plots for Fig. 1A, 1C, 1D, 1E and 1F. Using Colea you may wish to calculate 1D first, and then subtract to get inverse spectrum, 1C. To view either the FFT or LPC spectrum in the MatLab workspace:

  1. Edit PLLPC.M
  2. Set Break point at line #182.
  3. In command window, you will see "K>>" for "keyboard mode". This allow you to examine the variables in the Colea workspace.The variable "dBMag" has either the LPC or FFT magnitude spectrum (in dB) in it.
  4. Save this Colea workspace to a .mat file: save ae1.mat
  5. Exit keyboard mode with "return" command. Release breakpoint with F12 in edit window.
  6. Load ae1.mat, and you have all the variables from Colea to manipulate (especially dBMag).

On 1D, explain why you selected window n and order m. On 1E and/or 1F, explain how your error signals differ from the ideal ones in Fig. 1.

5) Process /s/ and turn in your version of plots of Fig. 2A, 2C, 2D, 2E and 2F (you may order them like Fig. 1 if you'd like). Comment on your LPC order and your error signal.

{Updated on 4/5/08}