Course: CSCB09: Software Tools and Systems Programming Summer 2019

Professor: Albert Lai

Assignment: 3

An implementation of a biquad filter that suppresses high frequencies while preserving low frequencies using Unix pipes to chain program instances together.

Plotted with gnuplot showing the frequencies of the "ugly.wav" file pre-filtering (ugly.txt), and the resulting suppression of high frequencies as "out.wav" (out.txt).

• towav.c
  • converts WAV files to readable input for the program
• unwav.c
  • converts output of program to a WAV file
• ugly.wav
  • starting frequency to work with
• All shell commands and pipelines

• biquad.c

  • an implementation of the difference equation given by :

    

• cascade.c
  • utilizes biquad.c to create multiple pipelines of biquad.c for use in filtering
• run.sh
  • a file created from provided commands for ease of compiling

To run the files, I have created a small shell script to ease the compiling process.

-b runs the biquad pipeline

-c runs the cascade file

-g graphs the plot above (requires gnuplot installation)

E.g.

$ ./run.sh -b

Notes about the file compilation and compiling separately with different arguments is provided below, this script is only for working with the ugly.wav file we are provided here.

Requires a C compiler and *nix Environment before you can play around with arguments

Listen to ugly.wav

Compilation with GCC compiler:

$ gcc biquad.c -o biquad
$ gcc cascade.c -o cascade
$ gcc towav.c -o towav
$ gcc unwav.c -o unwav

Piping biquad instances:

$ ./unwav < ugly.wav | ./biquad 1 0 1 -0.7 0 | ./biquad 1 1.18 1 -1.58 0.81 | ./biquad 4.42e-3 1 0 0 0 | ./towav > out.wav

Then listen to out.wav and see if you can spot the frequency difference!

Alternatively, we can use cascade.c to implement the pipeline instead which will create the same result:

$ ./unwav < ugly.wav | ./cascade 1 0 1 -0.7 0 1 1.18 1 -1.58 0.81 4.42e-3 1 0 0 0 | ./towav > out.wav

The plot in the first section was generated by:

$ ./unwav < ugly.wav | head -300 > ugly.txt
$ ./unwav < out.wav | head -300 > out.txt
$ 
$ gnuplot
$ plot 'ugly.txt' with lines, 'out.txt' with lines