Download Distinguishing Characteristics Frequency Sound and Electrical Waves

Sound and Electrical Waves
• Definition
•
Periodic variation in air pressure
• As we speak, vibrations created by our vocal cords travel
in the medium of air
• These vibrations travel through the air and cause sound
wave just like a boat moving through water causes waves in
the water
Wave in either air or water
emanating from a source
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Inc.
Sound and Electrical Waves
• Distinguishing Characteristics
•
Frequency
• Definition:
• Number of occurrences during a specific period of time
• Examples: Frequency of the seasons, full moons, etc.
• As used in Communications
• Used to distinguish between the different sounds wave of that
sound will occur in one second
• The period of a wave is the length of time required for one
wave
Five cps analog waveform
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Inc.
Sound and Electrical Waves
• Distinguishing Characteristics
•
Frequency
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Inc.
Sound and Electrical Waves
• Distinguishing Characteristics
•
Wavelength
• In sound the standard unit of time is a second
• Definition
• The physical length of one waveform
Pictures Copyright (c) 2007 by Pearson Education,
Inc.
Sound and Electrical Waves
• Distinguishing Characteristics
•
Amplitude
•
Term used to describe the strength of a signal
Voltage is used to measure
the signal strength of
various amplitudes. The
greater the amplitude, the
louder the sound and the
stronger the signal.
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Inc.
Sound and Electrical Waves
• Frequencies Peoples use in Communications
•
•
The full range of frequencies that can be heard is 20 –
20kHz
Most of the information in human speech can be
represented with 300 – 4000 Hz
• Telephones use this smaller range as a historical compromise
that balances the information content with reliable
transmission distance
• Compromised developed during the late 1800’s and early
1900’s
• Sound Waves verses Electrical Waves
•
Within the frequency limitations of the telephone
• The sound waves and resulting electrical wave track
• They have different speeds
Sound and Electrical Waves
• Sound Waves verses Electrical Waves
•
Within the frequency limitations of the telephone
• The sound waves and resulting electrical wave track
• Different wavelengths due to the different speed
» 250 Hz sound wave travels through the air at 331.5 m/s and
has a wavelength of 1.326 meters
» A 250 Hz analog electrical signal leaveing a telephone on a
pair of wires has a wavelength of 3x108m/ 250 = 1.2 x 106m
• However both still have the same frequency and period
» 250 cycles per second or 250Hz
» And each cycle takes 0.004 seconds to complete