Audio Midterm

Properties of Sound Wave

wavelength
amplitude
frequency
period
velocity

Wavelength

\
relationship btwn frequency and wavelength

the distance between successive crests of a wave in meters or ft

peak \= max compression

trough \= max rarefaction

frequency and wavelength \= inverse relationship (i.e. lower frequency, longer wave)

Amplitude

\
standard measure of units

visualization of amplitude phenomenon

magnitude of the molecular displacement, sound pressure level

dB \= standard measure of units

newton's cradle \= visualization of the amplitude phenomenon
\-- magnitude of molecular displacement near a sound source will proportionately displace the molecules at a distance \= changes in loudness

Frequency

\
standard measure of unit

relationship between waves in period and pitch

The frequency refers to the number of sound waves a sound produces per second.

fewer waves in period \= lower pitch

f\= 1/time period

Hz \= standard unit of measure is the number of cycles per second

Period

time it takes to complete one cycle

where wave intersects x axis

Velocity

used to describe the speed at which sound waves travel

Mach 1.0 speed \= 770 mph

Envelopes of Sound

\
what are the sections?

rise and fall in volume of one note

four sections of envelopes: attack, decays, sustain, release

Attack

note rises from silence to max lvl

Decays

max to midrange lvl

Sustain

middle level

Release

note falls from its sustain level back to silence

Damp

add resistance to vibrating object so that its vibrations die out more quickly after a note is sounded

sine wave

pure tone of a single frequency

complex wave

sine waves of three frequencies combined: fundamental, overtones, harmonics

fundamental frequency

determines the pitch of the sound

overtones

higher frequencies in the complex wave

result from frequencies whose interplay produces tones at the sum/difference of those component frequencies (44o Hz + 220 Hz \= 660)

gives sound its timbre

harmonics

overtones that are integral multiples of the fundamental frequency

determines the tone quality/timbre

Psychoacoustics: how ear interprets sounds

- locations of sounds are detected
- how pitch is heard/perceived
- how the ear separates complex auditory signals occurring simultaneously

attenuation

amplitude declines as the listener moves from the sound source

Audible Frequencies

20 Hz - 20,000 Hz

ear most responsive to 1,000 Hz - 6,000 Hz

shape and folds of the ear alter reception of frequency sounds

Principle of Equal Loudness (Fletcher Munson)

for all frequencies to be perceived as equally loud, the amplitude of frequencies outside the mid ranges (1,000 Hz - 6,000 Hz) must be increased

AKA. equalization

Frequency Masking

a sound at one frequency tends to mask softer sounds at nearby frequencies

i.e. 1000 Hz tendency to mask 500 Hz tone

ear's limited ability to simultaneously process sounds of multiple pitches

Inter-aural Time Difference

the short delay it takes for a sound to reach the ear furthest from the sound source

Interaural Level Difference

relative amplitudes of the sounds
shadowing effect of the head lowers the amplitude of the more distant sound → comb filtering

Hearing

when a person speaks, air molecules around the ear are compressed.

The compression wave of air molecules moves away from the speaker by being pushed into the next layer of air molecules
when molecules bounce back after being pushed, the air molecules produces a sharp reduction in their compression \= rarefaction

Phase Cancellation

180 degree phase shift between two identical waves, the peak of one wave coincides with the trough of another. when two waves combine, they cancel each other out \= no sound

Hearing Loss

120 dB \= threshold of pain --\> amplitude at which irreparable or permanent damage begins to occur

ear ringing \= indication that sound pressure levels were at/near the threshold of pain

dependent on genetic predisposition and environmental hazards

typically occurs in 40s-60s

Hearing Loss

how many min and at what dB can person listen to music?

90 min/day \= 90 dB

20 min/day \= 100 dB

Temporal Masking

phenomenon in which the human ear has difficulty hearing a soft sound that follows a loud sound closely in time

Feedback

phenomenon that occurs when a microphone picks up sound from a speaker while that speaker is playing sound from the microphone, thus creating a loop.

Microphone Designs

Moving-Coil Dynamic
Ribbon
Condenser

Dynamic Moving Coil Microphone

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How it Works

Application

Pickup Patterns

a coil wire attached to a diaphragm suspended in a magnetic field
sound waves vibrate diaphragm → coil vibrates in magnetic field → generates electrical signal

application: guitar amps, drums

pickup patterns: uni and omni

Dynamic Ribbon Microphone

\
How it Works

Application

Pickup Patterns

thin metal foil suspended in magnetic field → sound waves vibrate ribbon in field → generates electrical signal

application: horns and guitar amps

pickup pattern: bi and hypercardioid

Condenser Microphone

\
How it Works

Application

Pickup Patterns

metal backplate and conductive diaphragm placed very close together → charged together → form two plates of a capacitor
sound waves strike diaphragm → vibrates → varies spacing between plates → varies capacitance → generates signal using electrostatic field

application: acoustic instruments, cymbals, studio vocals

pickup patterns: uni, omni, and bidirectional

Pick-Up Patterns

omnidirectional

unidirectional
- cardioid
- supercardioid
- hypercardioid

bidirectional

subcardioid

omnidirectional mic

equally sensitive to sounds from all directions

unidirectional mic

most sensitive to sound arriving from front but softens sounds entering the sides or rear

bidirectional mic

most sensitive to sounds arriving from two direction (front and back) but rejects sounds entering sides

subcardioid

partway btwn omni and cardioid

Cardioid (unidirectional)

sensitive to sounds arriving from a broad angle in front of mic
6 dB less sensitive at sides, 15-25 dB in the rear

rejects sound from the sides less than super and hyper cardioids

Supercardioid

8.7 dB less sensitive at the sides and two areas of least pickup at 125 degrees away from front

hypercardioid

12 dB less sensitive at the sides and two areas of least pickup at 110 degrees away from the front

Guitar Mic Technique

\
what if acoustic?

mic in front of guitar amp: cardioid dynamic w/ presence peak

direct box: higher input impedance --> avoids thin/dull sound

miked and direct: run Direct In track through guitar amp simulator plug in

signal processor or stomp box

IF ACOUSTIC: pencil type condenser w/ extended frequency frequency

Direct Boxes -- what do they fix

fixes loading problem when recording direct

ground-lift switch \= prevents ground loops and hum

mixer mic inputs limit at 1500 ohms, guitar pickup \= thousands ohms \= overall \= thin/dull sound

three-to-one rule

space mics at least 3x the mic-to-source distance

- vocal mic technique
- amp mic technique

Snare Drum Mic Placement

cardioid dynamic w/ presence peak, front of set on a boom, even w/ the rim, 2 in above head, aim down, place a mic on the bottom with opposite polarity

Hi Hat mic placement

cardioid condenser mic 6 in over the cymbal edge that's farthest from the drummer, mike above aiming down, filter lows below 500 kHz

Tom-Toms Mic placement

mic toms individually or put a mic between each pair of toms, cardioid dynamic mic 2 in over the drumhead and 1 in from the rim, angled down about 45 degrees toward the head

Kick Drum Mic Placement

large-diameter, cardioid dynamic type with an extended low frequency response, place inside on a boom few inches from where beater hits

Cymbals

cardioid condenser with an extended high frequency response or ribbon mic, place overhead 2-3 ft above cymbal edges

Drum Mic: One Mic Technique

large diaphragm cardioid condenser mic and mount over the kick drum top, even with beater head, aiming snare drum

Coincident Pair

two directional mics w/ grilles touching, diaphragms one above the other, angled apart

lvl differences btwn channels \= stereo effect

Spaced Pair

two identical mics ft apart and aim straight ahead

time differences btwn channels \= stereo effect

Near-Coincident Pair

angle apart two directional mics, spaec grilles few inches apart horizontally

lvl and time differences \= stereo effect

Baffled Pair

two omni mics ear-spaced apart, separated by hard/soft baffle

lvl, time, spectral differences \= stereo effect

Vocal Mic Techniques

coincident, spaced, near-coincident, baffled pair

lead vocal: flat response condenser mic w/ large diaphragm 8 in away

on-surface: place a mic near a hard reflecting surface

sibilance

emphasis of "s" or "sh" sounds --\> strongest around 3-10 kHz

reduced by using mic w/ flat response

plosives

Sounds which release a sudden burst of air (pop sound) e.g. p,b,t

Recording Formats Timeline

1. Edison's Phonograph (1877)
2. Graphophone (mid 1880s)
3. Long Playing Records (1925)
4. Radio (early 1920s)
5. 78 RPMs (early 1930s)
6. Vinyl LP (1948)
7. 45 RPM (1949)
8. Magnetic Tape Recording (1935 intro, 1950 use)
9. Audio Compact Cassette (1963)
10. 8-Track Stereo Cartridge (1966)
11. Sony Walkman Portable (1979)
12. Compact Disc (1982)
13. CD-ROM (1986)
14. R-DAT (1987)
15. Mini Disc/Philip's DCC (1990s)
16. MP3 (1989)

Edison's Phonograph

Date
Mechanism
Impact

1877

recorded and played back sound mechanically using metal stylus and cylinder wrapped with tin foil

diaphragm's mvmts \= groove in the foil

established commercial presence

Gramophone

Date
Mechanism

mid 1880s

Wax-coated cylinder (same mechanism as phonograph)

Long Playing Records

Date

1925

Radio

Original Intended Use
Impact

originally developed for military use during WWI

1929 --\> RCA --\> modern era of music industry born

78 RPMs

Date
When did it fade from scene?
Playing Time

early 1930s
faded from scene by 1955
playing time: 3-5 mins

Vinyl LP

Date
Measurements, RPM?
Playtime
Faded from Scene?

1948

12-inch, 33 ⅓ RPM LP → much more durable than 78 RPMs

playtime: 20+ min per side

until late 1980s

45s

Date
Measurements, RPM?
Impact
Faded from Scene?

1949
33 ⅓ competitor b/c they required diff record players w/ diff speeds
early 1950s → industry came together → LPs for albums, 45s for singles
until late 1980s

Magnetic Tape Recording

Date
Mechanism
Impact

1935 intro, 1950 main use

tapes are made of powdered ferrous oxide compound bonded to long strip of tough plastic \= backing where oxide is painted + held in place w/ adhesive binder

manufactured in ¼, ½, 1, 2 in → most frequently used \= ¼ in tape
allowed for performances to be edited → allowed overdubbing, splicing → expanded creative freedom

reel-to-reel tape \= professional; difficult and inconvenient for consumers

Audio Compact Cassette

Date
Impact

1963
cassettes more reliable and less cumbersome than 8 track

8-Track Stereo Cartridge

Date
Impact
Mechanism

1966

broad success in automotive applications

single reel with two ends of the plastic recording tape joined with a piece of conductive foil tape to make one continuous loop
\-- motorized capstan in played rolled against a pinch wheel inside to pull the tape across the player's read head

Sony Walkman Portable

Date
Impact

1979

established cassette's dominance of pre recorded tape market by 1983

record labels ceased production of 8-tracks

Compact Disc

Date
Impact
Sample Rate/Bit Depth
Playback Time
Advantages

1982

ushered in digital age

sample rate: 44.1 kHz

Bit Depth: 16-bit

playback: at least 74 min

no surface noise, can skip tracks

CD-ROM

Date
Enabled?

1986

for personal computers
mid 1990s → CD-ROM's multimedia capabilities utilized

add graphics, text, video to music CDs

R-DAT

Date
Controversy?
Intended Audience
Benefits

1987

controversy: digital copying

SCMS introduced to break chain of perfect digital cloning
adopted for professional and "pro-sumer"; not consumer format

low price, enhanced digital storage capabilities

MP3

1989

compression format that shrinks digital audio files w/ negligible sound quality degradation

MP3 Player made in 1997

Analog Tape Recorders

record the audio signal as magnetic patterns that rise and fall in strength

Analog Track Layouts

Mono: 1-channel/1-Track --\> track occupies the full width of magnetic tape

Half-Track Stereo: 2-channel/2-track --\> two magnetic tracks (occupied half of tape width each) separated by guard band

Multitrack: same number of tracks as channels

Tracks v. Channels

tracks \= magnetic paths onto which the signals are recorded on a tape

channels \= number of inputs-outputs a machine has

Tape Decks

quarter-track reel-to-reel tape machines
- 1960s
- home stereo recording and playback systems
- four interleaved track placed on 1/4 in

multitrack tape machines
- 1970s/1980s
4-track, 8-track, 16-track \= 1/2 in tape

Tape Deck Transport Mechanism

three motors: feed reel, take-up reel, capstan

capstan/pinch roller \= moves tape

feed reel moves opposite to the take-up reel → keeps tape taut

tape rewind: pinch roller/capstan disengaged, more power to feed reel

Tape Editing

- Erase: pass tape under erase head --\> magnetic properties of the tape oxide coating are scrambled

- Splicing: mark off locations, take tape off head assembly, use razor blade to cut, splicing tape to join two ends, rethread tape onto deck

Connectors

XLR (male/female)

1/4-in phone jack (male/female)

Tip Ring Stereo 1/4-in

RCA Connector

1/8-in Connector

Adapters

Adapter Turnaround Coupler

Cords

Power Cable: AC extension/power cord

Speaker Cable: connects power amp to each loudspeaker

Patch cords: connect recorder-mixer to external devices

Splitter Y Cord: duplicate a single audio signal into 2 identical audio signals

Digital Recorder

store the audio signal as a numerical code of ones and zeros

Pulse Code Manipulation: signal from mixer goes through low-pass filter, filtered signal goes through analog-to-digital converter, measures the voltage of waveform, quantization

Non-Destructive Editing

only the pointers change; the data on disk is not changed/destroyed; not permanent

Destructive Edits

they write over the data on disk

Delete Noises

delete background noise (i.e. chair squeak) → don't close up the space you create after deleting

Clean-Up Tracks

cut out silence, noises → prevents leakage and tightens up sound

Duplicate Musical Parts

copy vocals from one chorus and paste them at the measures where the chorus is repeated

Replace Wrong Notes

delete a wrong note, copy an in-tune note where the wrong note was

Make Special FX

copy a syllable and paste it several times to create stuttering, copy guitar track and paste it 20-30 ms delayed in another to create stereo sound

Fade Out, Fade In

slow drop in volume to silence; fade in slow rise in volume from silence

Crossfade

fade out of one clip while fading into another; cross fade across an edit

Fix Timing Errors

visually align start times of notes in various tracks

Remove or Rearrange Song Sections

create zero crossing at edit point so that the waveform crosses the 0 dB line

Sampling Rate

rate at which the A/D converter measures the analog signal while recording

Bit Depth

determines the number of possible amplitude values we can record for each audio sample

Signal Levels Modes

RMS: readings correspond to the avg lvls \-- how loud the sound is

Peak: readings show the lvl of peaks or short transients \-- how close the signal is to clipping (always use peak)

Advantages of Good Levels

- prevent inter-sample clipping
- won't overdrive mic preamp
- create headroom for plug-ins

Level Setting

max gain until red light flashes then bring it down a little below

(-3 to -6 dBFS)

on any stem, master output, output of each plug-in