TA212 The Technology of Music Steve Wells. Producing Musical Sounds TA212: Block 3, Chapter 1

TA212The Technology of Music

Steve Wells

Producing Musical Sounds

TA212: Block 3, Chapter 1

TA212 - Block 3 - Chapter 1 - Producing Musical Sounds

Musical Instruments

instrumentsstrings

wind

woodwind

brass

plucked

bowed

percussion

tuneduntuned

electronicstruck

flute clarinet

keyboard

tuba

recorder

trumpet

piano

trombone

guitarharp

violin

cello

side drum

tom tom

xylophone tubular bells

synthesiser


Musical Instruments

• Something which produces sound– Compressions and rarefactions in the air

• Predictable output– Pitch– Volume– Rhythm

• Controllable by a player


Sound Production

• Need to be able to put energy into the system (excitation)– No energy – no noise!

• Something to resonate– Primary vibrator provides pitch

• String, air column– Secondary vibrators

• The rest of the instrument


Sound Excitation

• Putting in energy to make a sound– Blowing into a wind instrument– Plucking a string– Bowing a string– Beating a drum

• Energy in a burst– Transient sound

• Energy continuous– Sustained sound


Nodes and Antinodes

• Waves can “interfere” producing locations where there is no change

• These locations are fixed despite the fact that the waves are moving

• A place where Nothing is changing is called a Node• An Antinode is where something is changing


Types of Node

• A place where Nothing is changing is called a Node• Two types of Node:

– A Pressure Node occurs where there is no change of pressure• for example, at the open end of a wind instrument

– A Displacement Node occurs where there is no displacement (movement) of the vibrating medium• for example, at the bridge of a stringed instrument


Standing Waves

• The sequence of nodes and antinodes form a standing wave

• When a string is vibrating:

displacement node

displacement node

displacement antinode

A NN


Standing Waves

• The sequence of nodes and antinodes form a standing wave

• When an air column is is vibrating:



displacement node

A AN

Woodwind Instruments



Wind Harmonicsopen pipe stopped pipe

NOTE: A conical pipe (such as an oboe) behaves like a pipe open at both ends


“Bernoulli” Principle

Air blowing over a surface creates suction

…either the air moves... …or the surface moves!


Oboe Reedair air air


Recorder Mouthpiece

air

air

Suction due to the Bernoulli Effect.

The air stream passes to one side of the edge, is sucked onto the edge and overshoots.

This repeats...


Wind Pitch

• Length of the pipe determines the pitch– (also temperature)

• Change pitch by:– Changing the length

• Brass instruments– Finger holes

• Woodwind


Wind Pitch

• Pitch of a pipe depends on two things:– Length (L) : shorter = higher– Speed of Sound (v) : higher temperature = higher

• For a pipe open at both ends:

• For a stopped pipe (open at one and closed at the other):

L

vf

21

L

vf

41


Fingerholes

Effective length depends on the position and size of the hole


Fingerholesphysical end of the pipe

displacement antinodes

no fingerhole

small fingerhole

large fingerhole

The displacement antinodes are at different possible positions due to different end effects.


Recorder Mouthpiece


Due to end effects, the displacement antinode is effectively inside the air channel

air


End Correction

• Effective length of a pipe is greater than the physical length of the pipe.

effective length

physical length


End Correction

radius (r)

end correction (e)

re 6.0

TA212 - Block 3

Question: Length of a Pipe

A pipe stopped at one end sounds the note A4 (440Hz) as its first harmonic. If the pipe has a diameter of 20mm, what is the physical length of the pipe?

Assume the speed of sound to be 340m/s.

Brass Instruments


What is a Brass Instrument

• Not always made of brass!!• Key idea is the way the sound is made

– Lip reed– Players lips vibrate within the mouthpiece to excite the

air column– Similar to the way a reed excites the air column in and

oboe or clarinet

TA212 - Block 3 - Chapter 3 - Brass Instruments

Parts of a Brass Instrument


Types of Brass Instrument

• Mainly Cylindrical– Natural Trumpets and Trombones

• Mainly Conical– Horns

• Combination of Cylindrical and Conical– Trumpet– Cornet

(A Cornet has a longer conical section than a Trumpet)


The Air Column

• The bell is open• The mouthpiece behaves like a closed end• However...

– Fundamental not used (usually out of tune)– The flare on the bell raises the pitch of the lower

harmonics– The mouthpiece lowers the pitch of the upper

harmonics• The effect is to get an almost complete harmonic

series (the fundamental is missing)


Tuning

• Harmonics are used more than with woodwind– Bugle only uses harmonics

• Tuning – Slide– Valve– Finger holes

• like woodwind• not used in modern orchestral instruments


Valves


Stringed Instruments



String Harmonics

• Many different standing waves • The sounds they produce are the harmonics of the

string.


String Pitch

• Pitch of a string depends on three things:– Length (L) : shorter = higher– Tension (T) : tighter = higher– Mass per unit length ( ) : lighter = higher

TA212 - Block 3

Question: String Tension

A Fender Stratocaster has a string length of 648mm. The sixth string (lowest pitch) has a mass per unit length of 6.79x10-3 kg/m. It is tuned so that its first harmonic is E2 (82.4Hz).

What is the tension in the string?

f1 frequencyT tensionL lengthµ mass per unit length

Violin Family

• Many medieval instruments were bowed– Rebec– Vielle

• The modern violin appears in late 17th century• Four sizes

TA212 - Block 3 - Chapter 3 - Stringed Instruments

Lowest note Tuned in

Violin G3 Fifths

Viola C3 Fifths

Cello C2 Fifths

Double Bass E1 Fourths

Violin Bridge


Lutes and Guitars

• Descended from arabic instrumets– Through Moorish Spain or, perhaps, the Crusades– “Lute” comes from “al‘ud”

• Plucked and Strummed• Strings stretched along a neck

– Usually fretted• Many variations throughout the Middle and Far East

– Long and short necks– “2” to “12 or more” strings


Classical Guitar

• Modern form developed in 19th

– Torres developed the larger body and fan strutting– Tarrega and, later, Segovia showed what the

instrument was capable of• Six strings

– E3, A3, D4, G4, B4, E5


Percussion


TA212 - Block 3 - Chapter 5 - Percussion

Drum Vibration Modes


Drum Frequencies

1.591 2.13

2.29 2.65 2.91


Other Drums

• Bass Drum– Two heads– Often one head is tighter than the other so that the

frequencies do not correspond– Untuned

• Snare Drum– Wires across one head causes a rattle as the head

moves


Simple Gongs and Cymbals

• Modes of Vibration similar to a circular drum skin• Low frequencies dominate first, then higher

frequencies take over• Untuned


Circular Plate Vibration Modes


Circular Plate Frequencies

1 3.912.331.73

Oriental Gong

• Shape forces the first two harmonics to have a frequency ratio of 2:1

• Other harmonics effectively not present

• Tuned



Vibrating Bars

• Glockenspiel, Xylophone etc


Vibrating Bars


Vibrating Bars

The instrument is “tuned” because felt supports go here to damp all but the fundamental mode of vibration

TA212 - Block 3

Question: Rectangular Bar

A glockenspiel bar is made out of steel whose Young’s Modulus is 201x109 N/m2 and whose density is 7800 kg/m3. The bar is 5mm thick and 111mm long.

What frequency will it sound?

21 03.1L

tEf

f1 frequencyE Young’s modulus densityt thicknessL length


Percussion Pitch

• Modes of vibration do not form a harmonic series• No well defined pitch, but...

– Timpani• Air damping within the instrument shifts the modes of

vibration to produce a harmonic series– Glockenspiel

• Supports damp out the unwanted modes of vibration– Oriental Gong

Keyboard Instruments


TA212 - Block 3 - Chapter 6 - Keyboard Instruments

Keyboards

• Standard interface to many different ways to make a sound– clavichord– harpsichord/virginal/spinet– piano– organ– piano accordion– electronic keyboard– celesta


Clavichord

• Unfretted Clavichord - one string for each note• Fretted Clavichord - several notes on each string

fulcrum

tangent

bridge

damping


Plucked Strings

Virginal

Spinet

Harpsichord


Piano

• Hammers hit the string• The hammer needs to:

– hit the string at a controllable speed– have a clean rebound– not hit the string twice

• Modern mechanism invented by Cristofori in 1720


Piano Key Leversforce

effectf e

force

effect

f

e

effect

f

e

forcefe

factor speed


Cristofori Action


Organ


Organ

air in

valve

tracker

pipe

windchest

key

roller


Organ Stops

• An Organ Stop selects a bank of pipes• The length is an indication of pitch, not physical

length

– 8ft is normal pitch (A4=440Hz)

– 4ft sounds an octave higher• A stop labelled “8ft stopped”

– normal pitch made with stopped pipes– NOT 8ft pipes stopped to produce the effect of 16ft

pipes.

TA212 - Block 3

Question: Organ Stops

A pipe organ is tuned in concert pitch. The key normally sounding the A above middle C (A4) is pressed.

What note will sound when each of the following stops are used.

8’ diapason4’ diapason16’ stopped

Why will the tone of the 16’ stopped pipes differ from the others?

The Voice


TA212 - Block 3 - Chapter 7 - The Voice

Anatomy


Voice and Clarinet

sound source pitch timbre

clarinet reed air column fixed

voice vocal folds vocal folds Variable(vocal tract)


Graphic Equaliser

• The vocal tract can emphasise different frequencies

• Like a graphic equaliser…• Different vowels are

produced by emphasising different frequencies


Vowels

• Shape of the vocal tract

• Each shape emphasises different frequencies• The frequencies which are emphasised are called

Formants


Spectrogram

time

freq

uenc

y formants


Formant Chart

first formant

seco

nd f

orm

ant • Vowels can be

characterised by the frequencies of the first two formants


Singer’s Formant

• Formants pulled closer together create an increase in loudness– not more energy– more efficient use of existing energy

• Distorts the vowels– consonants become important for intelligibility

Electronic Instruments


TA212 - Block 3 - Chapter 8 - Electronic Instruments

Types of Electronic Instrument

• Electroacoustic– sound source is mechanical (string of electric guitar)

• Electromechanical– replays physical representations of sounds (Hammond

organ)• Electronic

– sound is created from an electronic circuit (synthesiser)


Electromagnetic Induction

• Given any two, the third is produced

electricity + magnetism = motion (electric motor)

magnetism + motion = electricity (generator)

electricity

magnetism motion


Electric Guitar

• Electroacoustic• Electromagnetic induction

– “movement + magnetism = electricity”


Hammond Organ

• Electromechanical• Electromagnetic induction

– “movement + magnetism = electricity”– the lobes on the spinning wheel disturb the magnetic

field creating a current in the wire

magnetspinning wheel

wire


Moog Synthesiser

• Electronic• No moving parts!• Analogue


BBC Radiophonic Workshop

TA212 The Technology of Music

Contacting Me

• Phone

01454-850379• Email

[email protected]• Web

http://www.stevesphotosite.co.uk/ta212

TA212 The Technology of Music

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TA212 The Technology of Music Steve Wells. Producing Musical Sounds TA212: Block 3, Chapter 1