Nature of Sound Vibrations

Sound vibrations occur in two modes:

1. Natural vibrations in the air, resulting from mechanical compression/rarefaction waves;

2. Oscillation of electronic voltage (synthesizers)

3 classifications of sound vibrations can be made, based on the above criteria:

1. pitched/periodic

2. noise/non-periodic

3. clangorous sound

The following diagram illustrates the three types:

I. Pitched/Periodic

• vibrations are repeated at a regular equidistant constant rate

• mind interprets resulting vibrations as a constant pitch

There are 2 types of pitched sound:

__a. simple__

• sine tone; 1 frequency (ƒ1)

• simplest vibration; only produceable by electronic oscillator; used as an audio test pattern

__b. complex__

• musical instruments, voice, etc.

• electronic oscillator waveforms ie triangle, sawtooth, rectangular waves

**Jean Fourier** (1768-1850) scientist who hypothesized that complex tones are made from several combined sine waves; different waveforms are the result of different collections of sine waves

**Fourier Analysis**- analysis of sounds into parts

**Fundamental tracking**-ability of the mind & ear to interpret harmonic frequencies as reinforcing the bottom-most frequency, known as the fundamental (ƒ1)

• collection of sine waves known as overtones/harmonics/partials

Overtone Series

• overtones are multiples of starting frequency (fundamental)

• predictable mathematical ratio of fundamental to overtones are expressed as integer relationships (A 110 is ƒ1: ƒ2-220, ƒ3 is 330, ƒ4 is 440, ƒ5 is 550, ƒ6 is 660, etc)

• expressed in musical terms as a grand staff w/ overtones

• staff is a logarhythmic system

• the number of partials and their relative strengths determind a sound’s timbre/waveform,

& frequency content

II. Random noise; non-pitched sound

• random noise is the result of all frequencies vibrating at random

__A. Acoustic medium__

• wind, surf, waterfall, jet engine, etc

__B. Electronic medium__-Noise Generators

1. white sound: humans hear higher frequencies better because our minds hear it that way

2. pink sound: weighted toward lower frequencies

3. blue sound????-theoretical, but perhaps possible!

III. Clangorous sound

• clangorous sound includes inharmonic frequencies which weaken pitch center, mask fundamental

**Inharmonic frequencies**-overtones which are not within overtone spectrum;

the result is that overtones and fundamental are masked, distorting mind’s ability to perceive pitched sounds through fundamental tracking;

the higher the number and amplitude of inharmonic frequencies, the more "clangorous" the resulting sound will be

__A. Acoustic medium__

• percussion instruments: metal, membranophones ie bells, cymbals, vibes

__B. Electronic medium__

• sounds which contain frequencies not in harmonic series, known as sidebands, resulting from complex FM algorithms