Frequency Modulation; Fm Algorithms - Clavia NordStage2 EX 88 User Manual

When using Oscillator Sync, it can be very useful to have the
Shape amount(s) modulated from any of the Morph assign
sources, or by the Modulation Envelope. This will generate a signal
with continuously varied harmonic content.

Frequency Modulation

The basic principle behind frequency modulation (FM) synthesis is to
have one oscillator (the modulator) modulating the frequency of another
(the carrier). The carrier can in turn modulate the frequency of yet
another oscillator, etc. There are several different algorithms in the FM
category ranging from one up to three oscillators (operators) modulat-
ing each other in series, with or without feedback on the first operator
in the chain.
The image above shows a 2 Operator FM-Synthesis setup, and the
resulting waveform using a fairly high FM amount setting.
The resulting waveform is far more rich in harmonics than the original
Sine waveform, and drastic changes in tonal character are provided by
altering the amount of modulation.
Modulator
There are several FM algorithms available; set-ups with various number
of oscillators, feedback and frequency ratio settings between the oscil-
Shape1
lators.
(FM Amount)
• Use the Waveform-dial to select the FM-algorithm.
• The Shape parameter is used for setting the amount of modulation
and/or feedback from none to maximum.
Carrier
There are three main FM algorithms in the Nord Stage 2 EX: one, two OSC MOD
and three oscillator FM with feedback. The feedback is not active in all
algorithms.
The Shape knob controls the FM and feedback amounts. When you
turn the knob, all modulations are increased simultaneously. The
number of harmonics, and their intensity, increase proportionally to the
FM amount. As usual, the Shape parameter can be modulated by the
Modulation Envelope or the LFO, and it can be Morph controlled by
any combination of wheel, aftertouch and pedal.
Modulator
Shape2
(FM Amount)
Carrier
OSC MIX
Shape
(Feedback)
Each algorithm comes with a number of pre-configured frequency
ratios. Depending on what kind of sound you want, choose from the
different combinations available and you have many interesting FM
sounds at your disposal. When a new algorithm is selected, the Main
display shows, for a short duration, the algorithm together with infor-
mation on the frequency relations between the operators and whether
feedback is used. The display shows the modulator(s) frequency
relation to the carrier. If an operator uses feedback, it is indicated by a
dot next to the digit. In the chart below all available algorithms together
with the notation used in the display are listed:

FM Algorithms

LED LCD Description (FB = feedback)
Sin 1-OP (+FB) Carrier only, with feedback
1 1 2-OP 1:1
Carrier + Modulator, same frequency
2 1 2-OP 2:1
Carrier + Modulator, frequency ratio 2:1
3 1 2-OP 3:1 Carrier + Modulator, frequency ratio 3:1
4 1 2-OP 4:1 Carrier + Modulator, frequency ratio 4:1
5 1 2-OP 5:1 Carrier + Modulator, frequency ratio 5:1
6 1 2-OP 6:1
Carrier + Modulator, frequency ratio 6:1
7 1 2-OP 7:1
Carrier + Modulator, frequency ratio 7:1
8 1 2-OP 8:1 Carrier + Modulator, frequency ratio 8:1
91 2-OP 9:1 Carrier + Modulator, frequency ratio 9:1
1.1 2-OP 1:1 (+FB) Carrier + Mod + FB, same frequency
2.1 2-OP 2:1 (+FB)
Carrier + Mod + FB, frequency ratio 2:1
3.1 2-OP 3:1 (+FB)
Carrier + Mod + FB, frequency ratio 3:1
4.1 2-OP 4:1 (+FB) Carrier + Mod + FB, frequency ratio 4:1
5.1 2-OP 5:1 (+FB) Carrier + Modulator, frequency ratio 5:1
6.1 2-OP 6:1 (+FB) Carrier + Mod + FB, frequency ratio 6:1
7.1 2-OP 7:1 (+FB)
Carrier + Mod + FB, frequency ratio 7:1
8.1 2-OP 8:1 (+FB)
Carrier + Mod + FB, frequency ratio 8:1
9.1 2-OP 9:1 (+FB) Carrier + Mod + FB, frequency ratio 9:1
9.1 2-OP 9:1 (+FB) Carrier + Mod + FB, frequency ratio 9:1
111 3-OP 1:1:1 Carrier + Mod + FB, same frequencies
211 3-OP 2:1:1
Carrier + Modulators, frequency ratios 2:1:1
311 3-OP 3:1:1
Carrier + Modulators, frequency ratios 3:1:1
511 3-OP 5:1:1 Carrier + Modulators, frequency ratios 5:1:1
911 3-OP 9:1:1 Carrier + Modulators, frequency ratios 9:1:1
221 3-OP 2:2:1
Carrier + Modulators, frequency ratios 2:2:1
421 3-OP 4:2:1
Carrier + Modulators, frequency ratios 4:2:1
821 3-OP 8:2:1
Carrier + Modulators, frequency ratios 8:2:1
1.11 3-OP 1:1:1(+FB) Carrier + Mod + FB, same frequencies
1.21 3-OP 1:2:1(+FB) Carrier + Mod + FB, freq. ratios 1:2:1
1.31 3-OP 1:3:1(+FB)
Carrier + Mod + FB, freq. ratios 1:3:1
1.51 3-OP 1:5:1(+FB)
Carrier + Mod + FB, freq. ratios 1:5:1
1.91 3-OP 1:9:1(+FB) Carrier + Mod + FB, freq. ratios 1:9:1
1.F2 3-OP 1:1:2(+FB) Carrier + Mod + FB, freq. ratios 1:1:2
2.F2 3-OP 2:1:1(+FB) Carrier + Mod + FB, freq. ratios 2:1:2
3.F2 3-OP 3:1:2(+FB)
Carrier + Mod + FB, freq. ratios 3:1:2
5.F2 3-OP 5:1:2(+FB)
Carrier + Mod + FB, freq. ratios 5:1:2
9.F2 3-OP 9:1:2(+FB) Carrier + Mod + FB, freq. ratios 9:1:2
Tip! The one-operator algorithm can be used to produce a perfect
sine-wave, if the Shape knob is set to zero.
Chapter 8 Synth | 31