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PART 0I. TUNE IN

CHAPTER TWO

01.02

part 01. tune in28

Obviously, sound pressure waves cannot

be created where there is no atmosphere,

because there are no molecules for the source

to vibrate against. T hat’s why, to borrow the

tagline from the movie Alien:

‘In space, no-one can hear you scream.’

GOOD VIBRATIONS

Different types of sounds, such as a scream,

are characterised by different waveforms, or

usually, complexes of waveforms. In the case

of the human voice, soundwaves emitted from

the vocal chords are modulated bymovements of the mouth. We’ll talk about

waveforms in more depth shortly.

Our profoundlydeaf person feelssome

of these vibrations, and learnst o distinguish

between wavesof a higher or lower frequency

and amplitude. M eanwhile, a hearing person’s

ears translate the sound pressure wavesinto

something that the brain can recognise,

understand – and locate spatially – in other

words, hear. When we discussvolume, we are

reallyt alking about SPL (sound pressure level).

But what do we mean by waveforms,

frequencies, amplitude and so on? You already

knowpart oft he answer to this question. In

fact, frequencyisjust one characteristic ofall

typesof waves...

BASIC THEORY

So,that’swherewe’vecome from.Butwhatarethe underlying

principlesbeneathall thathistoricalinnovation?Onceyou strip

away all thel ogarithmic calculations,equationsand baffling

acronymsthatfi lltextbooksaboutsound engineering,the

underlying princip lesof sound,recording and today’sdigi tal

technologiesare simple.

Indeed,oncewe’veg rasped someofthe basics,we can

logically infer many ofthe rest.So,now it’stime for thereally big

questions.Afterwards,we’lltakea personalview ofthedig ital

age,thenmoveon tohardwareand softwarechoices.We’ll alsobe taking thepulseof theheartof digitalmusic:MIDI.

WHAT IS SOUND?

Soundraisesaclassic philosophicalquestion:doesit existif youlackthe

meanstohear it?It isknown thatprofoundlydeaf people aresensitiveto

vibrations,andthereare famousexamplesofd eafmusicians,such asthe

percussionistEvelyn Glennie.So,given thatsoundcan be meaningful to

peoplewithnoauditoryfaculty,thisgivesusaclueas towhatsoundreallyis.

Whensomething‘makesasound’,it vibratesand emitspressure

waves– periodicvariationsinatmosphericpressure –thatarereceived in

thehumanear.Thebrain interpretstheseassound,but thebody can

sensemany ofthem,and absorb all ofthem.(A soundcheckin anempty

hallhastocompensatefor thedifferentacoustic signatureofthe space

whenit isfull ofthousandsofpeople.)

Ifsomeonestandsina field and screams,theuniquevibrationsof

their vocalchordsforceair moleculestogether and propelthe molecules

away from their mouthathigh speed.Thiscreateswhatis knownasa

compressionwave,anareaof higher thannormalatmospheric pressure(butonethat’stoo small tobe measured by a barometer).

Right:Asudden noise – such as a

pers on’s scream in the middle ofa

field – propels molecules at high

speed creating a compression

wave, a ripple ofhigher than

normal atmospheric pressure that

travels awayfrom the source ofthe

sound. Volume can thus be defined

as SPL: sound pressure level.

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Above:Sound waves can be

imagined as the 3Dequivalent of the ripples we see in water, but in a

spherical form moving outwards

through space.

Below: Altho

travels in all

instruments,

other devices

direction. Plu

capture soun

direction rathe

MOVING AT THE SPEED OF SOUND

Th is is how sound waves behave in the at mosphere, except

that they move more quickly through air – at 344 metres/376

yards per second, and in three dimensions. In effect, sound

describes a sphere. So, let’s get back to our screaming person

in a field. You can now imagine the pressure waves and their

unique waveforms moving invisibly through the air – at the

speed of sound, of course – from th e person’s mouth to

your ears.

In reality, most sounds are more or less directional.

While a thunderclap might be heard equally at all compass

points from the point of origin, human voices and

loudspeakers are designed to project sound pressure waves in

a specific direction. And we can choose to listen to them, or

merely to hear them.

30 part 01. tune in

Picture a glass bowl full of water. Looking down from above,

imagine a vibrating object – an electric toothbrush, perhaps –being lowered into the cent re of the water. You know from

experience that ripples will spread out from the object towards

the edge of the bowl, and that they will increase in frequency

(there will be more of them, their production cycle will

increase) if we speed up the vibration.

Next, imagine for a moment that our circular bowl is

now a rectangular glass tank, and that the ripples are moving

in a single direction – let’s say from left to right. Pict ure

yourself looking through the side of the tank, with your eyes at

water level as the r ipples pass before you. You are now seeing

the repeating pattern of the waves created by the object

vibrating in the water. T his is a simple waveform.

Finally, keep the same view, but imagine that th e ripples

are once again moving in all directions, and that you are looking

through the side oft he circular bowl. The ripples will be

moving towardsyou, aswell asto all other pointsof the circle.

LOOKING THROUGH THE WAVE Themostcommonillustrationof simplewavebehaviour isd ropping

astoneinto calmwater,then watching ther ipples(smallwaves)fanout fromthe pointof origin.Thisis

misleading when it comesto sound,so let’s use asimilar,but moreaccurateexample.

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Above:Magnetic tape converts

electrical signals to a magnetic

fluxwhich is applied to th e oxide

on the tape. This is one process

oftr ansduction that will cause a

small amount ofdegradation each

time it is repeated on the same

analog audio signal.

THE FLAW OF ANALOGHere is an example ofth e ‘chain’of induction involved in an

average analog recording. A microphone leads sound waves

from the atmospheric into the electrical realm byturning them

into electrical signals(or radio signals, in the case of radio mikes).

Via an amplifier, magnetic tape recorders convert these

signals into magnetic fluxand store it, then reverse the process

at the playback head. At this point the energy might be

transduced again, this time by being stored in grooves cut into

a piece of vinyl. Either way, the signal is amplified electrically

at the playback stage.

Loudspeakers change the electrical signal back into a

close approximation of the original sound waves, by a process

called magnetic induction. T his causes the speaker cones to

vibrate according to the voltage levels in the signal. And your

ears turn the sound waves back into electricity again, this time

in the form of nerve impulses in the brain. Simple, isn’t it?

Th e flaw in the analog process is plain to see. It is not

that it is somehow unable to reproduce the same range of 

frequencies, the same dynamic range, as digital technology

(quite the reverse), but that there are so many stages at whichthe energy is transduced, stored, then transduced again.

At anyone ofth ese, the processis subject to degradation,

or to the inherent frailties of the transducer, the storage

medium, the amplifier or the loudspeaker. This degradation is

passed on from stage to stage and accumulates in effect.

Professional studios are on top of the problem, but you are not.

‘Hi fidelity’, or ‘hi fi’as we know it today, is merely a

vague guarantee that the chain of transduction processes will

introduce only minor departures from the integrity of the

signal. Agood hi-fi, then, will reveal deficiencies in a bad

recording, rather than compensate for them.

All of this brings us to t he exciting part for creative

people. Once sound has been turned into electrical energy,

you discover that you can change the sound in as many ways

as you can effect a change in the energy. But things get even

better once we move into the digital realm. When energy is

stored digitally, you can affect the sound in as many ways as

you can rewrite th e informatio n. You can change ‘the story’in the retelling.

So, is your creative energy up to the challenge?

32 part 01. tune in

WHAT IS ANALOG RECORDING? Analog recording is a processof transduction,and transducers

arenothing lessthan the keys to all sound recording and listening.A microphone,a loudspeaker

and your earsareall typesof transducer.Theword comes fromthe Latinpreposition trans, (a)cross,

and the verb ducere,to lead.

Literally, a transducer is a device that leads

energy from one realm into a different, but

corresponding, energy realm – in other words, itis a way of changing one type of energy into

another. In all recording techniques, energy is

changed in such a way that it can be changed back 

again when the recording is played. And the

clever part that makes it work is usually our

brightest spark: electricity.

All acoustic musical instruments, such as

flutes, saxophones, classical guitars, snare drums

and so on, are primitive transducers as well, but

most need electrical amplification or sympathetic

acoustics to be heard over any distance.

Right: Even the best loudspeakers

subject analog audioto degrada tion,

in the process ofconverting an

electrical signal into an

approximation ofthe original

sound waves.

PRODU

REAL WO

There is so

computer

onto hard

microphon

the perform

60sp roduc

whatGeorg

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34

Indigital recording,boosting decibel levelsbeyond

thereferencelevel producesdestructivedistortion;in

analog recording, it may introduce anattractive fuzziness

thatyoucanlive with.

Justthink ofthedecibelasa measureof loudness

(moreaccurately,of relative intensity) and remember touse

zeroas your referencedecib el levelwhenever youare

mixing signals,particularly when adjusting theGain oninput.

Decibel’,incidentally,means‘one-tenthof abel’. And yes,that

referstoAlexander Graham Bell– another reminder ofaudio

technology’slasting debtto thetelephoneand telegraph.

We’vealsol earned that any reproductionmethod is

areversal ofthe recording process;Edison’sPhonograph

defined thispr inciple.A microphoneturns sound wavesinto

electrical impulses;aloudspeaker turnselectrical impulses

back intosound waves.(Ifyou plug apair of headphonesintoamicrophone jack socketand shoutintooneof the

earpieces,itwill actasa microphone,albeitapoor one.)

PART 0I. TUNE IN

CHAPTER THREE

01.03

part 01. tune in

Above: When two waveforms are in

phase, such as when your left and

right speakers are playing the

same tone, the resulting sound will

double in amplitude. Ifthe two

waveforms are completely(180

degrees)out ofphase – which

would happen ifyou were to

reverse the polarityofone speaker,

for example – the resulting tones

will subtract from each other,

cancelling each other out and

producing a weak sound.

RING THOS E DECIBELS !

Wesaid earlier that youcanlogically infer many of thebuilding blocksof

audioonceyou’vegrasped someofthe basics.So,let’stestthat theory.

In analog recording,we’ve examined how sound is emitted as

wavesof pressure,and is captured aschangesin voltage,for example,

or asp hysical displacement in amedium such as vinyl.It follows,then,

that sound can be expressed,described and measured aschangesi n

atmospheric pressure,or aschangesin voltage.C ongratulations:you’ve

arrived at the decibel (dB).

Thedecibel isa logarithmic measurementof amplitude,where

sound pressureis compared to a referencepressure.This probably seemscomplicated;butall youneed toremember isthat0 dBis theHoly Grail of

therecording process;all professional mixes aredonewith referenceto it.

Modifysamples

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Right: This diagram is a basic

graphical approximation ofthe

range ofdecibels and frequency

taken up byvarious types ofs ound,

such as speech a nd music, and

where our abilityt o perceive itbegins. Note that while the human

voice has a multitude ofvariat ions,

it generallyoccupies onlya relatively

small place at the center ofour

range ofhear ing. Note the pain

threshold. 24-bit recordings have a

dynamic range of144dB.

Below: The positive and negative

peak ofa waveform ‘its peak 

amplitude’can clearlybe s een and

even manipulated in sample

editing software such as BIAS

Peak. Note that stereo sounds are

represented bytwo separate

waveforms, one for the left channel

and one for the right.

or in the Edit View Screen of a multitrack 

recording package such as Cool Edit Pro (PC).

When represented graphically,waveforms rise above and fall below an

imaginary centre line. In many packages, such

as Cool Edit Pro, you will see two distinct

waveform lines, one for each stereo channel.

Asignal’s amplitude, then, is the

distance between the positive or negative

peak and this centre line. The greater t his

distance is, the higher the signal’s amplitude

is said to be.

Th e ‘cycle’we mentioned previously

refers to the complete run-through of a

waveform’s characteristic patter n: from the

centre line through its positive peak, its

negative peak, then back again to the centre

line. Acont inuous tone is one whose cycle

endlessly repeats until the tone is switched off.

WHAT IS VELOCITY?

Speed through the atmosphere. In this case,

yards per second, although the speed of soun

measurably in warm, moist air, and decrease

(This hasimplicationsfor mixing sound in largIn normal atmospheric conditions, all

this speed. Sounds of higher amplitude migh

because they create more intense changes in

pressure, but they do not travel faster!

ENVELOPE

Th is usually refers to parameters within the

generated by musical instruments. Indeed, yo

sampler has controls that change these param

‘envelope’. T hese are nor mally the sound’s A

it hits peak amplitude); its Sustain (how long

and its Decay (how long it takes to fade to sil

amplitude). T hey may also include its Delay

inserted before the Attack); its Hold (how lo

portion of the envelope is held); and/or its R

at which the note is switched off).

36 part 01. tune in

SURFING THE SOUND WAVES Waveformsare graphicalrepresentations ofdifferent typesof signal.

Someare simple,pure-tone waves,such asa sine wave;but most soundsaremade up of complex

interactionsof differentwaveforms.(Synthesizers enable youto play withthesebuilding blocksof sound,

and construct complex soundsfrom simple components.)

Aseverysound consistsof ‘signature’waveforms,it followst hat

what distinguishesone typeof sound from another one– let’ssaya

snaredrum from ahuman voice– isrepresented bycharacteristicdifferencesin thecomponents ofeach waveform. Agood wayof 

remembering what the components of waveforms are isto

memorise the following acronym:W AVE PFH . This stands

for Wavelength, Amplitude, Velocity, Envelope, Phasing,

Harmonics and Frequency.

But what does each of these mean?

WHAT IS WAVELENGTH?

Th e physical distance throu gh a medium, such as the

atmosphere, that a soundwave travels to complete one cycle.

The term isusuallyapplied, therefore, to continuous, predictable

waveswhose cyclesare uniform and easilymeasurable.

WHAT IS AMPLITUDE?

Acomplicated way of referring to th e level of a signal – its

peak, in other words. All waveforms have both a positive and

a negative peak. Have a look at a signal in a sample-editing

package such as BIAS Peak (below) to see what we m ean,

0 Hz

120 dB

100 dB

0 dB

0 dB

0 dB

0 dB

dB

00 Hz

Music

Threshold of hearing

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