DTC 354 Digital Storytelling Rebecca Goodrich

Wave made up of changes in air pressure by an object vibrating in a medium—water or air.

As the object moves, it compresses air molecules, causing an areas of high pressure alternating with low pressure.

Alternating high and low pressure causes the eardrum to move back and forth, which stimulates structures in the inner ear, which send nerve impulses to the brain.

A similar mechanism is at work in a microphone. Air pressure causes a membrane to move and generate electrical signals, which are sampled and encoded digitally.

Frequency = number of full cycles per unit of time. Usually measured in Hertz = number of cycles per second.

Pitch = how high or low we perceive a sound to be. A high frequency = a high pitch, and vice versa.

The human ear generally perceives sounds between 20Hz and 20,000 Hz.

Which is the higher pitch? 20 Hz 200 Hz

Most sounds are a blend of many frequencies and, thus, many different pitches.

Sound To review….

Sampling: collecting data at regular points in the sound cycle.

Sampling rate = how often we collect the samples. Sampling rate is also measure in Hz (confusing  ). Stands for samples per second. CD quality = 44,100 Hz.

Intensity = objective measure of sound energy measured in decibels. Indicated by the amplitude of the waveform. Loudness is subjective. 100 decibels may be uncomfortable for me but fine for you.

Bit depth = measure of frequency range that is sampled. Human ears function mainly between 2000Hz and 5000Hz, so that’s a standard bit depth.

High sampling rate + high bit depth = high fidelity Sounds great! However……

High sampling rate + high bit depth = high fidelity Sounds great! However…… Large files, longer file transfer rate

Reduce sampling rate Nyquist’s theorem = you must sample at least 2 times in each sound cycle for a sound to be recognizable. Reduce bit depth Reduce the number of channels from 2 to 1 (stereo to mono) Apply compression