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REVOLT PRO MEDIA
Glossary - Audio Terminalogy
A
Ambience
The reverberant quality of a room.
Amplitude
The relative value of a signal, its
volume or magnitude. The height of its
waveform.
Anechoic
Without echo. Said of an acoustic which
is free field (i. e. without boundary
or reflecting surfaces), and specifically
of a room which is designed to produce
no reverb or other echo effects. This
is achieved by making the walls with
very irregular surfaces of considerable
and varying depths, in such a manner
as to ensure that (in theory) all sound
pressure waves which strike the walls
are completely absorbed. Rooms of this
type are used to test audio equipment
such as loudspeakers and microphones
and for other types of research.
Attack
Time
(1) The time taken for a musical or
other sound to reach maximum loudness
or timbre from silence. The start of
a sound. (2) Of a compressor or limiter
etc. The time the device takes to respond
to a transition in the signal level
beyond the threshold. (3) Of an envelope
generator the time taken for the envelope
to reach its maximum level from its
off or zero position. If the EG is being
used to control an amplifier (VCA or
DCA) the time taken to reach maximum
loudness from silence.
Attenuation
A reduction in the the amount of some
quality such as signal level. The property
exhibited by attenuators. The opposite
of amplification.
Audio
Frequency
The range of frequencies which can be
experienced by an average human being.
The range is defined as 20 Hz to 20
kHz for convenience but in practice,
is realistically closer to 20 Hz to
17 kHz. Dolphins are believed to hear
up to 70 kHz.
B
Bandwidth
(1) The upper and lower limits of a
range of frequencies a signal possesses,
or that a piece of equipment will pass.
It should not be confused with frequency
response, which concerns itself not
only with the upper and lower limits
but also how frequencies are amplified
or attenuated between these two points.
(2) One parameter on a parametric equaliser.
C
Concert
Pitch
Established by the International Organisation
for Standardisation in 1955, the agreed
reference frequency of 440 Hz. for the
note called middle A. Notated A=440.
Consonance
Dissonance
An aesthetic judgment of the relative
attractiveness of combinations of notes
sounded together. Consonance relates
to a more pleasant experience for the
listener while dissonance relates to
a less pleasant experience. The judgment
of whether any given interval falls
into one category or the other has been
arbitrarily applied throughout history,
with a general tendency for the progressing
acceptance of smaller intervals. The
terms are also used in a stricter sense
in theories of tonal harmony.
D
DB
SPL
A decibel based unit intend to give
an absolute measurement of sound pressure,
where 0 dB ="20µPa (micro
Pascals). The human range of hearing
is related to this scale with 0 dB(SPL)
being the threshold of hearing, while
120-140 dB(SPL) (depending on which
reference book you use) being the threshold
of pain.
Decibel
A ratio based measure of the comparative
amount of some quality, usually sound
level, power or voltage, relative to
some reference amount. It is often qualified
to indicate what property is being compared
i. e. dB(A), dB(v) etc. e. g. One might
talk about a signal to noise ratio of
80 dB(v). This would be a comparison
between the amplitude of the signal
(which we want to hear) and the noise
(which we don't). In this case the signal
voltage becomes the reference point,
(whatever the actual value was) and
would be called 0 dB(v), the noise voltage
(whatever the actual value was) would
therefore be 80 dB(v) smaller. The logarithmic
nature of the decibel allows us to compare
two values of enormously different magnitudes
with conveniently small numbers. e.
g. the limits of hearing in terms of
absolute pressure level cover the range
from 20µPa to 200,000,000 µPa.
Any arithmetic on this basis is quite
tedious. The same range expressed in
dB SPL is 0 -140 dB SPL. Much more convenient.
Dynamic
Range
The difference in signal level between
the loudest and quietest parts of a
programme, expressed in decibels.
E
Envelope
The characteristic change in amplitude
throughout time which all sounds possess.
The envelope of a sound has a number
of features: whether it sustains like
a bowed violin string; whether it decays
like a plucked violin string or a single
strike of a drum; and how quickly the
sound reaches its fullest intensity
- how the sound "attacks".
While the envelope of any specific sound
has specific characteristics determined
by the way the sound was generated,
it should be realised that real sounds
occur in real situations and the envelope
of a sound will change according to
the environment it occupies. A clave
in a cave may appear (what is the sonic
equivalent of the eye-based "appear"?)
to have a longer envelope than when
it is played in the open air.
Envelope
Generator
A device which produces a control signal
which varies in level with time. The
simplest of these (sometimes called
ADSR) has four parameters: Attack Time,
Decay Time, Sustain Level & Release
Time. Thus it has three time constants
and one level constant. Such a device
is often found on synthesisers, where
it is usually used to control the volume
of an amplifier, the cut off frequency
of a filter, or the frequency of an
oscillator. More complex arrangements
involving a series of time and level
constants are available, particularly
on digital synthesisers. These are called
multistage envelopes and may involve
eight or more parameters usually in
time and level pairs.
Equal
Temperament
A system for dividing an octave into
12 pitch steps, each of 100 cents. This
has the effect of making all semitones
equal in size. This became necessary
once keyboard and fretted instruments
became popular. It should be understood
that the note A which appears in F#
minor should have a slightly different
frequency from the note A which appears
in C major (this fine distinction is
one of the reasons that pitch and frequency
are not quite synonymous). This would
normally be dealt with automatically
by a proficient player on an instrument
with continuous pitching such as a violin.
A keyboard instrument would properly
have to be tuned to a particular key,
if music was then played in a different
key, some or many of the intervals sounded
would be flat or sharp. However since
it was not convenient to retune these
types of instruments correctly whenever
a new key was required, various compromises
were attempted. Equal temperament was
one such compromise whereby the error
was distributed equally between all
the notes. This made the performance
of music in different keys possible
on the same instrument without retuning,
in celebration of which J. S. Bach wrote
not one, but two books, each of 24 preludes
and fugues (a prelude and fugue in both
the major and minor forms of 12 keys).
F
Frequency
In audio, the number of repeating cycles
of change in air pressure or oscillations
in voltage, that occur in one unit of
time usually a second. Complex sounds
are made up of many pure tones of different
frequencies. Measured in units originally
called cycles per second (CPS), now
called Hertz (Hz). For convenience,
the human frequency range is divided
into three rough areas or bands. High
frequencies (between about 5 kHz and
20 kHz), mid frequencies (between about
200 Hz and 5 kHz) and low frequencies
(between about 20 Hz and 200 Hz).
Frequency
Response
A graph which shows how a system or
piece of equipment or even an environment
such as a room responds to different
frequencies. Ideally, for audio work
the graph should plot a flat line from
below 20 Hz to above 20 kHz. In practise
this is often not achieved, and the
line will fluctuate up and down between
these points, indicating that the equipment
or environment makes some frequencies
louder or quieter than others. Humans
have a well documented "non-flat"
response and this is the response used
to specify the dB(A) scale for determining
loudness. The term should not be confused
with bandwidth which concerns itself
only with the attenuation above an upper
limit frequency and below a lower limit
frequency and does not concern itself
with the range between them.
Fundamental
The lowest frequency partial which is
present in a (normally) musical sound.
See also Harmonic, Inharmonic.
H
Harmonic
(1) A special case of partial normally
occurring in "musical" sounds,
in which the frequency of the partial
has a simple mathematical relationship
to other partials. Generally they are
all integer multiples of a particular
fundamental frequency. See also Inharmonic.
(2) of or pertaining to musical harmony
(the juxtaposition of one note with
another or others).
Hertz
The SI unit of frequency, in particular
the number of times something occurs
in one second, abbreviated Hz. Named
after Heinrich Rudolph Hertz (1857-94).
The unit is sometimes alternatively
expressed as CPS.
Hz
See Hertz.
I
Inharmonic
A partial or sinewave component of a
sound which bears no simple arithmetic
relationship to any other partial in
the sound. See also Harmonic.
M
Microtonality
The exploitation of intervals which
lie between the semitone steps of the
equal tempered scale. This allows the
use of tunings and modes which are more
typical of non-western music. This important
and underestimated facility is at last
becoming available on synthesisers.
MIDI
An agreed standard for communication
between electronic musical equipment
such as synthesisers, samplers and other
devices such as computers. The core
function of the standard is to allow
information describing musical peformance
(which notes were played, how loud they
should be, plus articulations such as
"bending" of notes or vibrato
etc.) to be capable of transmission
from one machine to another. The recording
of such information for later replay
is called sequencing. The standard also
includes many functions which are ancillary
to this core activity, for example the
standardisation of files for sequences
(Standard Midi File) and digital audio
recordings (Sample Dump Standard) and
methods of exchanging information that
is unique to individual devices (System
Exclusive).
Mode
A simple definition of this complex
and diverse term would almost certainly
be inaccurate, while a full discussion
is beyond the scope of this glossary,
but here goes. Essentially a type of
scale. If the notes used in a melody
all appear in a given modal scale, and
if the melody begins or ends on the
base note (final) of the modal scale,
the melody is said to be in that mode.
The modes most commonly referred to
can be obtained by playing only (and
all of) the white piano notes between
certain keys and their octaves thus:
Ionian C - C, Dorian D - D, Phrygian
E - E, Lydian F - F, Mixolydian G -
G, Aeolian A - A. Modes are most commonly
encountered in folk and ethnic music.
The modern major and minor scales correspond
to the ionian and aeolian modes respectively.
So it seems that tonal music (most of
the music written in the last 300 -
400 years) is based on only two of a
number of possible scales, and it is
interesting to note that while much
European art music has confined itself
to a thorough exploration of only these
two modes, the rest of the world and
European folk musicians have been quietly
exploring all the rest and others. In
defence of the apparent narrow mindedness
of European art musicians, it must be
said that the other modes do not easily
lend themselves to the systematic and
hierarchical structures beloved of them.
Modular
Synthesiser
A synthesiser where the individual sound
generators or processors such as oscillators,
filters, amplifiers, envelope generators
etc. are physically separate units which
can, or have to be, connected together
by the user. This is usually achieved
by simply plugging a cable from one
unit's output to an input on another
or the same unit, using a patchcord.
The earliest synthesisers where of this
type and this is the origin of the usage
"patch" to describe the parameter
settings on modern synthesisers which
no longer use this arrangement. Systems
of this type where made by Moog (series
III), Roland (System 100 and 700) and
Korg (MS10, 20 etc.). These systems
were very flexible and led naturally
to creative experimentation, but were
expensive to manufacture and market.
This resulted in a newer generation
of synthesisers which had a more or
less predetermined signal path, which
were often less flexible but easier
to use. There has recently been a revival
of interest in modular synthesisers
and there are still manufacturers making
them.
Monophonic
The ability (or restriction depending
on your viewpoint) of an instrument
such as a clarinet or some types of
synthesiser to play only one note at
a time. Generally a monophonic synthesiser
will follow a rule to deal with any
occasion when two notes appear. It might
play the most recently received (remember
that in MIDI although you think you
play a chord, the notes are sent individually
one after the other sufficiently fast
(usually) that you think they sound
together), or it might play the note
with the highest pitch. Some MIDI controllers
require synthesisers that can work monophonically
across a number of channels, six in
the case of a MIDI guitar. Thus although
the synthesiser may be polyphonic it
is working monophonically on each channel
(2). If you think about it a real guitar
can be considered to be six monophonic
string instruments.
Multistage
Envelope Generator
See Envelope Generator.
N
Natural
Frequency
The frequency of vibration or oscillation
which a system (anything from a road
bridge to an violin string) will inherently
adopt according to its structure given
a suitable excitation, such as a gale
force wind or a bow. Also called the
normal mode.
Noise
A word used to describe signals which
humans consider to contain little useful
information, or which they actually
find unpleasant.
Noise waveform
Waveform
Noise spectrum
Frequency Spectrum
Hear Me (8k)
There are some synthetic types of noise
which are useful in sound synthesis
and technical equipment alignment etc.
These are called white noise, pink noise
and (the author has heard) blue noise.
White noise contains all frequencies
in equal amplitude distribution (and
the metaphor is from white light which
has a similar attribute). Pink noise
is filtered white noise (some frequencies
removed) and other colours of the noise
rainbow represent other filterings.
P
Panning
The process of controlling the relative
position of a sound in a stereo field
during mixdown or recording using a
pan-pot. Usually this is not completely
effective as the pan-pot alters only
the relative amplitude of the sound
left to right and not the crucial time
aspect.
Partial
(1) A single frequency, sinewave component
of any sound. all sounds are composed
of a number of partials. There are two
classes of partials. See also Harmonic
and Inharmonic. (2) Used confusingly
by Roland to refer to a basic sound
generator in a number of its "LA
Synthesis" products, beginning
with their MT32.
Perfect
Pitch
The ability possessed by some people
to describe one or more heard pitches
by their note names without error. This
is sometimes regarded as a magical ability
but is no more remarkable than the ability
to name a colour, and like that skill
can be learnt by most children and even
some adults. It is a rarer skill simply
because it is less practised. Some people
have a more extreme form where they
can not only name the note heard but
tell you whether it is flat or sharp.
Some even feel discomfort if it incorrect.
This "gift" is occasionally
described as absolute pitch. It seems
to be common among children with autism.
Phon
A unit of apparent sound level or loudness
which takes account of the variable
human sensitivity to different frequencies.
Pitch
Broadly speaking the musical equivalent
of the technical term "frequency",
although they are not exactly synonymous.
This is usually because pitch is also
used as a synonym of note name. So one
musician might ask another "What
pitch is that?" and be satisfied
with the answer "A", whereas
the answer "440 Hz" would
probably dismay.
Propagation
Movement through a material. e.g. the
movement of sound waves through air.
Pulse
Wave
A family of geometrical waveforms typically
generated by an oscillator.
Pulse waveform
Waveform
Pulse spectrum
Harmonic Structure
Hear Me (8k)
They are all rectangular in shape, i.e.
the only angle which occurs is 90°
between immediate, vertical transitions
and horizontal "high" or "low"
levels, but they have any possible mark/space
ratio. Square wave is a special case
of pulse wave where the mark/space ratio
is 1:2. The harmonic partials present
are determined by the mark/space ratio
such that the harmonics which are multiples
of the rightmost number in the ratio
will be absent. Thus a pulse wave with
a mark/space ratio of 1:3 will not have
the 3rd., 6th. or 9th. etc. harmonics.
Other harmonics will be present at varying
amplitudes depending on their proximity
to the "dead" or absent harmonics.
When the ratio becomes very large i.e.
the pulse becomes very narrow, the timbre
becomes correspondingly thin and nasal,
rather like an oboe or harpsichord.
See also Ramp Wave, Sine Wave, Square
Wave, Triangle Wave.
R
Ramp
Wave
A geometrical waveform typically generated
by an oscillator.
Ramp waveform
Waveform
Ramp spectrum
Harmonic Structure
Hear Me (8k)
It resembles a series of ramps placed
nose to tail. It has all possible harmonic
partials (odd and even numbered). The
amplitude of each harmonic is the reciprocal
of its number in the series (i.e. the
5th. harmonic is a 5th. the amplitude
of the 1st.) It has a very powerful
and brassy timbre. It sounds the same
whether the ramp rises left to right
or falls left to right. Sometimes called
sawtooth. See also See also Pulse Wave,
Sine Wave, Square Wave, Triangle Wave.
Reverberation
A complex of many reflected sounds occurring
in an enclosed space such as a building
or cave. The effect is often confused
with echo which, strictly, is a discrete
repeat of a sound event. Reverberation
occurs to some extent in any place where
a sound can occur, but is most noticeable
in very large places with many hard
reflective surfaces which are at complex
angles to one another, such as large
churches etc. Most people are able to
recognise particular types or reverberation
and can associate these with imaginary
rooms of varying sizes. Devices for
the artificial creation of reverberation
( sometimes called "room simulation")
have been available for some time. Initially
based on electromechanical devices such
as reverb springs or reverb plates,
these are now usually digital devices.
Several distinct phases are observed
in the evolution of a reverberative
sound and these include pre delay, early
reflections, high & low frequency
damping, decay.
Reverberation
Time
Also call Rt60. In a reverberant environment,
this is the time a sound event will
take to decrease in amplitude by 60
dB(SPL). In general bigger spaces will
have longer Rt60 times than smaller
spaces, however there are a number of
other factors to be taken into account
such as the damping effect of furniture,
curtains or even people.
S
Sawtooth
Wave
See Ramp Wave.
Sine
Wave
A geometrical waveform having a curve
defined by the function y= sin x.
Sine waveform
Waveform
Sine spectrum
Harmonic Structure
Hear Me (8k)
In theory there are no other partials
present and it can therefore be considered
as the basic component from which (by
combination) all other waveforms are
made. It is the basic building block
of all sound. Sometimes used quite incorrectly
to describe pure tones irrespective
of waveform. See also See also Pulse
Wave, Ramp Wave, Square Wave, Triangle
Wave.
Sound
Wave
See Wave.
Spectrum
The range of frequencies or partials
of an audio signal.
Spectrum
Analyser
A device for displaying the relative
amplitudes of a range of frequencies
or partials in an audio signal.
Square
Wave
A geometrical waveform typically generated
by an oscillator.
Square waveform
Waveform
Square Spectrum
Harmonic Structure
Hear Me (8k)
It is a special case of pulse wave,
where the mark/space ratio is 1:2. It
has only the odd numbered (1, 3, 5,
7, etc.) harmonic partials. The amplitude
of each harmonic is the reciprocal of
its number in the series (i.e. the 3rd.
harmonic is a 3rd. the amplitude of
the 1st.). It has a buzzy but mellow
timbre very similar to that of a clarinet.
See also Pulse Wave, Ramp Wave, Sine
Wave, Triangle Wave.
Synthesiser
(1) An electronic device for making
sounds, in which the shape and method
of construction have little effect on
the nature of the sound produced. This
wide definition includes: Electronic
organs, samplers, drum machines even
radio sets etc. as well as those devices
which are more immediately recognised
as synthesisers. Some devices, such
as the Thérémin do owe
their sound, in part, to their construction,
and may be considered somewhat "grey"
in respect of this definition. (2) A
specific case of (1) above, equipped
with oscillators, filters, amplifiers
as well as modulation sources. Either
with a predetermined or more or less
programmable audio and control signal
path, which can be used as a musical
instrument or for sound effects. The
oscillators may include the ability
to replay digital recordings of sounds,
and the whole or part of the system
may be implemented using digital or
analogue technologies.
T
Timbre
The quality of a sound determined by
its partial structure, that is the relative
frequencies and amplitudes of the various
sinewaves which collectively make up
that particular sound. It is more or
less synonymous with "tone".
It is this quality which allows you
to distinguish between a flute and an
oboe playing the same pitch at the same
volume.
Triangle
Wave
A geometrical waveform typically generated
by an oscillator.
Triangle waveform
Waveform
Triangle spectrum
Harmonic Structure
Hear Me (8k)
It is triangular in shape and comprises
the same sequence of only odd numbered
(1, 3, 5, 7, etc.) harmonic partials
as the square wave, but as the amplitude
of each harmonic is the reciprocal of
the square of the harmonic number (i.e.
the 3rd. harmonic is a 9th. the amplitude
of the 1st.), the sound is much weaker
or more mellow. See also Pulse Wave,
Ramp Wave, Sine Wave, Square Wave.
W
Wave
Waveform
A cyclic propagation of energy through
a medium at a constant velocity. e.
g. sound pressure waves through air,
or a diagram of such oscillations. Also
refers to the appearance of the oscillating
voltage of an audio signal on an oscilloscope.
See also Pulse Wave, Ramp Wave, Sine
Wave, Square Wave, Triangle Wave.
Wavelength
The distance between two identical points
on a waveform i.e. one cycle of the
waveform, or the spatial distance between
two identical points of an electromagnetic
or sound pressure wave which have the
same phase. In high frequency waves,
there are more cycles in a given unit
of time than there are in low frequency
waves, this means they are closer together
and consequently the wavelength of a
high frequency is shorter than that
of a low frequency. The wavelength of
an given frequency can be determined
by dividing the speed of propagation
of the wave by its frequency. For electromagnetic
waves this is c/f, where c is the velocity
of light and f is frequency, this gives
a result in metres. For sound pressure
waves it is approximately 334 m/s divided
by the frequency in Hz, so that audio
frequencies have wavelengths in the
range from 16 metres to 1.6 centimetres.
White
Noise
A signal which contains all possible
audio frequencies in equal average amplitudes.
Useful for testing equipment. |
