EE235 Lab 1 – Introduction to Python and Signals Solved

EE 235 Lab 1 – Introduction to Python and Signals

In this lab, you will work through a series of exercises to introduce you to Python with an emphasis on the basics that you need to know for working with signals. You will learn to use variables, perform basic operations, and write your own scripts to run in Jupyter Notebook.

Lab 1 Turn-in Checklist

• Pre-lab: Show that you have installed or can access the necessary software by creating a Jupyter notebook that demonstrates basic Python functions and uploading it to canvas.
• 5 Assignment check-offs with TA
• Lab 1 Jupyter notebook with code for each assignment in individual cells and with

  markdown cells used for the lab overview and response to report questions.
  Note: All assignments except the prelab should be completed in groups of 3-4 people.

  Pre-lab

  Read Sections 1-3 of the Background document. Set up your laptop in order to be able to use Python and Jupyter notebook. Section 2 describes one option, which is to use Anaconda. You can also use ECE or CoE remote desktop services. See the ECE computing page for more information.

  Create a Jupyter notebook (prelab1.ipynb) that demonstrates the use of print, playing audio, and creating documentation using a markdown cell to your TA, as outlined in section 3 of the Background document. You will need to download the audio file provided on the Lab 1 assignment web page and save it in the same directory as your Lab 1 notebook. Save the prelab1 notebook and submit the file to the lab 1 assignment on Canvas.

  Download the template notebook for lab 1 (TemplateL1.ipynb) and rename it Lab1-XYZ, where XYZ are the initials of the lab partners. Your Lab 1 notebook should be organized according to this template.

  Lab Assignments

  This lab has 5 assignments. Each should be given a separate code cell in your Notebook, and each should be followed by a markdown cell with discussion. Your notebook should start with a markdown title and overview cell, which should be followed by an import cell that has the import statements for all assignments.

  Assignment 1: Creating and Manipulating Arrays

  Read Section 4 of the Background document. This assignment will have four parts, A-D, each of which should be indicated with comments, following the guidelines in the Lab 1 template. In creating arrays, you should use numpy, so don’t forget to import it.

Report discussion: Comment on the difference between concatenation and addition of two

vectors. What are the constraints in terms of when these functions can be applied?

template, A.

B. C. D.

Note: You

Show that

start a new cell and write a script to meet the following specifications.
Create digital versions x and y of the functions below over 0 ≤ t ≤ 3, with a sampling

frequency fs = 2.
x(t) = 0.5t y(t) = t2

Assign z to be the digital version of z(t) = x(t) – 2y(t) In w1, store the value of z(t) at t = 2. Print w1.
Store the values of z for 0 ≤ t ≤ 1.5 in w2. Print w2.

may need to cast your indices to integers. Use index = int(index)

your output matches the below:

EE 235 Lab 1 B. Extract the value 6 from y1 to store in ca. In cb, store the last two elements of y1. In

A. Create an array y1 with values 4, 6, 2.
d, store the number of elements in y1. Print ca, cb and d.

C. Create two arrays of length 5. The first (x1) should have all elements take the value 2, and the second (x2) should range from [-2,2]. Use the ones and arange attributes of numpy. Print x1 and x2.

D. Create arrp = x1+x2, and arrc as the concatenation of x1 and x2. Print arrp and arrc.

Run the code in this cell and verify that the results are what you expect.

Assignment Check-Off #1 of 5: Demonstrate this Assignment to the lab TA

Assignment 2: Amplitude Operations on Signals

Read Section 5.0-5.2 of the Background document. Again, following the guidelines in the Lab 1

Assignment Check-Off #2 of 5: Demonstrate this Assignment to the lab TA

Report discussion: Discuss how the results of this problem would change if you used fs=1

instead of fs=2.

EE 235 Lab 1 Read Section 5.3 of the Background document. Start a new cell following the guidelines in the

Lab 1 template, dividing it into Parts A-D.

1. Read in the files “train32.wav” and “tuba11.wav” using either the scipy wavfile package or simpleaudio, saving the audio vectors and sampling frequencies in variables y1, y2, fs1, fs2, respectively. Print the number of channels to confirm that the train file has 1 channel and the tuba file has 2.
2. Play the two sounds in their correct form and then with the sampling frequencies swapped.
3. Determine the length of the two signal and extract a section of the longer one that is the same length as the shorter one, called y3. Add two equal-length, single-channel signals to create y4. Play and write out y4 using sampling frequency fs1.
4. Concatenate the signals in y1 and y2, adding a 4 second pause between them. Call the new signal y5. Play the new signal and write it out to a file using sampling frequency fs1.

Assignment 3: Working with Sound Files

Assignment Check-Off #3 of 5: Demonstrate this Assignment to the lab TA by playing the

signals y4 and y5

Assignment 4: Plotting Comparisons

Read Section 6 of the Background document. Start a new cell following the guidelines in the Lab 1 template, dividing it into Parts A and B.

1. Define a time vector signal over -2 ≤ t ≤ 4, let fs = 5. Then create digital versions of the following signals for this time span:
   w(t) = |t|
   x(t) = 2 – t

   y(t) = -0.5t2

2. Plot all three signals in one figure with a grid and a legend. Be sure to label the time axis and title the figure.

Assignment Check-Off #4 of 5: Show the plots to the lab TA

Report discussion: Read the plot documentation and explain how you would change the

command to distinguish the signals using different line styles (solid, dashed, dotted) to make the

figure easier to read for someone who is color blind.

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Assignment 5: Plotting Sound Files in Subplots

Start a new cell following the guidelines in the Lab 1 template, dividing it into Parts A and B.

1. Create time sample vectors for the audio signals from Assignment 3 (y1 and y2) using the original sampling frequency for each, and name them t1 and t2. (You will need to use the signal lengths you found in that assignment.)
2. Plot the two signals side by side using a 1×2 subplot. Adjust the x and y axis limits to have the same ranges in both plots. Be sure to title the plots and label axes appropriately. For the time axis, you should plot time in msec, for which you will need to multiple the time array by 1000 as in the example in the Background document. Do not use grids on the subplots. Adjust the spacing to avoid overlap.

Assignment Check-Off #5 of 5: Show the plots to the lab TA

Team Report

When you’ve tested and cleaned up all your code (remember, you should only submit code for the Assignments, each in their own cell), go to ‘File’ then ‘Download as’, then select ‘.ipynb’. The file you download is a Notebook that your TA will be able to open and grade for you, once you submit it on Canvas. Remember, only one notebook per team! Make sure that your notebook is titled Lab1-XYZ.ipynb, where XYZ are the initials of the lab partners. You may want to also download the file as pdf to have a nicer documentation of your records.

EE 235 Lab 1

Report discussion: Comment on the differences between the plots of the signals. Can you see

the difference in sampling rate in these plots?

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