1. Sound is caused by changes in air pressure that create sound waves. These waves have properties like amplitude, frequency, wavelength, and phase. 2. Frequency refers to the number of pressure change cycles per second and is measured in Hertz. Higher frequencies are heard as higher pitches while lower frequencies have lower pitches. 3. Harmonics are integer multiples of the fundamental frequency which determine the tone quality or timbre of different instruments and voices.

1. Fundamentals of Sound Lecture
What is Sound?
Sound is both a physical
phenomenon, and our
perception of it.

2. Orders of Sound
• There are three (or technically four)
orders of sound/audio that we are
concerned with:
1. Acoustics or Objective Sound (and
Psycho-Acoustics or Subjective Sound)
2. Analog Audio
3. Digital Audio

3. Sound is Pressure
The sounds which we hear are based on sound waves.
These are longitudinal waves of molecules which result
from regularly repeating changes in air pressure. A sound
wave consists of micro-variations in air pressure above or
below the ambient air pressure.

4. Sound Is Pressure

5. Amplitude
The distance between the positive and negative peaks is known
as the amplitude.

6. Frequency
The speed at which one of these cycles is repeated every second is
known as the sound wave’s frequency and is expressed in Hz. If the
air is vibrating very quickly then the frequency will be a high number
such as 15,000 Hz. If the air is vibrating slowly then it will be a low
number such as 40Hz.

7. Decades of Audio

8. Wavelength
The wave length is the distance through the air
that a sound wave travels to complete one of its
repeating cycles.

9. Calculation of Frequency vs Wavelength
The frequency f specifies the number of cycles per second, measured in
hertz (Hz). Frequency and wavelength are related as follows:
• Wavelength (ft) = Speed of sound (ft/sec)/ Frequency (Hz)
which can also be written as:
• Frequency = Speed of sound/ Wavelength
The speed of sound in air is about 1,130 ft/sec at normal conditions.
For sound traveling in air our equation becomes:
Wavelength = 1130 / frequency (Hz)

10. Phase
Where might you find this short phase delay?

11. Harmonics
The second harmonic (or first overtone), twice the frequency of the fundamental, sounds
an octave higher; 2:1 (octave)
The third harmonic, three times the frequency of the fundamental, sounds a perfect fifth
above the second. 3:2 (perfect fifth)
The fourth harmonic vibrates at four times the frequency of the fundamental and sounds
a perfect fourth above the third (2 octaves above the fundamental). 4:3 (perfect fourth)
Double the harmonic number means double the frequency
(which sounds an octave higher).

12. Harmonics

14. Audio Definitions
• Sound waves are changes in pressure.
• Amplitude is the amount that the pressure changes.
• Frequency is the speed that the pressure changes.
• Phase is difference in pressure change between the left
and right ear.
• It is important that you understand these concepts since the
purchase of equipment, the manipulation of sound and the
recording of sound all depend on how the equipment
responds to each aspect of a sound wave. We will be
dealing with these three concepts for the rest of the
semester.

15. Audio Basics ADSR
Attack--how the sound starts. A sudden rise in amplitude is a fast attack. A slow
increase in amplitude would be a slow attack. Sounds that make you jump usually have
a very quick attack.
Decay--After the initial rise in amplitude the perception of the sound usually decreases
slightly.
Sustain--How long does the sound stay at a steady amplitude (volume). The different
lengths of sustain are the main differences between a sneeze and a shout. A sneeze has
a very short sustain.
Release--How does the sound die away? A sound that stops short or sounds "cut-off"
would have a quick release. A sound that slowly fades away would be a slow release.

16. Transducers
mic-level signal (~2 millivolts) to Line level (~1.23 volts in pro gear)
A mic level is very weak. An XLR cable is a specific format of cable designed
to carry mic level signals. In other words, XLR cables carry mic level signals
and we need to use mic preamps to amplify a mic level signal into a line level
signal.