In a
concert
environnrent, the
listener hears
the direct sound
from
ttre
perfonner,
folloued
by
trearlyn
reflections from the floor
and
wa1ls
of the stage
and finally the reverberation
ourprised
of long
delap
as sound
is
reflected anong ttre
walls
of ttre
auditoriurn.
When
using
a reverb slctem to
process
dry studio sound,
pre-reverb
delay
can
also serve as ttre
'early'
stage-area reflections, sinply
by including thern
in ttre mix.
d.
IIAAS-EFFFT IMA@
SHIFTIIiG
ftre
ear
has an integration tire
of about 40 mS.
ff
a
sound
is
heard from one direction
and the sane sound also arrives at
a
later tine
from another direction, the second
arrival
will
not be
heard
at all if the
interval
betr,ueen
the two arrivals
is less
ttran
40
mS.
Ihe
later arriving sound
may even
be
several dB
higher
in
level than
its
earlier
counte4nrt; neverttreless, the
ear will
hear
both
sounds
as a single
louder
sound
located in the
direction
of the first
arrival. ftris
is ttre
precedence
effect
-
or
ltraas
effect
-
and
it
can be used
to stabilize
innges in
a stereo sourd
f
ieId.
For
exarple,
if a signal
is
recorded
in
both channels,at
identical
1eve1s,
the
feed to the right channel
is
delayed,
tkren the
sound
will
be
trnrceived
as
originating
exclusively
in
the
left
channel.
In
principle,
the
delay
to ttre otr4nsite channel
nray be
anything
from
l rnS
to
40
mS. But, long
delays carry
the risk ttrat
sore
listeners my begin to
Snrceive
ttre delayed sounds
as an
echo; and
if
ttre delay
is
under
10-15 mS
coloration
due to corb
filtering could
becore a
problem
if ttre two channels are
later
mixed
together
(for
AtlI broadcast,
for
instance).
A delay
of around
20 mS
usually
turns
out
to be
optimum for
Haas-effect
image
panning.
It
is
trnssible
to keep
the signal
level
constant
in
both channels
and cause
the innge to
jump
back
and forth from
left
to right by
swalping
the delayed
and undelayed signals by
panning
the rnixer.
2.
FEDBACK
CIE
StrOR[ DEI,ASS
By using the
feedback control, the delayed
signal
is fed
back
and mixed
with
the
incoming audio signal
and thren the congnsite signal
is encoded and read
into
the digital
delay circuits.
Itre strength
and tonal
Erality
of ttre
feedback rnay be
adjusted by
the
user.
Ihe maxinnrm
feedback
gain
is
less
than unityi tttus,
like a real sound
reflecting off any surface,
the recycled
signal
is
at
least a
little weaker than ttre original,
drld as ttre sound
is
retrntitively
recycled through
ttre system,
it
gradually
fades away.
d. CClvlB FILtERIIG
Whenever
any original sound
and
a
delayed
version
of
itself are
mixed together,
the
two sounds
are mutually
reinforced at sone
frequencies
and
tend to nnrtually
cancel
at
other
frequencies.
Itris
rccurs
in an electronic delay
line and
it also is a comrpn
acoustic
tr*renorenon
both
in recording
(v.ltrere
the
mike
picks
up
12
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