1. 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 Sound and Electrical Waves Wave in either air or water emanating from a source Pictures Copyright (c) 2007 by Pearson Education, Inc.

2. 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 Sound and Electrical Waves Pictures Copyright (c) 2007 by Pearson Education, Inc. Five cps analog waveform

3. Distinguishing Characteristics Frequency Sound and Electrical Waves Pictures Copyright (c) 2007 by Pearson Education, Inc.

4. Distinguishing Characteristics Wavelength In sound the standard unit of time is a second Definition The physical length of one waveform Sound and Electrical Waves Pictures Copyright (c) 2007 by Pearson Education, Inc.

5. Distinguishing Characteristics Amplitude Term used to describe the strength of a signal Sound and Electrical Waves Pictures Copyright (c) 2007 by Pearson Education, Inc. Voltage is used to measure the signal strength of various amplitudes. The greater the amplitude, the louder the sound and the stronger the signal.

6. 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

7. 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 3x10 8 m/ 250 = 1.2 x 10 6 m However both still have the same frequency and period »250 cycles per second or 250Hz »And each cycle takes 0.004 seconds to complete Sound and Electrical Waves