 Chapter 3 Audio and Video Technology Basic principles Basic Principle of Media Technology Facsimile Technology - All modes of mass communication based on this process of copying Fidelity - a way to describe how faithfully a facsimile represents the original High Fidelity is reproduction that closely approximates the original signal Radio waves can be used to transmit facsimiles of pictures and sounds Transduction Transduction - the process of changing one form of energy into another form For example:  Capturing sound of a bird chirping using a microphone involves the transduction of sound waves into electricity In the case of image, light into electronic current Transmitting the sound and image of the chirping bird involves transducing the electrical energy into electromagnetic energy Digital—The Good, the Bad, and the Ugly Digital signals are subject to less noise interference than analog signals Compression—making larger video and audio files smaller Pro: Digital files can be more easily manipulated Con: Digital files can be more easily copied and distributed illegally Two basic concepts that are involved in the process of transduction Oscillation and wave form Oscillation Oscillation - a basic concept of audio and video signal processing Examples –  Vibration of air produced by speech and other sources make sound; vibration of light frequencies make up all theimages we see Electromagnetic waves used for transmission of radio, TV, satellite are also oscillate The rate of oscillation of a radio, sound, or light wave defines its frequency Wave form Waves may be described in terms of frequency and amplitude Frequency is the number of waves that pass a given point in a given time Frequency is usually measured in hertz (Hz) The higher the frequency the shorter the wavelength Amplitude is the height or depth of the wave from its normal position  Frequency Response How well a radio reproduces a range of audio frequencies is an example of describing its frequency response How faithfully television represents the original image is thought of in terms of picture resolution  CDs can reproduce the entire range of audio frequencies that the human ear can hear (20 to 20,000 Hz) AM stations cannot reproduce all the frequencies the human ear is capable of hearing; FM radio comes much closer, etc. The FCC determines a station’s bandwidth when it determines what frequencies that stations can use; bandwidth impacts info capacity and thus sound and picture quality Signal generation, recording, transmission Signal Generation and Recording Mechanical and Digital Technologies For example, sound signals are generated by two main transduction processes:  Mechanical: microphones (phonograph records and tape recorders) Electronic: CDs, DVDs, and computer files Digital Recording Technology Sound and images that has been transduced into electrical current are sent to a device that converts them into a series of samples Once in digital form they are coded and stored ELECTROMAGNETIC SPECTRUM • Upper end of the spectrum includes visible light which ranges from red to violet. • Above violet = ultra violet • Below red = infrared. Radio Bands in the Electromagnetic Spectrum Low – Navigation signals Very Low (VL) – Time signals, long-range military comm. Medium Frequency (MF) – 107 AM channels, air and marine radio High Frequency (HF) – International Shortwave, CB, and Ham radio  Very High Frequency (VHF) – FM radio and TV channels 2 - 13 Ultra High Frequency (UHF) – UHF (Most DTV channels), police radio, radar and weather satellites Super High Frequency (SHF) – Ku and C band satellites, Microwave transmission, air navigation Extremely High Frequency (EHF) –special military communications Spectrum Management Spectrum management - the process of defining and keeping track of what frequencies will be assigned and licensed for special purposes Allocated for specific purposes by the ITU (International Telecommunications Union) Allotted to countries. Assigned by each country’s licensing organization (e.g., FCC). The process known as transduction is used at several points to accomplish modulation of the carrier frequency. Radio AM Broadcast Service Assignment Method -- Frequency Search Band -- MF (Medium Frequency) 535-1705 kHz Channel Width -- 10 kHz (1075-1085 = 1080 kHz) AM Continued Operate on 60 clear, 41 regional, or 6 local channels Min/Max Power -- 250/50 kw  Stations are designated as class: A (highest power; 10 to 50kw) B (5 to 25 kw) C (regional, 500 to 5000w; local 250 to 1,000w). FM Broadcast Service Assignment Method -- FCC Assignment Table (Part 73, FCC Rules & Regs) Band -- VHF (Very High Frequency 88 -108 mHz Channel Width -- 200 kHz (97.1 mHz = 97.0 - 97.2) SCS (Subsidiary Communications Service) Mulitplexing (Stereo) HD FM Radio Classified as  A (up to 3kw; HAAT max 300 ft.) B (up to 50kw; HAAT max 500 ft.) C (100kw, max. HAAT 2,000 ft.) Low Power FM (up to 100w; HAAT max 100)  Min/Max Power -- 100 w/100 kw HD Radio – Does it stand for anything? FCC approved iBiquity’s HD radio technology in 2003 HD radio technology was developed and is owned by iBiquity Digital Corporation In-band, on-channel (IBOC) - IBOC signals use the same AM or FM bandwidth as the station’s analog signal (in-band); digital information is contained within the station’s signal (on-channel) Advantages of HD radio over analog radio Higher quality sound Multicasting Auxiliary information (artist, name of song, weather, news, traffic) Improved reception??? Current analog signals will remain HD Radio is FREE! HD radio receiver is needed to pick up digital portion of signal Industry projects that radio will go all-digital once technology matures Currently 1,500 radio station broadcasting in HD IBOC uses COFDM (Coded Orthogonal Frequency Division Multiplexing) to multiplex a digital stream on to the FM or AM carrier. Satellite Radio Digital audio radio service (DARS) - satellite delivered direct-to-home or car DARS is a form of DAB In 1992, FCC allocated space in S-band (2.3 GHz) of frequency spectrum for nationwide broadcasting of DARS In 1997, FCC