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Fundamentals of Audio Production, Chapter 11
1Fundamentals of Audio Production, Chapter 11
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Fundamentals of Audio Fundamentals of Audio ProductionProduction
Chapter Eleven:Chapter Eleven:
Transporting SoundsTransporting Sounds
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Transporting Audio
• The method by which audio will be delivered to the consumer will determine how the content should be prepared.
• It is important to understand the limitations and capabilities of the various means of transporting audio.
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Copper wire technology
• Telephone circuits using a single pair of copper wires carried early radio signals
• AM radio bandwidths of 5 KHz
• Vacuum tube amplifiers or “repeaters” boosted the signals
• “Twisted pair” copper wire still provides much of the backbone for telephone transmission
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Copper wire technology
• Technological advances now permit twisted pairs to carry broadband audio
• Twisted pair also carries broadband data and video signals
• “Coaxial” cable introduced in the late 1930s allowed even greater bandwidth
• Coaxial cable became the standard for television signal distribution
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Copper wire technology
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Microwave technology
• Named for the extremely short wavelengths of Radio Frequencies used for transmission
• Microwaves travel only in straight lines
• Transmitted and received using tightly focused parabolic dishes
• Make use of relay stations
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Microwave technology
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Microwave technology
• Capable of travelling great distances – up to 40 miles
• Capable of extremely large bandwidths and high data rates
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Satellite technology
• Communication satellites orbit 22,300 miles above the equator
• Communication satellites orbit the earth once every 24 hours – They are synchronized with the earth’s orbit– Called “geosynchronous” orbit
• Satellites appear suspended above a point on earth– Appear “geostationary”
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Satellite technology
• Satellites vary according to power and RF band they utilize
• Low power lower frequency satellites are called “C-band”
• High power higher frequency satellites are called “Ku-band”
• “Transponders” receive signals from earth stations and re-transmit to earth’s surface
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Satellite technology
• Satellite radio services use the S-band and F-band segments of the spectrum to transmit multiplexed signals to subscribers
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Satellite and Microwave
A transmission system using microwave, satellite, copper and optical fiber
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Optical fiber technology
• Optical fiber is made from highly purified optical glass
• The glass is drawn into a single continuous strand with the diameter of a human hair
• Fiber optics use “total internal reflection” to reduce attentuation
• The glass stand is wrapped in “cladding” that reflects the light internally
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Optical fiber technology
Optical fiber cladding produces “total internal reflection”
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Optical fiber technology
EIAJ OPTICAL CONNECTOR
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Digital wired technology
• Integrated services digital network or ISDN developed in the 1980s, offers digital transmission over the telephone network
• ISDN terminals convert analog to digital, and vice-versa
• ISDN signals are exchanged between terminals – not over the Internet
• The bandwidth of ISDN allows CD quality digital signals to be transmitted in real time
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Internet based technology
• Audio files can be transferred over the Internet using the same telephone network previously described
• Files may transferred two ways– As complete files – like any other data file– As a stream – with data transferred
continuously in near-real time
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Internet based technology
• Coder-decoder (CODEC) software is used to compress audio files for Internet transfer
• Lower compression rates yield better bandwidth and dynamic range
• 1:1 compression is called “lossless” compression – preferred by audio professionals
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Internet based technology
• Two CODECs that support 1:1 compression are “AIFF” and “WAV”
• Higher compression ratios yield smaller files and faster transfers
• “Lossier” formats use compression ratios from 4:1 (MPEG1) to 53:1 (VOX)
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Internet based technology
• Streaming audio is sent continuously and played immediately as received
• Streaming software includes “buffers” which store data for a short time before playback
• Buffering avoids start and stop of the audio stream due to network traffic
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Internet based technology
• “Podcasting” – MP3 files distributed over the web– Uploaded to and downloaded from servers – Sent as emails– “Podcatchers” may use RSS aggregator
software to receive new content automatically – Still subject to copyright and music licensing
regulation
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Broadcast technology
• Audio may be transferred long distances using radio frequency broadcasting
• The radio frequency signal is modulated
• Modulation superimposes the analog signal on the radio frequency carrier
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• Amplitude modulation– The amplitude or strength of the carrier is
altered by the amplitude of the audio signal
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Broadcast technology
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Broadcast technology
• Frequency modulation– The frequency of the carrier is altered by the
amplitude of the audio signal
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Broadcast technology
• It is possible to transmit audio by radio in digital form
• Digital broadcasting has low distortion, excellent signal-to-noise ratio, and no signal degradation