DTC 354 Digital Storytelling

Rebecca Goodrich

Sound

What is sound?

What is sound?

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.

A waveform is the visual representation of the sound wave.

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….

Digitizing Sound

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

How can you reduce the size of a file?

Reduce sampling rateNyquist’s theorem = you must sample at least

2 times in each sound cycle for a sound to be recognizable.

Reduce bit depthReduce the number of channels from 2 to 1

(stereo to mono)Apply compression

How can you reduce the size of a file?