Module 3-2: Digital Signals (Voice, Text, Image, Video) & Encoding

  • Due Oct 1, 2024 by 12:30pm
  • Points 10
  • Submitting a text entry box, a media recording, or a file upload

Module 3-2

 Digital Signals & Encoding

Voice signals start out as a pressure wave (which we can hear with our ears). Then they are converted to a voltage using a piezoelectric microphone. We can look at that voltage on an oscilloscope or computer screen, which we will do today (cool!). 

Digitizing a voice signal also allows us to do many things including filtering (taking out noise for instance), compressing the data (so we send less), easily recording and storing the signal, or even altering the signal (making your voice sound like a duck! or creating a false voice such as in a "deep fake"). We'll also talk about how smart phones and hearing aids work to help people hear better, and why hearing impairments are not the same the world over.

There are also many other kinds of digital signals smart phones send -- text, image, video, and other forms of data.  To effectively transmit any type of data, both the sender and receiver need to agree on a "language" or code that allows them to encode and decode the stream of 1 and 0's.  All of these signals have to be encoded for efficient transmission, allowing multiple signals to coexist in the air without interfering with each other, and security. Different countries have different standards governing privacy and security. Let's discuss the challenges of running a cellular network across international boundaries.

Learning Objectives

  • What's so big about the "digital revolution"? Why aren't we just doing everything in analog?

Pre-Class Assignment

NOTE: We will provide a number of online resources, some of which may be corporate sites that are advertising services or products. Using these sites as our references should IN NO WAY imply that we are promoting these companies. In some cases, we will even provide conflicting or debatable sites for the purpose of generating thought and discussion.

In Class Activities

ASCII short video.

ASCII Code Swap: Create an ASCII signal (short message), pass it to a friend / receive one from a friend, decode it.  We will use decimal codes for the letters, but real communications use binary.  Discuss preambles, acknowledgements, and closing to messages. Here's an ASCII table Links to an external site. (use the DEC decimal column).

level 2 ASCII: send the signal in a way that is more robust to "burst" noise.  In many cases, noise will block the signal for a short amount of time then go away.  We will create an agreement on how to reorder the signal in time and transmit one word that way as a class (whiteboard activity).  As humans we can infer when something went wrong by spell checking.  When too many errors occur, we can't figure it out though.  Information degrades with too many errors.

Error detection and correction: how can we figure out if the message we received was actually the correct one?  Parity checking Links to an external site. on words, or blocks of bits. Os use a checksum. Links to an external site.

ASCII encodes plain text.  But what about other forms of data?  MS Word documents, images, sound files, video, streaming video?  Think and discuss how we could do this (imagine the "language" that we would need for each type of data).

How to actually send a signal over airwaves?  Modulation.  How do we actually send 1's and 0's through radio signals for smartphones?  AM, FM, phase modulation, quadrature  (in class video).  

Packet transmission: Breaking long messages into chunks, sending chunks different paths to the same destination.  Containers and Headers.  Like containerization of shipping. 

What to turn in for "in class" today?  Copy your ASCII message (scanning the paper is fine) and submit it here. For homework, see below.

Extra Resources

Little more detail on ASCII:

 

JPEG encoding of Images:

 

Video Encoding:

 

Error Detection & Correction:

 

Packet Communicaitons / Internet / TCP/IP:  

Homework

Due by 9/28 at class time.  Pick one of the topics in extra resources above (or a different one).  Record a short audio or video response / summary (1-2 minutes only).  Click on the big red submit box on the top right of this page.  

 

1727807400 10/01/2024 12:30pm