© Envelopes
- Other Factors Determining a Sound
--
'
Besides the three basic elements
of
sound already explained, pitch, sound volume and timbre, there
is
another
important factor~ which de
term
ines a sound. This
is
the
variation
of
the' sound over time. More precisely,
it
is
the variation
of
each-
of
the three
el
ements lover time from \ he beginning
of
~thp
sou
1d up
to
the
point
in
time where
it
disJ ppears completely. If aiviolin
is
played-with-a-bo~ ~fo
r-i
nstarJ,ce, ;
<>
li,
n
.sl
volume usually
increases gradually while
the
timbre and pitc~ also change slightly. _
li
he~iu;hanges ovJ rTtime are what deter-
mines the characteristic timbre
of
a
vioUn
. On the
other
hand, if the sound
of
a piano were l o continue with-
out
decaying, it would
be
very difficult
to
disti~guish it from the the sound
of
j a
1
flute. These variations over
time are called envelopes. Envelopes expressed graphically
su
ch
as
those
in
tlie diagrams, below are called
envelope curves.
Envelope
Curves
of
Various
Instruments
(Sound Volume)
Volume
I
I
I
Violin
I
Volume
Time
I
I '
The
change
of
volume over time c
/l
n also be
1
callea ·ari-e nve,lope.
/
h.'J
Volume
Time
Time
Remember
1-------~
-=--
---------~----,-------------
...
-
c..
The
changes over time
of
pit
~h, volume and timbre are called envelopes. Envelopes are
among
the
most important factors determining a sound.
"'(,
<f)
Basic Principles
of
An~l_og
Synthesiz_e__r
Structure
I
ll
1
#
JI
' : d t J j
..,.J
. t • I
When
people talk
about
synthesizers, you
will
often hear expressions such as VCO and VCF. Many who
have
heard
~uc
m .. difficult words
will
ther
dfore find it difficult
to
approach synthesizers,' belli
vi
ri'gl they are
too complicateq.
Act
\J
ally, though, synthesi,zers are
not
that
difficult
to
un g
erstanq
at
all. , r
Analog
synt
hesizers -i~ general consist of various blocks which correspond
to
the three major elements
of
sound and
the
envelopes explained above.
'
•
VCO
(Voltage Controlled Oscillator)
This circuit corresponds
to
determines the pitch
of
a sound by controlling voltage. This block
is
also used
to
_create basic waveforms such as saw-tooth waves
or
square waves.
• ,
~~
F
(V
,~1,t~~e
1
f ontrolle~ Filter) r
,,
1
This circuit alters the timbre by accentuating) oc ·filtering ·
ou
t certain l
i'
armonics ·
of
-
th
e
li
waveforms cre
ated
by
the VCO. The VCF might be called the most
important
part
of
an analog synthesizer.
-6
7-
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