Speech Science - Transmission of Speech

Transmission of Speech

Speech is transmitted through sound waves, which follow the basic principles of acoustics. The source of all sound is vibration. For sound to exist, a source (something put into vibration) and a medium (something to transmit the vibrations) are necessary.

Since sound waves are produced by a vibrating body, the vibrating object moves in one direction and compresses the air directly in front of it. As the vibrating object moves in the opposite direction, the pressure on the air is lessened so that an expansion, or rarefaction, of air molecules occurs. One compression and one rarefaction make up one longitudinal wave. The vibrating air molecules move back and forth parallel to the direction of motion of the wave, receiving energy from adjacent molecules nearer the source and passing the energy to adjacent molecules farther from the source. Sound waves have two general characteristics: A disturbance is in some identifiable medium in which energy is transmitted from place to place, but the medium does not travel between two places.

Important basic characteristics of waves are wavelength, amplitude, period, and frequency. Wavelength is the length of the repeating wave shape. Amplitude is the maximum displacement of the particles of the medium, which is determined by the energy of the wave. A period (measured in seconds) is the time for one wave to pass a given point. Frequency of the wave is the number of waves passing a given point in a unit of time. Frequency is measured in hertz (Hz; cycles per second) and is the perceived as pitch. Each complete vibration of a sound wave is called a cycle. Two other physical properties of sound are intensity and duration. Intensity is measured in decibels (dB) and is perceived as loudness.

There are two types of tones: pure tones and complex tones. The musical note produced by a tuning fork is called a pure tone because it consists of one tone sounding at just one frequency. Instruments get their specific sounds — their timbre — because their sound comes from many different tones all sounding together at different frequencies. A single note played on a piano, for example, actually consists of several tones all sounding together at slightly different frequencies.