Assignment 2, Weeks of Feb. 15 and 22: Report Due: Tues. March 2

Using Filters

• Reading: chapters 4 and 5 of the text.
  
  
• In the lab:
  
  
  • Do Problem 4.7. This asks you to design a simple feedforward filter that blocks zero frequency (DC bias) and an input phasor at frequency one-sixth the Nyquist. Implement in ein, seeing how well such a sinusoid is actually blocked. (Use the lower sampling frequency so things are easier to hear.) Is the output exactly zero? Mix the sinusoid at frequency (f_N)/6 with another at frequency (f_N)/12. How well does the filter remove one and pass the other? What is the theoretical prediction?
    
    
  • Do Problem 5.7. Don't worry if you don't get through part (c). This asks you to give the transfer function and input-output equation for a variation of reson with zeros at +-sqrt(R). This reson can be swept in frequency by varying the center frequency and the gain will remain very close to constant. Try this in ein. Sweep a reson over a wide range of frequencies while filtering (1) white noise (random numbers), and (2) your favorite sound files. Experiment to see what the effects are of sweeping very fast, and of sweeping back and forth over different ranges.
    
    
  • When you get right down to it, comb filters don't sound all that great. They are buzzy, flat and mechanical. The buzzy part can be ameliorated by low-passing the signal, however, and the flat and mechanical aspects can be fixed by doing some wobbling on the delay line length (L1, etc). Also, multiple combs with slightly different frequencies can give you a nice result. Do one or more "studies" which explore these suggestions.
    
    
  • Learn how to use rt. The help/overview menu item will bring up a help page.
  
  
  
• What to submit:
  
  
  • On paper, your theoretical work on Problems 4.7 and 5.7.
    
    
  • In the directory /var/cs325/_your_user_name_, einscripts and soundfiles for the parts above.

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