Properties of Sound

Making Waves

Sound Waves

■Sound is created by vibrations

Sound Waves

■Sound is created by vibrations

■Vibrations move air molecules near them

Sound Waves

■Sound is created by vibrations

■Vibrations move air molecules near them

■Molecules forced together, raise air pressure

Sound Waves

■Sound is created by vibrations

■Vibrations move air molecules near them

■Molecules forced together, raise air pressure

■Pressure is transferred to other molecules

Sound Waves

■Sound is created by vibrations

■Vibrations move air molecules near them

■Molecules forced together, raise air pressure

■Pressure is transferred to other molecules

■This causes a ‘Wave of Pressure’.

■Zero line is pressure of air at rest

0 line

High

Low

■Zero line is pressure of air at rest

■High points represent higher pressure

0 line

High

Low

■Zero line is pressure of air at rest

■High points represent higher pressure

■Low points represent lower pressure

0 line

High

Low

■Amplitude - change in pressure from a wave’s highest point, to it’s lowest point

AmplitudeCycle

■Amplitude - change in pressure from a wave’s highest point, to it’s lowest point

■Cycle - refers to the time it takes for the wave to go from one amplitude, through all its changes...to the same amplitude again.

AmplitudeCycle

■Frequency - the number of cycles per second

■Frequency - the number of cycles per second

■One Hertz - equals ONE cycle per second

■1000 Hz = 1000 Cycles per second.

■Sound is converted to electrical energy and sent through wires

■For transmission, sound is converted to electrical energy and sent through wires

■For transmission, sound is converted to electrical energy and sent through wires

■Analog - recorded on cassette tape as changes in magnetic strength

■For transmission, sound is converted to electrical energy and sent through wires

■Analog - recorded on cassette tape as changes in magnetic strength

■Digital – recorded and stored on a hard drive as a ‘file’.

■Analog Recordings - sample the wave forms at peaks and valleys

■Analog Recordings - sample the wave forms at peaks and valleys

■Digital Audio - samples the sound and turns it in to 1's and 0's

■Analog Recordings - sample the wave forms at peaks and valleys

■Digital Audio - samples the sound and turns it in to 1's and 0's

■The higher the sample rate the greater the number of sampling points per second

■Analog Recordings - sample the wave forms at peaks and valleys

■Digital Audio - samples the sound and turns it in to 1's and 0's

■The higher the sample rate the greater the number of sampling points per second.

■Lower sampling rates do not capture the true sound being recorded

■Lower sampling rates do not capture the true sound being recorded

■Sampling rate must be at least TWICE the frequency

■Lower sampling rates do not capture the true sound being recorded

■Sampling rate must be at least TWICE the frequency

■Therefore if frequency is 8000Hz... the sampling rate must be at least 16,000 times per second

■Lower sampling rates do not capture the true sound being recorded

■Sampling rate must be at least TWICE the frequency

■Therefore if frequency is 8000Hz... the sampling rate must be at least 16,000 times per second

■A CD recording is sampled 44,000 times per second.

2 Identical Sound Clips (Grey)Sampled at 2 different rates (Blue)

Audio Task

■Open the Voice Recording Assignment sheet in the Handout Folder. Read and practice the printed short story

■Using one of the USB Microphones in the classroom, record the short story in your computer and then Export it as an MP3 file to your Broadcasting Folder.