Fundamentals of Audio Production, Chapter 11 1 1 Fundamentals of Audio Production Chapter Eleven: Transporting Sounds

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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• 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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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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• 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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• 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 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 cladding produces “total internal reflection”



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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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• 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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• 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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• 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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• “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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• Frequency modulation– The frequency of the carrier is altered by the

amplitude of the audio signal



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• 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

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Fundamentals of Audio Production, Chapter 11 1 1 Fundamentals of Audio Production Chapter Eleven: Transporting Sounds