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List any two factors in which time and frequency depend?
Sound is the mechanical disturbance of a medium, either gas, liquid or solid. For example, when a piano key is struck, the movement of the string disturbs the surrounding medium, air, causing the displacement of molecules. This disturbance has a knock on effect causing adjacent molecules to be disturbed over a certain distance until the initial energy created by the initial displacement has disappeared. The energy decays to zero after being transferred from one molecule to the next, in the process losing an amount through each transferral.

In a more practical context sound can be described as the transmission of pressure, from an initial sound source to a listener through the air.

Sound has three stages which affect how it is perceived by a listener.

    The initial character is shaped by the properties of the sound source (i.e. an instruments' material and shape) and its excitation, such as being hit, plucked or breathed into.
    The environment and the mediums which sound travels through to the listener. For example, a shout heard in a canyon sounds different than if heard in a small room, or through a pair of speakers. See section Elementary Acoustics)
    The listening conditions applied by the listener. The individuals subjective perception of sound as well as their physical condition (i.e. the shape of the outer ears, or someone's age), affects how sound is perceived by the listener (this is discussed in the section, Sound and the Ear).
Sound pressure is transmitted in air as a wave like motion. In air, sound waves have a pressure which alternately deviates from a state of equilibrium. These deviations are regions of compression and rarefaction of molecules.


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