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Algorithms
Different arrangements of operators are known as
"algorithms." An algorithm is something like a "patch"
on a modular synthesizer; it defines the way the opera-
tors are interconnected, only instead of using patch
cords, the DX synthesizers digitally switch the operators
to make up the various algorithms. The DX7 lets you
select among 32 different algorithms. Referring to the
diagrams on the top panel of the synthesizer, the small
boxes numbered 1-6 are the operators, and each "map"
pf operators (numbered 1-32) is an algorithm:
ALGORITHM
#
1
Algorithm 1 has 2 carriers and 4 modulators
stack of
3 modulators
& 1 carrier
A given arrangement of OPERATORS is called an AL-
GORITHM. The available Algorithms are numbered.
Illustrated here is Algorithm
#
1, which happens to have
2 parallel STACKS, one with 2 operators, and the other
with 4 operators.
The relationship between algorithms and the
sound
By changing the relative frequencies of each operator,
you can change not only the fundamental pitch of the
note, but also the frequencies present in the note's har-
monic structure. Thus, the timbre of the voice can be
precisely controlled. In addition, because each operator
has its own envelope, the harmonic structure of a note
can be programmed to change over time, just as a
plucked string changes its overtones as the note decays.
Depending on the selected algorithm, operators can
be stacked up vertically ("series connected"), arranged
side by side ("parallel connected") or both. In the vertical
arrangement, when the output of one operator is con-
nected to the input of the next, the result is modulation
— the essence of FM synthesis. By convention, we call
the operator at the bottom of a vertical stack the "car-
rier", and any operators that are above and which feed
its input are known as "modulators." By increasing the
output level of the modulators) going into a given the
carrier, you increase the number of harmonics present,
extending the bandwidth of the voice (making it more
"brilliant").
The bottom operator of a
stack is called a CARRIER.
Any operators which are
connected to the carrier's
inputs are called MODULA-
TORS. YOU CANT HEAR A
MODULATOR DIRECTLY,
but you hear its effect by
listening to the carrier's
altered (modulated) output.
A given operator can be
either a carrier or a modu-
lator: the only difference is
how it is "connected" in a
given algorithm.
Most algorithms have multiple carriers and modula-
tors. In one algorithm a given operator may be a carrier,
while in the next algorithm it may be a modulator —
the only difference is how it is connected. In algorithm
#
5, for example, there are 3 vertical stacks connected in
parallel, and each stack has a single modulator con-
nected to a single carrier. Thus algorithm 5 has an equal
number of carriers and modulators (3 of each). In con-
trast, all 6 operators in algorithm
#
32 are carriers... there
are no modulators, while in algorithm
#
16 there are 5
modulators and just 1 carrier.
As you move from algorithm
#
32 to
#
1, there is a
greater potential for increased harmonic complexity due
to the structure of the algorithm. However, the algorithm
alone does not determine the sound. The actual nature
of the sound you achieve is highly dependent upon the
frequencies and levels you program into the operators
(modulators and carriers). The 32 algorithms available in
the DX7 were selected because they offer a broad spec-
trum of useful programming possibilities.
ALGORITHM
#
5
Algorithm
#
5
has 3 carriers and 3 modulators
ALGORITHM
#
I6
Algorithm
#
16 has 1 carrier and 5 modulators.
ALGORITHM
#
32
Algorithm
#
32 has 6 carriers and no modulators.
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