Audio Engineering Test 1

Sound Wave

energy transmitted through a medium from one location to another by particle interaction, thus it can be called a mechanical wave

How is frequency perceived?

As pitch(def: how often a sound wave repeats in one second)

timbre

harmonics and relative intensities

Amplitude

Energy of a sound wave

How is amplitude measured?

Decibels

Parts of a sound wave

Compressions(crests), rarefaction(decreased air pressure)

Frequency range of Human hearing

20 kHz to 20k kHz

Phase

refers to the time relationship between two or more sound waves at a given point in their life cycle together.

Constructive intereference

Sound waves are in-phase when they coincide

Destructive intereference

out-of-phase when they don’t coincide

What happens when something is 180 degrees out of phase?

It becomes desructive

ASDR

Attack, sustain, decay, release

Waveform

the graphic representation of a sound’s energy overtime

Waveform Envelope

characteristic variations in level that occur over the duration of a played note (over time)

Harmonics

whole number multiples of the fundamental

Octave

Doubling of frequency

Outer Ear

Sound is collected in the aural canal by way of pinna(outer ear) and directs sound to the ear drum

Middle Ear

Ear drum(stretched membrane) changes sounds into mechanical vibrations, hammer, anvil, and stirrup connects to the eardrum, and they amplify and limit transients

Inner Ear

Vibrations applied to the cochlea, which is fluid-filled and lined with tiny hair receptors (cilia) which respond to certain frequencies and stimulate auditory nerve

Fundamental frequency

The name of the lowest frequency in complex tone

Transducer

responds to pressure variations produced by sound & generates impulses

Ossicles

The three bones(hammer, anvil, and stirrup) that connect to the eardrum and help amplify/limit transients with mechanical vibrations

Cochlea

Fluid filled and lined with cilias, which respond to frequencies and stimulate auditory nerve

SPL

Sound Pressure Level

PTS

Permanent Threshold Shift

TTS

Temporary Threshold Shift, recovers after several hours, Mechanism used by auditory system to protect themselves

Signs of PTS

Muffling of speech, turning up music to hear, yelling when talking

Sensitivity relating to hearing

140 dB SPL (Threshold of pain), 120 dB SPL (Threshold of feeling), 0dB (Threshold of hearing)

Equal loudness principle

Equal loudness chart pictured (for every three dB raised, cut listening time in half)

Masking

when loud signals prevent ear from hearing softer sounds(i.e. louder sound ‘hides’ the softer sound), greatest when frequencies are similar, also used in modern delivery mediums

Temporal Fusion

Listeners hear direct sound and reflections, Brain ‘fuses’ into one auditory image, < 30ms are ‘fused’, > 30ms perceived as separate echoes

How to protect hearing

!. Take 15 min breaks, wear earplugs, Spl’s >75, check hearing with doctor

Acoustics

The study of sound/describes the behavior of sound waves in the room

Psychoacoustics

Analyzing how hearing works

Hearing aid vs. Cochlear implant

Implant requires a surgery, while the aid does now

Field of Audio crossovers

How to read Equal Loudness chart

Acoustical treatments applied to a room

Improve room “acoustics” (control unwanted room reflections) using ...•strategically placed absorbers, diffusers, and bass traps

Absorption

some sound energy“absorbed” by surface material

Reflection

Sound reflects off of surfaces at angle equal (and opposite) to angle of incidence

Diffraction

spreads around barriers bends through an opening

Diffusion

scattering of sound in all directions on reflection from a surface

How to calculate wavelength

1130/frequency

Life cycle of sound

Direct Sound, early reflections, Reverbrations

RT60

Amount of time for reverb to die away by 60 dB

Vertical Direction

Used with pinna effect

Our ears can use what

Arrival time difference

NIOSH

no louder than 85 dB

Why can’t sound go to infinity

Loses energy due to friction

Waveform parts

Compressions and rarefractions

Sound Pressure levels

dB-SPL

Vaccum

What sound can’t travel through

Pinnae

External ear

Direct sound tells us

Tamber and Direction

Htz

cycles/second

Ear is most sensitive to

2-5 kHz

Short sine vs Long sine

more wave cycles/shorter vs less or longer wave cycles

How to create acoustical isolation

Asymmetrical room, Isolation booths, strategically placed absorbers, diffusers, and base traps