The

Physics of Sound

Mark Anthony Yulo, AES, ASA
Audio Solu:ons Philippines

SOUND

1. a wave motion in air or other elastic media (stimulus) or

as that excitation of the hearing mechanism that result in
the perception of sound (sensation).

2. vibration transmitted through a solid, liquid, or gas;

particularly vibrations composed of frequencies capable of

being detected by ears and arrives at the ear in the form
of periodic variations in atmospheric pressure called
sound-pressure waves.

Amplitude

- Determines how loud a signal is. The bigger the

amplitude, the louder the sound.
Expressed in terms of voltage/current and sound
pressure level, (eg. dBu, dBSPL)

AUDIO LEVEL RATINGS

Peak Level
dened as the maximum level required over a given >me interval

RMS Power (Root Mean Square ) Level

Useful in describing the energy of a complex waveform or a sine wave

DYANAMIC RANGE AND HEADROOM

The Inverse Square Law

describes the rela>onship between sound pressure level and distance from the source
States that the intensity of sound varies with the square of the distance, for each doubling of
the distance from the source, the measured sound pressure will drop by 6 dB.

Frequency
- it specifies the number of waveform repetitions per unit of

time (usually one second)

- the number of cycles that pass a set point in a second or the
rate of air pressure fluctuation
- measured in Hertz (Hz) or cycles per second (cps).

Human Frequency (AUDIO) Range:
- Normal range for human ears, although not everyone
(especially the elderly) will hear to the extremes of this
range.
20
25
31.5
40
50
63
80
100
125

160
200
250
315
400
500
630
800
1000

1250
1600
2000
2500
3150
4000
5000
6300
8000

10K
12.5K
16K
20K

FREQUENCY RESPONSE CURVE

- The charted output of an audio device. This curve is used to
graphically represent how a device will respond to the audio
spectrum and, thus, how it will affect a signals overall
sound.
- The measure of any system's spectrum response at the
output to a signal of varying frequency (but constant
amplitude) at its input.

Velocity
Refers to the speed of travel of the sound wave. This varies
between mediums and is also dependent on temperature.
In other materials, the speed of sound can vary quite
substantially. The following table shows the speed of sound
in a number of different materials.

Material

Air

Steel
Timber
Brick

Speed of Sound (m/s)

343
6100
5260
3650

Speed of sound through materials at 20 C.

Phase

Phase is the >me rela>onship of a sound wave (audio signal) to a know

>me reference, usually expressed in degrees ( ).
Described as a >me delay between two or more waveforms.
Phase must be controlled since it aects how sounds add together.

REFLECTION

Much like light waves, sound

reflects of a surface boundary
at an angle that is equal to
(and in an opposite direction
of) its initial angle of
incidence.

Single-planed, solid,
Smooth surface

Concave surface

Reverbera>on Time

The hanging on of the sound in a room aYer an exci>ng signal has been removed.
An important characteris>c of an enclosed space for speech or music; oYen
perceived by a listener as adding fullness to the original sound.
Con>nued mul>ple reec>ons, consis>ng of direct sound wave and reected
waves arriving at dierent >mes
the >me required for the sound pressure level in an enclosed space to decrease
60-dB.
Reverbera:on Time (in Seconds)
PROGRAM
0.8 1.3

1.4 2.0

2.1 3.0

Op:mum

Speech

Good

Fair - Poor

Unacceptable

0.8 1.1

Contemporary
Music

Fair Good

Fair

Poor

1.2 1.4

Choral Music

Poor Fair

Fair Good

Good Fair

1.8 2.0+

The Microphone
Microphone converts acoustic energy
Into mechanical energy into
electrical energy
There are two critically important factor involved in capturing
sound using a microphone.

Where we place the mic in relation to the sound source

The acoustical environment in which we choose to
record the sound source

Moving-Coil Mics

Dynamic Microphone:

Involves a coil of wire attached to a diaphragm and

suspended between the poles of two magnets. As the coil
cuts through the magnetic field tiny electric currents are
generated within it which relate directly to the sound waves.

1.
2.
3.
4.

Live situations.
Very useful in the studio.
Durable of all the mic types.
Also withstand the most volume before they distort within their
own circuitry.

Condenser Microphones
Relies on capacitance the ability to store or pass an electric charge.
On top is a very thin metal or a conductive plastic diaphragm which
moves at a distance from a fixed metal back plate. These two form the
plates of a condenser.

1. Most accurate.
2. Respond to fast attacks.
3. Add the least amount of tonal coloration.

Preferred when recording acoustic guitar , acoustic piano, vocals, real brass,
real strings , woodwinds, percussion, and acoustic room ambience.

TYPES OF PICK-UP PATTERN

131 Cardioid

105 Hyper Cardioid

360 Omni - directional

115 Super Cardioid

90 x 90 Bidirectional

Shotgun

FREQUENCY RESPONSE CURVE

CHOIR
MUSICAL
INSTRUMENT /
CHOIR

XY Configuration

MICROPHONE TECHNIQUES
For Guitar Amplier

Snare, Kick, X-Y

1. Two cardioid condenser microphones in a

traditional X-Y configuration above kit.
2. One cardioid moving-coil mic inside the kick.
3. One cardioid moving coil mic from about 2
above the top head.
Close-mike Technique: Snare, Kick, Toms, X-Y
1. Two cardioid condenser microphones in a
traditional X-Y configuration above the kit.
2. One cardioid moving-coil mic inside the kick.
3. One cardioid moving coil mic about 2 above the
head.
4. One cardioid moving-coil mic pointed at the floor
tom.
5. One cardioid moving-coil mic aimed between the
upper two toms and positioned so that the two
drums are balanced and blended.

21

TYPES OF CONNECTORS
RCA

XLR (Balanced)

Mini Plug (1/8-inch)

Phone Plug (1/4-inch)

Speakon connector

mobile no. 09228644106

23

TYPES OF SIGNAL LEVELS

Microphone Level Connec>ons

Low voltage, usually in the range of mV,

(0.0001 V), 150 (Pro), 50 k (Consumer)
Needs shielding to prevent electrosta>c pickup, external magne>c
elds such as transformers, motors, uorescent lamp ballasts, high
current wiring

Phono Level

about 0.0001 V, 47 k

Instrument Level

About 0.005 V, 50 k

Line Level

Professional Level: 1.228V, 600

Consumer Level: 0.75 V, 10 k

Speaker Level

Level: 5 to 200 V (Power Amp-dependent), 4-16

 Main L/R Out

Stereo Input

Direct Out

Insert Point

Line In

Mic In

Mixer Features
Insert Point
Many mixer and console
designs provide a break in the
signal chain that follows after
the equalizer. At this point, a
direct send/return or insert
point (often referred to simply
as direct or insert) can be
used to send the strips line
level audio signal out to an
external processing.

26

The Controls

+48v or Phantom Power

Some microphones, known as condenser mics, require
bajery power to operate. Alterna>vely the power may be
provided by the console. This is known as phantom power
and runs at 48vDC. Simply press Phantom Power any
condenser mics connected will operate without the
need for bajeries.

HPF (High Pass Filter)
As the name suggests
this switch cuts out the
very lowest frequencies
of a sound allowing the
higher frequencies to
Pass Through.

The Controls
EQ Sec:on
Allows you to change the tone of the sound on each input.

An EQ is normally split into bands, which control a range of frequencies,
in a similar fashion to the treble and bass tone controls on your Hi-Fi.
Indeed a simple 2 band EQ is lijle more than an input treble and bass
control. The more bands an EQ has the more sophis>cated it is.

Auxiliary Sec:on
Typically, these controls have two func>ons:

1. Create separate musicians "foldback" mixes in the studio or on stage.

2. To control the levels of eects such as reverb from external eects units
that have been added to the input signal,

The Controls

Pan (Panoramic Control)

This determines the posi>on of the signal within the stereo mix image or
may be used to route (send) the signal to par>cular GROUP outputs as
selected by the ROUTING SWITCHES.

Solo (PFL and Solo in Place)
The PFL solo switch allows you to monitor an input signal independently of
any other instruments that have been connected, which is useful for
troubleshoo>ng, or seong an instruments Input Preamp Gain and EQ
seong.

Mute/Channel On-O Switch
This turns the channel on or o and is useful for isola>ng the channel when
not in use or pre-seong channel levels which may not be needed un>l later,
ie: theatre scene seong or support acts/performers.

Fader
This determines the level of the input signal within the mix and provides a
visible indica>on of channel level.

The Controls
Rou:ng

By selec>ng the rou>ng switches the input signal is sent to a choice of the
mixers outputs - typically the main mix outs or the group outputs.

The switches are used in conjunc>on with the PAN control to route the signal
propor>onately to the leY or the right side of the mix or to odd/even groups/
subs if PAN is turned fully leY or right.

SUBGROUPS

These allow the logical assignment of groups of instruments or vocalists so

that they may be controlled by just one pair of faders, or even a single fader,
once individual instruments rela>ve levels have been balanced.
They also act as addi>onal outputs with separate volume/level controls
ideal for speaker lls or recording a number of instruments to one tape track.

Mix Outputs

Mix outputs provide leY and right level control of the nal stereo mix.
Many consoles feature mix insert points too, allowing the connec>on of
signal processors across the whole mix.

The Controls (A Descrip>on)

THE MASTER SECTION

Aux Masters
These govern the overall output levels from the auxiliary outputs and therefore
the amount of signal going to an eects unit or a musicians foldback mix.

AFL
Allows monitoring of the actual signal leaving the Aux Masters.

Meters
Normally they show mix output levels. When any Solo bujon is pressed, the
meters automa>cally switch to show the solo level. They provide visual
indica>on of whats going on in your mixer.

These allow signals from external equipment, such as eects
units, to be returned to the mixer and routed to the stereo
Mix or Groups, without using up valuable input channels.

THE EQUALIZER
EQUALIZERS are used for cutting or boosting certain
frequencies.

Parametric Equalizer

which adjust three parameters: frequency, boost/cut and Q

(bandwidth). These equalizers are often found built into each
channel in mixing consoles, but are also available as separate
units.

Frequency Filters

Low Shelving

Peaking Filter
(low-mids & mid-highs)

High Shelving

THE GRAPHIC EQUALIZER

have faders which resemble a frequency response curve plotted
on a graph. Sound reinforcement systems normally use
graphic equalizers designed on one-third octave centers .

Audio Frequency
Sub-Divisions

Very Low Bass Range (20-40 Hz)

Bass Frequency Range (41-160 Hz)
Lower Mid Frequency Range (161-315 Hz)
Mid Frequency Range (316-2500 Hz)
Upper Mid Range/ Presence (2500-5000 Hz)
High Frequency Range/ Brilliance (5-10 kHz)
Extreme High Frequency Range (10-20 kHz)

The Cross-Over System

Cross-over Network is an electronic circuit that divides the audio
spectrum into individual frequency ranges before sending them to
specialized speakers, such as woofer and tweeter.
Cross-over Frequency is the frequency at which the high frequencies
are routed to the tweeter and the low frequencies are routed to the
woofer.

Types of Cross-over

 Types of Passive Cross-over

www.audiosolutionsph.com

920.41.03

Active Cross-over (Electronic Cross-over)

They are designed to be inserted before the amplifier in the signal chain.
A bi-amplified two way speaker system is more efficient than a passive two
way speaker system because there is no insertion loss.
Headroom is increased since power is supplied by dedicated amplifiers
between components.

Bi-Amp

www.audiosolutionsph.com

Tri-Amp

920.41.03

Audio Mixing Techniques

Using PEQ, Dynamics Processor & Eects Processor

Mixing is like Sculp>ng

Mixing is a deduc>ve not addi>ve

Recognizing the Frequency of Sounds

A sound operator should learn to recognize the frequency of
sounds so you are able to quickly and correctly adjust
equalization when there is a problem
(i.e. feedback, hollowness, nasal sound, boomy, etc.)

RANGE

DESCRIPTION

EFFECT

16 60Hz

Sense of power;
Felt more than heard

Too much makes the music

sound muddy

60 250Hz
Bass

Contains fundamental notes of

Too much makes the music
rhythm sec>on; makes music fat or sound boomy
thin

250 2kHz

Contains the low order of

harmonics of most instruments

Boos>ng 500 1kHz sounds

hornlike; 1 2kHz sounds
Tinny

2kHz 4kHz

Contains speech recogni>on

sounds like m, b and v

Too much causes listener

fa>gue

4kHz 6kHz

Presence

Responsible of clarity and

deni>on of voices and
instruments

Boos>ng makes music seem

closer

6kHz 16kHz

Controls brilliance and clarity

Too much causes vocal

sibilance

Sub-Bass

Low-Mids

High-Mids

Brilliance

Compressor

q Used to maintain an
average signal level by
automatically reducing
the level of louder sound.
q Signal compression is
necessary because the
dynamic range of
equipment may be
smaller than that of the
signal and cause
distortion, clipping, or
even equipment damage.
q When the signal is
compressed, there is a
smaller difference
between the volume of
the loudest and softest
sounds.
q The content can still
sound like it's louder or
quieter but actually have
pretty much the same
volume.

COMPRESSOR PARAMETERS

Threshold
determines at what minimum sound pressure level the compressor
should start compressing.
Ratio
This control determines the slope of the input-to-output gain ratio. In
simpler terms, it determines the amount of input signal (in decibels)
thats needed to cause a 1-dB increase at the compressors output
Attack
determines how long the compressor will wait before turning down the
volume on a loud sound. Attack time is usually within the range of
microseconds.
Release
Similar to the attack setting, release (which is calibrated in
milliseconds) is used to determine how slowly or quickly the device
will restore a signal to its original dynamic level once it has fallen
below the threshold point (defined as the time required for the gain to
return to 63% of its original value)
Output gain
This control is used to determine how much signal will be sent to the
devices output. Its used to boost the reduced dynamic signal into a
range where it can best match the level of a medium or be better
heard in a mix.

LIMITER
A limiter is essentially a compressor with the most
extreme setting in effect, and sets a sound level
ceiling on a signal instead of a slow curve.
Limiters suppress very loud pops (such as when
unplugging a guitar or dropping a microphone)
which could damage the audio system.`

A noise gate sets a

threshold where if it
Is any quieter it will
not let the signal
pass and if it is
louder it "opens the
gate.
Thus the noise gates
functions are very
much opposite to
those of a
compressor.
Noise gates are
useful for
microphones which
will pick up noise
which is not relevant
to the program

Other eects and accessories

Reverberation, Echo and Delay (audio effect) effects

are widely used in sound reinforcement systems to give the
effect of natural reverb.

Less commonly, modulation effects such as Flanging and

Phaser (effect)s are applied to some instruments for an
unusual sound effect.

The Exciter (effect) "livens up" the sound of audio signals by

applying dynamic equalization, phase manipulation and
harmonic synthesis of (usually) high frequency signals.