Sound:
Sound is a longitudinal wave through particles in an environment (Longitudinal meaning the direction of the waves’ oscillation is the same as the direction of travel). Sound waves are produced when the vibration of an object sets the particles of a medium in motion. Sound waves cause air to compress and expand, resulting in areas of high and low pressure. The movement of particles determines the frequency and amplitude of a sound. Frequency is determined by the rate of movement of particles. Amplitude is determined by the displacement of the particles, the larger the displacement, the more pressure can be found in the bunching of particles, resulting in a louder sound.
Frequency:
Frequency is the number of waves (also referred to as cycles) that pass a fixed point in a given amount of time, for example cycles per second. Frequency is measured in hertz. Hertz can be described as the number of waves that pass a fixed point per second, so one hertz is one cycle per second. Frequency can be displayed on a spectrogram. The y-axis is the value of the frequency, the x-axis is time. Volume is displayed though colour, in this spectrogram the dynamics of the frequencies are displayed with yellow, meaning loud, the quieter frequencies shown in red and blue, then to black meaning silence. Spectrograms can be used as a tool to understand timbre (the quality of a sound). Different sources of sounds have different timbres as a result of overtones. Most things vibrate at more than one frequency, overtones are the frequencies that are found above the fundamental pitch. Changes in overtones can be caused by the dynamics of a sound. If a sound has very few overtones it’s described as dark whereas if it has lots of overtones it’s described as bright. An octave is double the frequency of the fundamental pitch.
Anatomy of the ear:
Sound waves are directed into the ear canal by the outer ear, the sound waves then travel through the ear canal to the eardrum. The fluctuations of pressure in the air cause the ear drum to move back and forth. This then causes three tiny bones in the middle ear to move, setting the fluid in the inner ear in motion. Hair cells can be found in the inner ear, the movement in the fluid causes them to bend, they then convert this movement into electrical impulses which are then received by the brain. Hair cells further into the inner ear receive higher frequencies, as higher frequencies travel further in fluid.