:
ltre
sulcjective effect of reflections
(detayed
replicas
of an original
sound)
depends on the lengttr
of the
delay as follows:
-
Single
or
nultiple
delays up to about 40 milliseconds
after
the
direct sound alters ttre atr4nrent
character
of
quality,
but are
not
perceived
separately.
Ilpically, they add ttre sort
of
nfullnessn
and
body
wttich
a
voice
has in a
living
room,
but
lacks when
heard outdoors.
lhey are calIed
"earlyn
reflections.
-
A single delay
within
about 40 milliseconds
and having
the sane
volune
Ieve1 as the direct sound,
produces
an effect
souettring
like
that
heard l*ren a
solo
voice is replaced
by two identical voices
singing in
unison. Ttris
is
cal1ed
"dorrbIing".
-
A single delay
longer ttran 40 to 50 milliseconds
starts to
break
away from the original sound and be
perceived
as an echo.
-
A
longer
deIay,
i.e.7 over 100 mS and
sr:bstantially lower in 1evel
ttran
ttre original sound,
is heard
as a
nslatrback"
echo like
ttrat from
ttre
rear
waIl
of
a
cathedral
or other large
space. Of
course, to be
acoustically auttrentic, any
delay
must
be
lo*er in leve1
ttran
the direct
sound. A delay
rtrich
is sulcstantially louder
than the
dry sound
Wilt
be
perceived
as the original, and the original
sound
will
a54nar
to
be
a false
pre-echo.
-
ReSnated delays
at intervals
greater
than 50 milliseconds
are
trnrceived
sinply
as
multiple echos.
If ttre
trnttern
of
nultiple de1a1c
becones more complex
with
dozens or
hundreds
of echos
per
second
in
a
Snttern
which
fades
progressively
away
into
inaudibility,
ttren ttre
echos
are
trnrceived
as a single
continuous
sound
-
reverberation.
Acoustically
auttrentic reverberation
includes
sore
nearly"
reflections
beyond
100 ffi
becoming
progressively
closer in strncing
as ttrey fade away. If
ttre
reflections are
slnced
at unfiform intervals in
tfure
(e,9.,
a sinple
string
of echos 40
nS
agnrt),
the reverberation
of
transient sounds acquires a
chattering
gality
known as
'flutter
echor, or
"hard
reverb'.
a. DIS(REIE
rcI0S, STAPBACK
Feed
a signal
into
ttre EFFFIBOI{ IIrs inSutr
Sush
ttre echo
button
and
ttren
increase ttre
DEIAY FACIOR until ttre delay tine is
long
enough
to be
trnrceived
as
a discrete echo. While
ttris echo
can be
mixed directly
with
the
dry sound,
a more interesting
result is
usually
obtained by
panning
ttre echo elsewhere in
the stereo image
with a stereo
mixer; i.e.7
place
ttre dry sound on ttre
left
and
the
echo otr4nsite it on the right.
Itre
echo usually
should be a
bit
lower in leve1 than the
dry source.
Itris
left-right echo bouncing effect is
lnrticularly
useful wittr
a
regular drum
beat or a tr,ro-note
guitar
figure that is
used to set
the
beat.
B1r varying
the DELAY
FAC:IIOR,
lotl
IIBy be able to
slznchronize
ttre
echo
interval to match the
rhythm
of
ttre
rmsic
so
that ttre source
and its echo faIl on alternate beats.
10
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