2.6 Analog and Digital Signals

ANALOG vs. DIGITAL SIGNALS

Phenomenon

Vinyl records, like the one in the photograph, were used to record and play songs starting in the 1940s. Later CDs were introduced and were extremely popular until eventually telephones and cellular devices became all you needed to listen to music. The sound quality has changed as the way of storing the music has changed. When you put in a vinyl record you will often hear static as you play the music or the music may not even play correctly because the vinyl record is scratched or warped from heat. When you listen to a CD you don’t have issues with static but it can still be scratched and so you may have issues with it reading the CD correctly. Both of these issues are not a problem with an electronicdevice when listening to music. You can’t damage the files by scratching it and the static is not an issue as long as you have a good set of headphones. 

1. What are the differences between the three ways of storing music?
2. Why do you think storing digital recordings on (cd’s, mp3s) have mostly replaced vinyl records in recent years?
3. How do you think the structure of the waves in the three different devices is different from each other? 

SIGNALS

What if we want to measure or understand something...time, or light, or sound?  What if we want to record or send that information?  These days we have technology that can record an event on our phone immediatly, and share it on social media with our family who could be hundreds of miles away, and they see what we saw.  We can see the temperature outside or the time, without ever looking at a thermometer or a clock.  We are in the "digital" age......but what does that mean exactly?  Cameras don't use film.  Clocks are not round.  We can "download" any song we want to hear.  Before the digital age, technology was "analog".  Analog and Digital are different types of signals. The word analog means a continuous signal representing a quantity.  Any information can be conveyed by an analog signal.  It can show a physical variable like sound, light, temperature, position, or pressure.   Information is converted into an analog signal by a transducer.  An example is sound striking the diaphragm of a microphone, causing fluctuations in the electrical current produced by a coil of wire.  The energy current running through the wire is the ANALOG of the actual sound.  The energy flowing through the wire is a reproduction of the original sound.  A Digital Signal is a sampling of information, turned into a code of ones and zeros.  You are not hearing every sound wave in a digital recording, or seeing every light wave recorded in a digital picture. 

Analog Signals
In the past, before digital technology was invented, only analog signals were used to transmit information.
Analog signals are representations of actual images, sounds, words. They often use waves to transfer information. Analog signals do not use mathematical codes to transfer information. Examples of analog signals are conversations between people on an old hardline telephone.  Sound waves were converted to electrical waves which travel through a copper wire to another phone, then converted back to sound waves where your friend hears you speak. Film cameras use light waves to imprint the image on the film, which is a clear plastic base with light sensitive chemicals on it.  Vinyl records which use actual waves/grooves in carved vinyl to make the sound.  Vynal records are made with an aluminum core, sanded down smooth,  then coated with  nitrocellulose laquer, and a hole punched through the middle.  The laquer must be perfect, no scratches or imperfections. Next, in a sound studio, a record is placed on a lathe which is a cutting machine.  Sound is turned into an electrical signal that moves the lathe up and down, cutting grooves into the record that immitate ( are the analog) the sound.  This "master" copy is then used to mass produce carved vinyl copies. Some analog signals are simply an instrument used to make a measurement.  In sound waves,  frequency is the pitch of the sound, and wave height, or amplitude is the volume.  CD's are carvings into a plastic and metal disc, and are also analog signals. Tapes were analog, with sound waves recorded on a plastic film with a magnetic coating. An scratch, bend or imperfection causes the sound wave to be deformed and it will no longer sound like the original information. 

Almost any information can be converted into an analog signal to be sent by radio waves through the air, or electrical waves though wire. 

For example an alcohol thermometer is used for measuring temperatures and a grandfather clock measures time.
Can you think of some other examples of analog signals? 

An analog signal conveys all the information from the original source.  It conveys the full spectrum of light, and all frequencies and amplitudes of sound.  If you look at a round analog clock, you don't just know it is showing hours and minutes, but the hands pass seconds, and fractions of seconds.  Those fractions of seconds may not be painted on the clock face, but the hands of the clock pass through the whole spectrum of time measurements.  The motion of the clock hands is continuous and represent all the infinite values of time. Did you know there are many small measurements of time including:

Millisecond                        1/1000 of a second

Nanosecond                       1/billionth of a second

Picosecond                         1/trillionth of a second

Femtosecond                      1/quadrillionth of a second

Attosecond                           1/quintillionth of a second

Zeptosecond                        1/sextillionth of a second

Yocctosecond                       1/spetillionth of a second

The hands of our clock pass all of these. 

Digital Signals

Codes are something that has fascinated people for as long as humans could write. Sometimes students will create codes so that no one can read secret
notes but themselves or you will find codes in mystery books. While it may just seem fun, signals and codes have been used throughout history to prevent iinformation from falling into the wrong hands. For example, the code shown above is believed to have been used by George Washington to send secret messages during the American Revolutionary War.  Digital signals are information turned into a code of "ones" and "zeros".  A digital signal is created by "sampling" an energy wave.  That sample is given a numerical value, and that is then translated into a code language used by computers that consists of ones and zeros. Some information is lost in trasnlation.  Since just samples, and NOT the entire wave is being transmitted, you are not hearing or seeing all of the information that was in the original sound or light wave. There are gaps in the information.  However, the digital sampling happens so fast, and so many times per second, that your eyes and ears have a hard time seeing or hearing the difference between the original sound, and the digital copy.  If sampling happens at a fast enough rate, humans can't tell the difference.  IN the picture below an analog wave is "sampled" to be turned into a digital wave.  The sample values are then translated into a computer language we will discuss below.  

Everything that you see or hear on a computer—words, pictures, numbers, movies and sound--uses digital signals. Digital signals are sent as
mathematically coded waves. They can be sent over long distances. Once the waves arrive at a receiving station, they are decoded back into
information that you can understand. In the example of the computer, the signal will be sent to the screen which has it decoded back into an image that you will recognize or the code of digital sound files will be sent to your speakers where they will be decoded back into sound.
Electronic devices used today, including smartphones, handheld devices, digital thermometers, digital cameras and video game systems, work by transmitting and receiving digital signals in waves. A digital wave looks different.  It is square.  The digitized information can be easily stored in a computer and will never degrade or be damaged.  

What is the code it is turned into?  Its called a Binary Code, and its made up of ones and zeros.  You wonder how can all this information be stored and understood by us, with just these two symbols, one and zero.  A Bit is the smallest unit of data that a computer can process and store. A bit is always in one of two physical states, similar to an on/off light switch. The state is represented by a single binary value, usually a 0 or 1. A Byte is  a unit of data that is usually eight binary digits long. A byte is the unit most computers use to represent a character such as a letter, number or typographic symbol. A byte might represent character like the letter A,  which is 01000001, or the number 30, or a symbol on a map.  It is a whole language. Between each of the characters (numbers or letters) is a Nul Character or Delimiter,  that indicates the end of one character and the beginning of another.  How would we translate, for example, the number 30 into an 8 digit byte in computer language.  You go through a series of mathmetical steps that translate a number into its "remainder" when divided by 2.  Lets translate the number 30.

30/2= 15.  There is no remainder because two divides into 30 evenly..........translation  "0"

15/2= 7 remainder 1..........translation "1"

7/2=3 remiander 1............translation "1"

3/2=1  remainder 1...........translation "1"

1/2=0  remainder 1 (less than 1 =1) .......translation 1

Now reverse the remainders and you have translated : 1 1 1 1 0= 30

Can you think of other examples of digital signals?  

Here is an example of a digital wave:

Digital vs Analog

When analog technology is used to record a sound, every part of the sound wave is recorded. The recorded sound waves can be very complex,
because the recording device records every sound that it picks up, even background noises that are traveling through the air. The next picture shows an
analog wave.

When you are recording analog sounds it is easy for the recorded sounds to be slightly different than the actual soundwave. This is because when the sound is transmitted and recorded, it is hard for every part of the wave to be recorded exactly the same each time. Any additional background noise could be recorded with it, changing the wave and the sound. When sounds are recorded digitally, not every part of the sound wave is recorded. Instead, the recording device takes samples of the sound wave at certain periods and only records the information at that moment vs an analog wave that is recording at every moment. The diagram below shows the difference between an analog and a digital wave. The analog wave is smooth and rounded because it is constantly recording the information where the digital recording only records information periodically and doesn’t include the full wave. This would seem like it was a bad thing however because the digital wave is simpler it is easier to copy it or transmit it without there being mistakes in the copy. In digital copies the wave is not affected by any outside source and so the wave’s code stays the same and the sound file will remain unchanged.

If you were asked to remember a series of numbers would it be easier to remember 6 values accurately or 6000. Since digital is only a sampling of all of
the information it is only storing and transmitting a smaller number of values compared to analog which is storing and transmitting an infinite number of
values. Take the thermometer for example. The liquid in the alcohol thermometer moves up constantly with a temperature rise, showing every temperature change to the smallest degree that you may not even notice. Digital thermometers only increase at set values like 98.6 to 98.7. There are values for the temperature between 0.6-0.7, but the information is not stored or transmitted by the digital thermometer. 

https://www.youtube.com/watch?v=ZWdT-6Ld71Q