# Sound for Interaction class 5

## Interference and Beats

• Interference and Beats

Difference between two notes is called interval

## Frequency and Pitch

Frequency if the measure of how many cycles a wave complete per second.

Frequency (f) is measures in Hertz

Period (T) in the inverse of infrequency is is measured in seconds

Frequency = Cycles/Second Perdiod = Seconds/Cycle

f = 1/T T = 1/f

The perception is frequency is know as pitch.

### Intervals

An octave is doubling of the frequency.

ie 440 Hz is an A

the next A after 440 Hz is 880 Hz

In westen music the octave is divided into 12 semi-tones

## Phase

Phase in measured in degrees.

The phase of a sound has to do with the time domain.

Adding two Simple Harmonic waves -Applet

Adding two Simple Harmonic waves2 - Applet

## Timbre/Harmonic structure

Timbre is a descriptive word used to help describe the 'color' and envelope of a sound.

All sound is made up of simultaneous sounding tones. In the 1700 Joseph Fourier a French mathematical physicist proved that all sound can be synthesized be adding sine waves. The way these sine waves are added together make things sound different.

Different sound don't sound the same due to different fundamental frequencies, harmonics, complexity, and envelope.

Timbre is made up of Harmonics and Envelope. The Harmonics define the different frequencies present in a a sound and the envelope defines the amplitude through time.

### Harmonic Structure

http://www.rane.com/par-t.htm Harmonics defined @ rane

Understanding Harmonics Fundamental Frequency and Harmonics Instruments

```   * Guitar string
* Open-End Air Columns
* Closed-End Air Columns
```

Natural harmonics are multiple of the fundamental/

Understanding Harmonics @ Harmony Central