How are you hearing Me?

Basic Diagram of Cell Phone Communication: annotate this diagram as you read.

Part 1: Speaking into the phone ~ Turning Speech into Digital Information

When you speak, the motion in your vocal cords is transferred to motion energy in the air.  Your vocal cords move quickly back and forth. When your vocal cords move forward, they push the air in your throat, creating a high-pressure front of air. This is quickly followed by your vocal cords moving backwards and creating a space with much less air (or low-pressure front). These tiny, rapid changes of high-low-high-low-high-low pressure fronts traveling out of your mouth toward the phone are called sound waves. The microphone and processor in your cell phone convert the information in a sound wave into digital information. This digital information is really as simple as a long string of 1’s and 0’s representing highs and lows of these waves coming from your vocal cords.   For example, 110110101001010001101001101001.

Part 2: How your cell phone sends the digital information to another cell phone

The converted sound wave is now an electric signal inside the cell phone.  Your phone encodes (or translates) this information into radio waves.  Even though radio waves are invisible to our eyes, they are a type of light wave.  Radio waves  oscillate between high-low-high-low like sound waves, but also have many important differences. One of the most notable differences is that sound needs air or another medium to travel through, but light, being made up of electric and magnetic fields can travel through empty space. (Note also, since light is made up of oscillating electric and magnetic fields it is often referred to as an electromagnetic wave.)

Another important difference is that while sound travels superfast, over 300 m/s in air, light travels super duper fast, near 300,000,000 m/s in air.  That’s 67,000,000 miles per hour!

Once your voice is encoded and broadcasted by your cell phone’s antenna as radio waves, it can quickly travel to the nearest cell tower.  From the tower closest to you, your signal gets re-broadcasted to the tower closest to your friend’s phone.  Finally, your signal is  re-rebroadcasted by the second tower to your friend’s phone.  This whole process takes place in less than 1 second.

Part 3: From Your Friend’s Phone to their Ear

Once this digital signal (encoded in the radio waves) reaches your friend’s cell phone antenna, the digital signal then is converted back into an electrical signal. This electric signal is then processed by their phone.  The phone sends a signal to the speaker where it is  converted back into a sound wave similar to your voice. This process of hearing someone’s voice from far away is why telephones are called telephones -- that is, tele = “far away”, phone = “sound”, so telephone = hearing someone’s sound (voice) from far away.

When your friend hears these sound waves, it is their ears responding to the tiny, rapid changes in the pressure of the air. Speech is a complex mixture of waves with different frequencies and amplitudes. Each frequency oscillates a different part of their inner ear. The bigger the amplitude of that frequency, the bigger the oscillation of that part of their ear. The bigger oscillation of that part of your inner ear, the bigger nerve signal that part of your ear sends to your brain. The typical high school student’s ear can perceive sound ranging in frequency from 20 to 20,000 Hz.

Part 4: Trade-offs of digital information and transmission

Cell phones, with their ability to send digital signals and store that digital information, have changed how society interacts. Transferring and storing information digitally has many advantages over older technologies such as vinyl records, cassette tapes, and paper. Information (like a song on Spotify or a video on YouTube) can be easily stored, copied, and shared while taking up little to no physical space. Since digital data only consists of 1’s or 0’s, the information is resistant to corruption or degradation. While a vinyl record could get scratched or a cassette could get wiped, the same information stored digitally is easily preserved.

Although the power of digital data storage holds a lot of advantages, there are also disadvantages to consider. Because digital data is so easily copied, leaks of information can occur. Every few months in the news there are stories of individuals, companies, or governments getting information stolen in massive quantities. Using the same technology that stores information, criminals sometimes take advantage of the technology for their own purposes.

Using the reading above and prior experience outline an argument about the advantages and disadvantages  of digital information and transmission.

Advantages:

A.

B.

C.

Disadvantages:

A.

B.

C.

Part 5: Coding in ASCII

By encoding different types of data into specific binary number schemes, digital storage allows us to archive a wide variety of information that is often difficult to encode. Any kind of numerical data can be represented using binary notation on digital media, and any kind of information that can be encoded in numerical form (which almost any kind can!) is storable too. Text, for example, is represented quite easily with the binary ASCII code, eight bits (each with a 0 or a 1) for each character, including punctuation marks, and spaces. Here is an example of the ASCII code:

When a computer is processing ASCII, it breaks the digital information (string of 1’s and 0’s) into chunks of eight 1’s or 0’s. Each chunk is called a byte and encodes a number, letter, or punctuation mark. The first few numbers distinguish whether the code represents a number (001) or a letter (011). For example:

011001000110111101100111        →         01100100     01101111    01100111        

       raw digital information        →             byte                   byte              byte

                                                     d                o                g                →                      dog

See if you can decode these messages:

A) 0110011101110010 00111000                                          _____ _____ _____                        (3 byte file)

B) 0110100001101001001000000011010100100001        _____ _____ _____ _____ _____        (5 byte file)

C) Encode your own message.