Audio and Video Communication

Transmission of Audio Without wires - This is radio. Using wires - this is what we typically think of as basic telephone technology. Cell Phones – Microwaves (E&M waves) and Fiberoptic cables Internet – Satellites, phone lines, Fiberoptics (both wireless and wired)

Cell Phone Frequency Range: 850 and 1900 MHz

Cell phones and Microwave Ovens are close together on the Frequency Spectrum… Microwave Ovens use 2.45 GHz (GHz = 109 cycles per second) GSM Cell Phones use 850MHz and 1.9GHz Why don’t cell phones “cook” you?

How a Microwave Works Microwaves are absorbed by water, fats, and sugars (the stuff in food) Water is a dipole molecule with a positive and negative side Water molecules constantly flip over, trying to align themselves with the changing electric field of the microwave As the water molecules flip over they rub against each other making heat http://www.sciencelearn.org.nz

Transformer steps up the voltage to 2000 volts Magnetron produces the microwave Waveguide leads wave into oven cavity

Difference between Cell Phone and Microwave Oven Power Cell Phone 0.1 Watts Microwave 1000 Watts Amplitude Modulation Cell phone is carrying info Microwave is not

More Information can be transmitted if information is Digitized

Voice and Music are analog data Dots-Dashes, 1’s and 0’s, on-off are examples of digital data Digital information is coding a signal using a binary format, e.g. 0’s and 1’s, dots and dashes, on and off, Morse Codes, etc. Analog is the process of converting a signal into a wide range of continuous values.

Photographic picture is an analog image. www.bbc.co.uk Digital picture is made up of many pixels, each pixel is one color. http://photo.net/equipment/digital/basics

Record Vinyl is analog data Record Vinyl is analog data. The grooves are carved by a needle that was moved by a vibrating needle attached to a diaphragm. The groves are analog as they are a continuous representation of the audio information. http://www.nps.gov birminghamstories.co.uk

Record Needle - Stylus Placed in the grooves of the recorded disc and transfers its vibrations to a magnet that induces a current in a nearby coil, creating an electrical signal that corresponds to the audio. As the stylus rides along the walls of the moving groove, it vibrates back and forth with each ripple in a wall. Two transducers attached to this stylus sense its motions and produce electric currents that are related to those motions. Transducer: Converts input energy of one form into output energy of another form. Louis A. Bloomfield http://www.answers.com

Electromagnets used in Tape Players too The electromagnet consists of an iron core wrapped with wire, as shown in the figure. During recording, the audio signal is sent through the coil of wire to create a magnetic field in the core. This flux is what magnetizes the oxide on the tape. During playback, the motion of the tape pulls a varying magnetic field across the gap. This creates a varying magnetic field in the core and induces signal in the coil that corresponds to the audio. A – Tape HowStuffWorks Tapes can store analog data (a continuous signal) or can be DAT (Digital Audio Tapes)

Transmission of Audio This is Amplitude Modulation (AM) Amplitude is volume and frequency is the pitch. Audible range: 20 Hz - 20 kHz Turned into a Electromagnetic Wave http://www.answers.com

This is Frequency Modulation (FM). This requires greater bandwidth but it is easier to cancel out noise. Turned into a Electromagnetic Wave

Transmission of Analog Data (Listening to the Radio or talking on the phone ) was preferred over Morse Codes (dots and dashes) because: Transmitting dots and dashes (digital data) required a human computer to decode the message. Transmission speed was slow

Voice data can be automatically sent digitally by digitizing the audio and then reassembling the audio later. Periodically take a sample, at a rate of at least ½ the frequency. The more samples the more information is captured. /www.webbasedprogramming.com

Digitized Sounds http://jvsc.jst.go.jp

CD Rom- Digital data storage Data is represented as pits and bumps Track is a outward moving spiral http://invsee.asu.edu/nmodules

CD Bumps are the digital data Data Track is typically 3 ½ miles long.

Reading the bumps with a laser and optical sensor

Click for animation http://electronics.howstuffworks.com/cd5.htm

The tracking drive keeps the laser under the track. The disk motor spins between 500-300 rpm as the laser moves outward with the track. Animation at: http://electronics.howstuffworks.com/cd6.htm

How data is arranged on CDs Data is interleaved so scratches on the CD won’t be a complete loss of data Data is read one revolution at a time, and software orders the interleaved data in the correct sequence. Extra data is present for error-checking Meta-Data is present to identify songs

Video Communication Producing Video Images Capturing Video data Transmission via cable Transmission wireless Storing Video data on VHS Tape Displays CRT LCD Plasma Digital TV and DVDs

Brain assembles pixels into images Higher resolution means more dots/pixels for a given area Higher Res. Means sharper image Brain fuses pixels How Stuff Works

Brain assembles still images into a life-like moving image 19th century novelty items Old movies – 16-24 frames/sec Theaters – 24 frames/sec TV – 30 frames/sec http://www.isntlifeterrible.com

Praxinoscope http://brightbytes.com/collection/

TV ‘paints’ image with three electron beams Hot Cathode emits electrons.

Shadow Mask holes are arranged so that each electron beam corresponds to one color and can only excite one phosphor dot http://www.nickelinstitute.org

Steering coils around CRT position the electron beams using magnetic fields CRT - Cathode Ray Tube

Electron Beams ‘paint’ the screen using a raster scan pattern 525 Lines are ‘painted’ every 1/30 second. Each line has 680 pixels.

Lines are interleaved Every other line is painted to reduce flicker Odd lines are ‘painted’ in 1/60 of a sec. followed by even lines painted next.

Inside of the screen is coated with stripes made of three phosphors: They each glow red, green, or blue. Shadow Mask ensures that each beam strikes only the phosphor it was intended for. http://www.meko.co.uk/shadowmask.shtml

Colors are fused by the Brain RGB can be mixed to create any color of varying intensity.

TV broadcast uses Radio Signals Each station allocated 6 MHz 54 to 88 MHz for VHF channels 2 to 6 174 to 216 MHz for channels 7 through 13 470 to 890 MHz for UHF channels 14 through 83

TV uses AM for video and FM for audio www.sfu.ca/sonic-studio

Luminance (intensity), Chromaticity (color), and sound

Luminance for one line

Chrominance Signal Phase shift after sine wave determines color for one pixel.

Recording onto tape Video Head Drum is tilted with respect to the tape. This creates diagonal video tracks. The drum rotates quickly, making long video tracks. There are two record/read heads attached to the rotating drum. One screen picture is two diagonal tracks, or one rotation of the drum. Yellow tracks are audio and control tracks

Magnetic Data on Tape Control Track indicates if this is a SP, LP, or EP and thus determines how fast to pull the tape. It also ensures the heads are lined up correctly during playback. Audio track is recorded and read similar to tape deck. http://videoexpert.home.att.net/artic2/211vcrw.htm

TV goes Digital in Feb. 2009 19.39-megabit-per-second (Mbps) stream of digital data Multiple formats can be transmitted Standard Definition High Definition (HDTV)

Digital Modulation Techniques Phase Shift Keying (Bluetooth, Wireless LANs) Frequency Shift Keying (GSM Phones) Amplitude Shift Keying (Sending Morse Codes using Telegraph, optical fibers send pulses of light representing 1’s and 0’s) Some Combination of the above

Monitors Cathode Ray Tube (CRT) Flat Panel (Liquid Crystal Display) In most TVs Bulky, heavy, higher power Good color and display Image needs to be refreshed Warm-up time requirement Flat Panel (Liquid Crystal Display) More expensive Images may vary based on viewing angle Low Power

Polarized vs. non-Polarized Light http://www.geo.umn.edu Light with the Electric Field in one orientation is polarized light.

Liquid Crystal Displays Glass plates are electrodes Applying a voltage across the plates aligns the liquid crystals parallel to the voltage Small one-directional scratches on the glass plates cause the crystals to twist when there is no voltage http://en.wikipedia.org/wiki/Liquid_crystal_display

Polarizing Filters A thin film on a surface absorbs light with the horizontal orientation. Only light with a non-horizontal orientation passes through. http://science.howstuffworks.com/sunglass2.htm

Liquid Crystal Displays LCDs block light creating darkness Vertical Polarizing Filter 7-segment display with metal oxide that is both transparent & conductive. Backside has verticals ridges. Liquid crystals Layer with horizontal ridges Horizontal Polarizing Filter Reflective layer to reflect light back to your eye wikipedia

LCD with applied voltage – light is blocked or absorbed by filters creating darkness. LCD without voltage – light is passed through or reflected

Color is achieved with three sub-pixels: Red, Green, Blue Voltage for each color determines intensity of the sub-pixel. Color filters filter out all light but the one color for the sub-pixel.

Sources http://www.howstuffworks.com/tv.htm http://www.physics.utoledo.edu/~lsa/_color/31_tv.htm