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The prevalent technique for placing the image of a
source within a stereo sound field is to pan the signal
from left to right, relying on the amplitude difference
between
the channels
to create the perceived image
position.
But certain
advantages
can
be realized
by
using delay in conjunction
with, or even
in place of,
conventional panning. Imaging by means of level differ-
ences alone works well only for listeners located mid-
way
between
the two loudspeakers;
at off-axis loca-
tions, the image shifts toward
the loudspeaker
from
which
the
sound
arrives
first,
a
psychoacoustic
phenomenon
known as the Haas effect.
The Haas effect arises from the brain's ability to iden-
tify similarities between
sounds arriving at the ears at
different times.
Any sound
sufficiently similar to one
which
arrived at the ears within the previous 30 milli-
seconds will be perceived as a reflection of the original,
and the brain will localize the source as coming from the
direction of the first arrival. The greater the delay be-
tween the two arrivals, the more the source's apparent
location shifts toward the first one.
The Haas effect can be transformed from a problem
into an asset by using it in a controlled way to shift the
apparent position of a sound source in the stereo field.
With the PCM 42 connected in the Basic Stereo Setup
as shown in Fig. 4.3, simply adjust the delay to achieve
the
desired
degree
of apparent
offset
of the sound
source.
Delaying the sound
in the right channel
will
cause
the source
to shift to the left, and vice versa.
Delay times of 5-30 ms are most useful; above 30 ms,
the delayed sound begins to be perceived as a separate
echo, destroying the effect. (For additional information
4.2.1 Layering and the Infinite Repeat Mode
DELAY XZ
LEWER
FEEOGACK
FUER
SET MODE
OL
me
CLK
ot
=
OF cox
O
rgd
"y
%
on this subject, consult Lexicon Application Notes AN-2
and AN-3.)}
4.2 SPECIAL APPLICATIONS
OF LONG
DELAY
4.2.0 Introduction
The
class
of musical
applications
for long
delay
{greater than one second) is somewhat distinct from the
applications discussed above. These are closely akin to
results obtained with tape loops, but the special quali-
ties of digital delay and the unique features of the PCM
42 allow much greater freedom than is attainable with
tape, even without the PCM
42's obvious advantages
over
a couple
of high-quality
open-reel
recorders
in
compactness,
ruggedness and cost.
Many
techniques
previously confined to home or studio can now be used
in live performance.
In general terms, the use of very long delays in music
produces a type of 'canon'
or polyphonic
effect by
superimposing the audio image of previously performed
phrases over current material. With no feedback, only
one previous phrase will be audible, but if feedback is
added,
each delay period will repeat more
than once
before it dies away. With large amounts of feedback,
the performance will pile up, one phrase over another,
until input to the delay line ceases or the unit is placed
into the infinite repeat mode. At full feedback and max-
imum delay time (with the optional memory extension)
the decay time of the PCM 42 exceeds 3 minutes!
PARAL
GEPTH
WAVEFORM
RY
DELAY
Figure 4.5-| — CANON
This option begins to make use of the multilayering potential of the PCM 42. The delay time should be set at the max-
imum available; for machines with the memory option, the MANUAL
VCO-SWEEP
control will be at about 10:30
o'clock.
Using this overlay technique, it is possible to create
compositions and rhythmic beds in real time that can be
trapped via infinite repeat, or continuously evolved by
adding new notes as older ones are tading out. When
the repeat function is used, the resulting backgrounds
may be soloed over without entering the notes into the
delay loop.
19
itis important to be aware of the nature of the Infinite
Repeat function in the PCM
42 in order to make full
usage of the looping technique. WHEN
THE INFINITE
REPEAT MODE iS ACTIVATED, THE FULL MEMORY
IS ALWAYS UTILIZED. The length of the segment cap-
tured
in memory
is independent
of the
delay
tap
selected by the UP and DOWN
pushbuttons.
It is af-
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