Sine Waves

Acoustics: Physical properties of sound

Acoustic signal is the medium for speech communication

Sounds are described as waves

Source: Stone thrown to a river, tuning fork, falling book hitting the ground

Medium: Air or water particles

Sound Wave Propogation

• Movement of a sound source

• Movement of air particles

• Fluctuations in air pressure

Fluctuations in air pressure include…

• Compression=together (high pressure)

• Rarefaction=few (low pressure)

Wave propagates, air particles do NOT!

Waveform

• Waveform shows air pressure variation across time

• A sound source that vibrates at a certain frequency results in a sine wave

Cycle- Part of the waveform that repeats itself at regular time intervals

Period (T)- The duration of a cycle

Frequency (f)- The number of times that a periodic event repeats itself for a standard time interval (left to right) (number of cycles per second) (measured in Hz)

Amplitude- Maximum deviation from the zero line in air pressure (up and down)

• An acoustic measure of air pressure

• Can be converted to dB based on fixed air pressure to reflect the wide range of loudness

• Primary acoustic correlates of loudness perception

Phase- Timing of wave propogation

• Two waves can have the same amplitude and frequency, but be out of phase

• Most important to sound localization

Propagation velocity (c ) - Speed of sound, defined as distance traveled in a standard amount of time (35,000 cm/sec)

Wavelength- Distance between recurring events