Sound waves

A sound wave is a pressure wave that is perceptible to the human ear. Sound waves can be produced by the human voice tract, machines, animals and other sources, and disseminate in a variety of mediums: solid, liquid or gaseous. Sound waves are subject to the usual physical effects of reflection, diffraction, breaking and absorption. The speed at which sound waves disseminate depends upon the transmission medium: 330 metres per second in the air, several thousand metres per second in some solid materials. The audible frequency range for the human ear is between 20 and 20,000 Hz. Sound outside this range is referred to as ultrasound or infrasound. Sound waves cannot disseminate in a vacuum, as they always require a transmission medium. In this respect, sound waves differ from electromagnetic waves, for example.

Conversion of sound into electrical signals and vice versa

Loudspeakers or microphones are used to produce sound waves via electrical devices such as music systems or telephones or to convert sound waves into electrical signals. In the case of microphones, sound brings about voltage changes, thus allowing sound waves to be converted into electromagnetic waves. Loudspeakers generally operate on electrodynamic principles and convert electromagnetic waves into sound waves with the help of membranes and coils.

Transmission of sound waves in telephony

In telephony, the frequency range of the transmitted sound waves is limited to between 300 and 3,400 Hz. (with the exception of HD telephony). The sound waves are converted into electrical signals by a microphone and transmitted in analog or digital form via the telephone network. For digital transmission, the analog signal has to be transformed into a digital signal by means of sampling, quantisation and coding. Digital signals can also be transmitted via mere data networks. Voice-over IP (VoIP), for example, uses the Internet for transmitting digital voice data. This makes it possible to access the services of a cloud telephone system via any Internet connection.