B.6 HARMONICS

APPENDIX B: THE FM TONE SYNTHESIS > B.6 HARMONICS · PDF p. 109–111 · OS 1.10D

# B.6 HARMONICS

APPENDIX B: THE FM TONE SYNTHESIS
Reset on (ARST/BRST ON)
Trig
Trig
Reset off (ARST/BRST OFF)
Trig
Trig
The LEVEL parameters on the SYN2 page controls the amount of modulation from the A and B operators.
For more information, please see “A.2.1 FM TONE” on page 89. The LEVEL parameter for B is macro
mapped to both operator B1 and B2 and control their modulation amount as per this graph:
B1
B2
Level
Parameter value
B.6 HARMONICS
The default output from an operator is a sine wave, but you can use the HARM parameter to add upper
partials to some of the operators’ sine waves to create more harmonically rich waveforms. The HARM pa
rameter is bipolar. Negative parameter values change the harmonics of operator C, while positive parameter
values change the harmonics of operators A and B1.
Harm -
Harm +
When changing harmonics, intermediate values interpolates between the current and the next harmonic.
This interpolation works much like in wavetable synthesis, sweeping between the harmonics, smoothly
transitioning from one timbre to another. For more information, please see “A.2.1 FM TONE” on page 89.
The harmonic series for the operators looks like this:

APPENDIX B: THE FM TONE SYNTHESIS
Saw
(All partials)
Saw reduction
Odd/Even Mix
Square
(Odd partials)
Square
reduction
Bell
The Digitone II uses a form of additive synthesis to create the harmonic series for the HARM parameter.
Additive synthesis is one of the oldest forms of electronic sound generation. It is a quite simple form of
synthesis but still very powerful. The basic principle is to add multiple sine waves together to form complex
timbres. Each sine wave is called a partial. By attenuating each partial, the timbre changes its harmonic
content, resulting in different waveforms.
The first partial is always kept
at full volume, which keeps the
base octave intact.
Adding every partial in series
will replicate a sawtooth. Note
how the volume decreases for
each partial, creating a natural
falloff.
Adding every odd partial in
series will approximate a
square wave.
The additive method can be
used to make many different
timbres. This combination of
partials, for example, sounds
close to a bell tone.

APPENDIX B: THE FM TONE SYNTHESIS
B.7 SYN PAGE 1 PARAMETERS OVERVIEW
Here is a graphical overview of what part of the FM engine the parameters on the SYN1 pages affects. The
affected part of the FM engine is highlighted with grey. For more information, please see “A.2.1 FM TONE”
on page 89.
Detune
Ratio A
Ratio B
Ratio C
Harm -
Harm +
Feedback
Mix

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